Laundered Shop Towels 8: A child's hand is not an adult's hand

That title is one of those "duh!" types of statements.

So if that's true, why did Gradient base the hand to mouth efficiency (HTE) on studies involving 1-6 year olds?

Not that there is anything wrong with that, but in this case, we are dealing with adult workers and assumptions should have been made using adult data - that was readily available to them.

Gradient states in their 2003 study the following:

Gradient used the median skin surface area data specific to a 1- to 6-year-old child and applied the soil AF derived from Roels to estimate the average mass of soil on the hands for a 1- to 6-year-old child, which is approximately 145 mg for both hands.

A median soil ingestion rate of 38 mg/day for children ages 1 to 6 years was calculated based on a soil ingestion study conducted in Amherst, Massachusetts.

This soil ingestion rate was divided by the hand soil-loading estimate for a child resident (approximately 145 mg on both hands), for a daily HTE value of approximately 0.26 hand loads per day.

In this report, we used half of 0.26 as the HTE value for adults, or 0.13. 

Using a smaller HTE for adults as compared to children is further supported by the United States Environmental Protection Agency's (USEPA) soil ingestion rates:  their recommended mean soil ingestion rate for adults is exactly one-half of the value for children less than 6 years of age (USEPA, 1997a)

That HTE value of 13% was based on dividing the amount of soil a child consumes in a day by the amount of soil both hands of a child can hold (soil-loading).  Read my previous post on this for more information.

That amount, 26%, was then divided in half to represent the HTE for an adult, 13%.

Sounds good until you think about it a little more closely.  See it?  Yeah, you can fly a Russian Antonov An-225 through this one.

According to Gradient, the "145 mg for both hands" was calculated as follows:

Gradient then divided the average amount of soil adhering to the hands by the “available” skin surface of the hands for the average age of the children included in the Roels study (i.e., 11-yearolds) to generate a soil adherence factor (AF) of 1.1 mg/cm2 for both boys and girls.  

The skin surface area of the hands available for contact with soil is assumed to be approximately one-third of the total surface area of both hands.

If that assumption holds true, why didn't Gradient use "one-third of the total surface area of both hands" for an adult?

To get the HTE of 13% the "median soil ingestion rate of 38 mg/day for children ages 1 to 6 years" was divided by "145 mg for both hands."

If we assume (according to the EPA) that the "mean soil ingestion rate for adults is exactly one-half of the value for children less than 6 years of age," wouldn't it have been more appropriate to take one-half of 38 mg/day - 19 mg/day - and divide that by  "one-third of the total surface area of both hands" for an adult?

If that assumptions for a child holds true, this would have been a more appropriate - or scientifically sound - method to calculate the HTE for an adult worker.

You can ask Gradient why they did not use this method to calculate their HTE.  Even more peculiar is why they did not use an established calculation to estimate hand to mouth intake for an adult.  A little bit of Google searching brings up this document from the CalEPA:

Guideline for Hand-to-Mouth Transfer of Lead through Exposure to Consumer Products

Here is what CalEPA says on page 12:

The U.S. EPA Exposure Handbook provides representative hand surface area values for both adults and children in Chapter 6, General Factors for Dermal Route.  Detailed data distributions of hand surface area (mean, standard deviation and percentile distributions) by gender and age are provided in Tables 6-2 to 6-8 (U.S. EPA, 1997). 

Gosh...I wonder what that source is?

U.S. Environmental Protection Agency (U.S. EPA, 1997). Exposure Factors Handbook.  National Center for Environmental Assessment, Office of Research and Development, Washington, DC, EPA/600/p-95/002F a-c.

That sounds familiar...I wonder where I saw that source mentioned before?  Oh, yeah, it was referenced in the 2003 Gradient study on laundered shop towels:

Source: 2003 Gradient Study

Why's that important?  Well in that EPA handbook is data that Gradient should have used.  Here is what CalEPA goes on to say:

From the U.S. EPA Exposure Handbook, the representative value of the surface area of both hands in adults is 750 cm2 for women and 840 cm2 for men. 

I wonder what the HTE would be if we used the values assigned to adults?  Let's see:

"The skin surface area of the hands available for contact with soil is assumed to be approximately one-third of the total surface area of both hands."  So if we multiply 840 by 0.33 we get 274 cm2

"Gradient then divided the average amount of soil adhering to the hands by the “available” skin surface of the hands...to generate a soil adherence factor (AF) of 1.1 mg/cm2 for both boys and girls."  So if we multiply 274 by 1.1 we get 301 mg on both hands, this is the "soil loading" estimate.

If the adult "mean soil ingestion rate for adults is exactly one-half of the value for children less than 6 years of age," we would take 38 mg/day and divided it by 2, which would give us 19 mg/day. 

 "This soil ingestion rate was divided by the hand soil-loading estimate...for a daily HTE value..." So, if we divide 19 by 301 we would get an adult male HTE of  6%.

As I pointed out in a previous post, this method of calculating an HTE is flawed because it assumes all the soil ingested in a day comes solely from the hands.

Still, though, if Gradient was going to calculate an HTE based on this method, it would have made more sense to use adult values, which would have been calculated as 6%.

Does an HTE of 6% instead of 13% affect their findings?

Recalculation - Table 8 of 2011 Study

I had to tweak the "Average Load" values in Table 8 upwards to get the same intake values they calculated.  The values in blue represent the intakes one would see if a 6% HTE was used.  At a 6% HTE, the Exceedance Ratios in Table 8A are changed as follows:

You can see that there are still exceedances, but adjusting just one variable, the HTE, changes the results considerably.  Now, consider the other parameters "assumed" to be correct by Gradient.  Every value that is used that is higher than would actually be in reality (mean. maximum, towel transfer efficiency, number of rags used), exaggerates the "exceedance ratios" Gradient reports.

Yeah...but look at lead!  It's still 273 times higher than CalEPA's MADL.... and five times higher for cancer.  Explain that!

Those exceedance values are only applicable if you accept Gradient's HTE..  Remember, Gradient calculated that percentage based on ALL of the soil consumed in a day coming from the hands.  13% or 6% is based on that premise, which is not the sole mechanism for soil intake into the child or adult. (see post).

A better way to calculate how much lead (metal) would be transferred from the hand to the mouth would have been to use a more plausible calculation....like the one that CalEPA has developed.

Next Post: Laundered Shop Towels 9: CalEPA's Lead Intake from Direct Hand-to-Mouth Contact


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Laundered Shop Towels: 7 - Fun with graph paper.

I got to thinking about what is involved in Gradient's model and equation.  That is, if there is intake of lead each and every time a laundered shop towel is handled, how would this transfer from hand to mouth take place in a work environment.

According to the model:

Source

And the equation:

Source

The lead (metal) is transferred to the hand through a "towel to hand transfer efficiency" or "Tt/h" which I discussed in a previous post.  The Tt/h is a unitless number in Gradient's equation, and is a percent (0.13) of what is on calculated to be on the towel (Loadtowel) surface (mean/maximum).

What Gradient's equation states is this.  If the towel contains X amount of lead per square centimeter, the towel will dislodge 13% of X that is on each centimeter of towel.  They then go on to calculate that the hand will only come in contact with 75% (Ftowel)  of the towel's surface area (SAtowel).

On the hand will be 13% of X from 75% of the towel.

Gradient assumes that the towel has the lead (metal) evenly dispersed on each of the 2,268 square centimeters that make up a laundered shop towel's surface area.  The "load" is found on Table 2 of the report.  For lead, it is as follows:

• Average = 0.0012  mg/cm2
• Maximum = 0.0075  mg/cm2

If we are looking at the average concentration of lead found (mean) each square centimeter of the towel's surface is considered to contain 0.0012 mg/kg of lead.

The hand, coming in contact with 75% of the laundered shop towel's surface area, is assumed to dislodge 13% of the lead onto the hand. (let's ignore N for the time being)

• 0.0012 x 2268 x 0.75 x 0.13 = 0.26 mg

Gradient assumes that each towel with an average concentration of 100 mg/kg of lead will place onto the hand 0.26 mg of lead.

This is where it get's a bit...complicated.

Gradient assumes that the hand with the 0.26 mg of lead will come in contact with mouth, and when it does, 13% of that amount will end up in the mouth (intake).

They base that 13% hand to mouth transfer efficiency (HTE) on the how much soil is consumed in a day by a child divided by how much soil is contained on a 1-6 year old's hand.  They then cut that percentage in half because " The smaller HTE value used for adults reflects the reduced hand-to-mouth behavior in people greater than 6 years of age."  You can read more about this in my last post.

But back to where I was going with this.

If the HTE is 13% like Gradient assumes it is, how would 13% of 0.26 mg be transferred from the hand to the mouth?

Rule number 5: Always make sure the model and equations reflect reality.

Regardless of what studies one looks at, the model and calculation you develop must reflect the actual reality for the situation you are describing.

If we are to assume that an employee places his hands to his mouth each and every time they use a laundered shop towel, then we must assume there is a plausible mechanism for this to take place.

If the shop towel transfers and evenly spread out load of lead onto the hand, how much of the hand needs to come in contact with the mouth to transfer 13%?

Gradient assumes that the transfer efficiency is 13%.  That is, if the whole hand was placed into the mouth, only 13% of the lead would come off the hand.

Think about that for a minute.

Gradient is basing the intake on the efficiency of transfer.  That is, each square centimeter of hand surface area that came in contact with the towel can only transfer 13% of that load into the mouth.

This requires one of two things.

1. The whole contact surface area of the hand is placed into or up to the mouth
2. The 75% surface area of the laundered shop towel only comes in contact with the the part of the hand that comes in contact with the mouth.

Do any of those two situations seem plausible?

Because the assumption for the HTE is flawed, the amount of metals, such as lead, Gradient calculates getting into the body is flawed as well.

And this is why my question of "how" is important.

To have 13% lead transfer from the hand to the mouth, either the whole hand is placed into the mouth or licked, or 13% of the surface area of the hand is contacted with the mouth for 100% transfer efficiency (which is not what their equation is based on).

Let's assume that we have 100% transfer efficiency (which is not supported by any of the studies they looked at).  How much surface area of the hand would need to come in contact with the mouth?

Once again, we need to look at Gradient's model and equation.  Gradient assumes that only one hand is used in their equation, which means that the total amount of lead, 0.26 mg, will reside on one hand and it will be that hand that contacts the mouth.  It also appears that they assume only the front of the hand (palm and inside fingers/thumb) come in contact with the towel.

So here is what I did, when I got to thinking about this.

How much surface area of an employees hand would come in contact with the laundered shop towel?

This required a one centimeter by one centimeter sheet of graph paper, and a pen.

I roughly calculated the surface area of my hand by taking the total surface area of the box (345 square centimeters) and subtracting the number of boxes outside of the outline (157).  Based on my calculations (and you can see why I am not an engineer), the surface area of my hand that could come in contact with a laundered shop towel is 188 square centimeters.

I'm stepping out on a limb here, but assuming I have a two dimensional flat surface hand, how much of that surface area represents 13%?

For the finger tips, it looks like this:

Red blocks = 13% of total hand surface area

For the palm, it looks like this:

Red blocks = 13% of total hand surface area

It is reasonable, I think, to assume that if the hand contacts the mouth it would do so either at the fingertips or the palm.  The question then comes down to this:

1. Is it reasonable to assume that much of the fingertips or palm will contact the mouth each and every time an employee picks up a laundered shop towel?
2. Is it reasonable to assume that 100% of the metal in that area will be removed from the hand and put into the mouth?

In the two graphics above, each red square assumes a transfer efficiency (HTE) of 100%.  In gradients equation, the hand to mouth transfer efficiency (HTE) is 13%.  In order to get to get 13% of 0.26 mg of the lead now on the hand into the mouth, how much surface area of the hand needs to contact the mouth?

Gradient assumes that 75% of each square centimeter of the laundered shop towel transferred onto the hand 13% of the load.

If the "average" load for lead is 0.0012 mg/cm2, then  0.26 mg total of lead must be transferred onto the front of the hand.  If we assume a 13% HTE (as Gradient does) how much surface area of the hand would need to contact the mouth to give an intake of  0.34 mg of lead (0.26 x 0.13)?

In order for Gradient's equation to work, the metal must be evenly distributed all over the face of the hand.  If you assume that it is on the fingertips only, then the assumption is the fingertips are the only part of the hand that contacts the mouth.  Same goes for the palm.

But that's not what their equation assumes.  It assumes a transfer efficiency of 13% each and ever time the laundered shop towel is used.

How is this done?  Gradient assumes that the entire surface area of the hand contacts the mouth.

In order to get 0.34 mg of lead into the body, a hand with the surface area of 188 square centimeters must have 0.014 mg of lead on each square centimeter (0.26/188), assuming a HTE of 13%.

To limit the part of the hand to the mouth, condenses the amount of contaminant per square centimeter and also assume that only that part of the hand will contact the mouth.

For a hand with a surface area of 188 square centimeters that will contact 75% of the laundered shop towel, Gradient's calculation assumes that this much of the hand will have contact with the mouth.

That's right, each and every one centimeter square box inside the outline of my hand will need to contact the mouth each and every time a laundered shop towel is used.

Do the math:

• 0.0012 x 2268 x 0.75 x 0.13 x 0.13  = 0.034 mg of lead into the mouth.

Question: How much of the hand must come in contact with the mouth if there is a 13% HTE that takes place each and every time a laundered shop towel is used?

Answer: The whole surface of the hand.

Does that look anything like their graphic is showing?

Does their equation represent reality for a worker using a laundered shop towel?

Still not convinced that their report is flawed and that laundered shop towels do not pose an increase in risk even remotely close to their calculations??

Read on.

Next post: Laundered Shop Towels 8: A child's hand is not an adult's hand.

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Laundered Shop Towels: 6 - Finger Lickin' Good!

The basis for Gradient's model is that each laundered shop towel will transfer 13% of the load from 75% of the towels surface area onto the hand.  The hand will then be placed to the mouth and 13% of what is on the hand will be transferred into the mouth.  That second "13%" transfer is what Gradient calls a hand to mouth efficiency - "HTE" - value:

The HTE transfer is based on estimates of the amount of soil transferred by children from the surface of their hands to the mouth, where it is subsequently ingested, but is adapted for adults, based on a lower HTE value, to be consistent with the lower ingestion rate of adults. (Page 9)

Here is how Gradient came up with this value (excerpt from their 2003 study)

Daily Hand to Mouth Transfer Efficiency. To estimate the amount of metal on the hands that might be ingested via hand-to-mouth contact, we used a hand transfer efficiency, or HTE parameter, of 0.13. 

The HTE parameter quantifies the fraction of material on the hands that is likely to be transferred to the mouth and ultimately ingested. 

The HTE transfer is based on estimates of the amount of soil transferred by children from the surface of their hands to the mouth, where it is subsequently ingested.

Gradient used the median skin surface area data specific to a 1- to 6-year-old child and applied the soil AF derived from Roels et al. (1980) to estimate the average mass of soil on the hands for a 1- to 6-year-old child, which is approximately 145 mg for both hands. 

Gradient then combined the estimate of soil loading on the hand with an estimated soil ingestion rate to derive the hand transfer efficiency (HTE) value, which is an estimate of the fraction of the mass of soil adhering to the hands that would need to be ingested to yield the estimated daily soil ingestion rate. 

Read that last paragraph again.  I'll wait.  And while you are reading it, here is some music to set the mood.  With that premise, Gradient came to this:

A median soil ingestion rate of 38 mg/day for children ages 1 to 6 years was calculated based on a soil ingestion study conducted in Amherst, Massachusetts. 

This soil ingestion rate was divided by the hand soil-loading estimate for a child resident (for a child resident (approximately 145 mg on both hands), for a daily HTE value of approximately 0.26 hand loads per day.

If you are reading this and paying close attention you will see what they have done and why it should be viewed as inappropriate for this study.  If you want to read about the Amherst, Massachusetts, you can see a summary about it here.  Let's look at the first part of the abstract for the Calabrese & Stanek paper:

Sixty-four children aged 1-4 years were evaluated for the extent to which they ingest soil. [t]he present study included a number of modifications from the Binder et al. study. The principal new features were (1) increasing the tracer elements from three to eight; (2) using a mass-balance approach so that the contribution of food and medicine ingestion would be considered; 

See it? 

"contribution of food and medicine ingestion would be considered"

The "median soil ingestion rate of 38 mg/day" is based on the amount of soil consumed from ALL sources, not just from the hands.  Gradient has based the HTE on 38 mg/day of soil intake coming from the hands only.

For this to be true, the soil on the hands, 145 mg, would need to be placed on the hands - no more - no less - and no other soil consumed in the day.  To obtain an HTE of 0.26 all the soil intake had to come from the hands - both of them.

Gradient assumes that the child licks, touches, contacts the mouth with both hands so that 0.26 of the soil on both hands is transferred to the mouth.  The 38 mg/day is from all sources, including dust, mouth soil on surfaces, food, and contact with other sources throughout the day.

Gradient goes on to say:

In this report, we used half of 0.26 as the HTE value for adults, or 0.13. The smaller HTE value used for adults reflects the reduced hand-to-mouth behavior in people greater than 6 years of age. 

Using a smaller HTE for adults as compared to children is further supported by the USEPA soil ingestion rates: their recommended mean soil ingestion rate for adults is exactly one-half of the value for children less than 6 years of age.

I assume that the HTE is the same for one hand (their model) as for both hands.  Basically, as I understand it, Gradient assumes that 13% of what is on the hand will be transferred to the mouth.

You can see where they came up with that 13%.  It assumes that because 38 mg/day of soil is consumed for a child, and an adult consumes half that amount, it all had to come from the hand.

That's not true of course, soil consumption comes from many sources in a day, not just from the hands.  But I'll go with it for now...I'll assume that there is a transfer rate of 13% of the load on the hand into the mouth.

And once again I am perplexed to understand how that would happen.  What's the mechanics involved?

Kimberly-Clark tells us that "an average person touches their face 16 times per hour."  Does that mean a worker places one hand to his mouth each time he picks up a laundered shop towel?

And when the worker places his hand to his mouth, does he lick his fingers or rub his lips over the surface of the hand that contacted the towel?  And if this happens each and every time 12 towels are used per day, how much area of the hand would need to contact the mouth so that 13% of the load that is evenly distributed on the hand is transferred to the mouth?

For Gradient's model and equation to hold true, the hand must contact the mouth and 13% of what is on the hand must transfer to the mouth.  How?

Next post: Laundered Shop Towels: 7 - Fun with Graph Paper


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Laundered Shop Towels: 5 - That's quite a load

I've tried to make a case in my last four posts about why the concentration of contaminants used in Gradient's equation are most likely higher than what would be normally found in a laundered shop towel.

Additionally, because Gradient used the actual maximum concentration they detected instead of a statistical maximum "exceedance ratio," the maximum intake value is calculated higher than is statistically possible.  I've dealt with a lot of contaminated rags in my career, and I rarely see heavy metal levels that high in dirty rags!  Those concentrations identified by Gradient are for laundered shop towels - clean ones!

Without seeing the actual analytical reports (which I have requested from Gradient) I have to assume that the values identified in Table 2 of their 2011 Study are actually what was found.

Let's look at lead for example.  If lead has a mean concentration of 100 mg/kg and a maximum concentration of 600 mg/kg, then I will assume that those values are accurate.

Once again, we need to assume that these values accurately reflect what would indeed be found on a laundered shop towel.  If you can't accept this assumption as valid, then you cannot proceed to the next step in the model they are using.  Gradient has calculated an intake based on a model that proposes that the laundered shop towel transfers its heavy metals to the hand and the hand then transfers them to the mouth.

With that model and equation you can calculate the uptake which is what they call intake.

Gradient has developed an equation to calculate the intake expected for a worker handling these laundered shop towels.  That equation looks like this:

The first parameter, Load, is based on the following assumptions (see study Table 2 notes):

• The laundered shop towel contains either a mean or maximum amount of the heavy metal in mg/kg
• The laundered shop towel weighs 0.0283 kg
• The laundered shop towel has a surface area of 2,268 square centimeters (cm2)  

The Load - in mg/cm2 - is derived from the following:

[mean or maximum concentration x 0.0283] / 2,268

For example, the average (mean) Load for lead is:

[100 mg/kg x 0.0283 kg] / 2,268 cm2 =  0.0012 mg/cm2

What that lead Load value represents is the following:

The contaminant is evenly distributed on the laundered shop rag so that each square centimeter (cm2) of cloth contains 0.0012 mg of lead.

This is important because the hand to mouth transfer is based on how much of the cloth will contact the hand (Ftowel) and how much of the contaminant will be transferred from the cloth to the hand (Tt/h).

There is another assumption here that is implicit.  That is, the contaminant is not spread evenly on each side of the cloth, but instead is assumed to be on whatever side that will come in contact with the hand.  There is nothing wrong with that assumption, but for that to be true, other assumptions will need to be true as well.

How much - and where - the contaminant is on the towel does not matter at this point.  What matters is the assumption that it is evenly distributed so that the three other parameters...

1. Ftowel = Fraction of towel in contact with hand (unitless);
2. Tt/h = Towel to hand transfer (unitless);  
3. HTE = Daily hand-to-mouth transfer efficiency (day-1)

...will work to derive an amount of metal entering into the worker's mouth.

You can read Gradient's Study to see why certain values were used by the authors. For example:

• Gradient "assumed," based on professional judgment, that the hand (single) would contact approximately 75% of the total surface area of a laundered shop towel, under typical laundered shop towel usage.

What Gradient basis their intake values on involves a worker coming into contact with 75% of the Load (Ftowel).  For the heavy metal lead, it would be calculated as follows::

• 0.0012 mg/cm2 x 2268 cm2 x 0.75 = 2.72 mg = Ftowel

What that Ftowel value represents is the amount of lead the worker is exposed to when his/her hand comes into contact with the laundered shop towel.  Exposure represents the total (mean or maximum) heavy metal available for intake.  Gradient's model now assumes that the hand WILL make contact with the mouth each time a laundered shop towel is handled.

Gradient assumes that even though the towel contains a mean total amount of lead (2.83 mg), only 75% of that lead will come in contact with the hands.  That is, only 2.72 mg is available to be transferred from the towel, based on the lead being evenly distributed on the laundered shop towel at 0.0012 mg/cm2.

The next part of the equation is where their assumptions really start to be stretched to the point of implausibility.  Gradient assumes that the hand (single) comes in contact with the 75% of the towel and 13% of the contaminant on the towel is then transferred to the hand.  This is what they call "towel to hand transfer," referenced as "Tt/h" in the equation.

There is nothing wrong with this logic, unless you take issue with the fact that these towels have been washed in hot water, with soap, and dried under a high temperature. To assume that 13% of whatever contaminants are in the towel can come off onto the hands is a bit of a jump here. (see post)

OK, so let's give them a 13% transfer from the towel to the hand - for now.  The next parameter, "daily hand-to-mouth transfer efficiency" (HTE) is where you really need to stretch your beliefs.

Gradient's model and calculation assumes that each worker that picks up a laundered shop towel will transfer 13% of what is on the towel onto the hand - and then - 13% of what is on the hand will be transferred into the mouth.

So for lead, that amount transferred to the mouth would be calculated as follows:

• 2.72 mg x 0.13 x 0.13 = 0.046 mg

That number, 0.046 mg, is the amount of lead Gradient's calculation determines the worker will ingest when they use one single laundered shop towel.

How did they come up with that second value of 13%?  Read their Study, but I'm going to tell you that its origination does not matter.  What matters is this:

How will the lead on the hands be transported into the mouth?

What other studies have calculated are not important unless they involve workers who use shop towels or some other contaminated material.  How does the hand transfer the contaminant to the mouth?  Gradient assumes that it takes place - and they assume it happens each and every time a worker uses a laundered shop towel.  They call this value in the equation the Hand to Towel Exchange ration (HTE)

Rule Number 5: Always make sure the model and equations reflect reality.

What Gradient says about their HTE value is this:

The HTE transfer is based on estimates of the amount of soil transferred by children from the surface of their hands to the mouth, where it is subsequently ingested, but is adapted for adults, based on a lower HTE value, to be consistent with the lower ingestion rate of adults. (Page 9)

Gradient's assumption is that because children transfer soil from their hands to their mouth, adults will do so as well - but at a lessor rate.  So 13% of the load on the hands will be transferred to the worker's mouth.

Once again I need to ask: How?  How does a worker get the lead off of their hand and into their mouth?

Next Post: Laundered Shop Towels: Finger Lickin' Good!


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Laundered Shop Towels: 4- The red bar and the "three sigma" rule

In my last post I looked at how the concentration of heavy metals used to determine the Load value used in the calculation was derived.

Using the mean concentration derived from highly variable data (Standard Deviation is higher than the mean) biases the "exceedance ratios" to look higher than they really are.

Using the maximum contaminant levels detected to derive an "exceedance ratio" presents a situation that is near impossible to reproduce.  The maximum values they used create exceedance ratios that would never be found in the real world - you know - the world in which the worker holds the baby and is asked "why take the risk?"  That world.

Let's start at the beginning....

The equation Gradient uses to calculate these "exceedance ratios" assumes the following:

The worker will use 12 towels per day, five days a week, for 49 weeks in a year, for 40 years for a total of 117,600 laundered towels.

Source: Leach Presentation at 2011 AHMP conference

Let's assume that Gradient's assumption is reasonable, that a worker could, indeed, come in contact with 117,600 laundered towels over their working lifetime of 40 years.

Let's assume also that each time they use one of these 12 laundered shop towels per day, they place their hand to their mouth and the contaminant on their hand is transferred to their mouth - just like in Gradient's graphic below:

From: Gradient 2011 Paper

Regarding presenting data using the "maximum" level of metals found, the question that should have been asked by the authors is; can we reasonably assume that every one of these 117,600 towels could contain the maximum concentration of contaminants that was detected on the 23 sets of laundered shop towels analyzed?

The answer is unequivocally "no" - you cannot assume that.  It is so astronomically small a chance as to be impossible for this situation to ever take place (would probably have a better chance of getting hit by a falling satellite).  The three authors and Gradient should have recognized this and left it out of their study.  Instead they report it and Kimberly-Clark puts a bow on it and parades it out for all the world's workers to see:

Source

But let's say for the sake of discussion, that the towels could contain, for example, a maximum concentration of lead - reported by Gradient to be as high as 600 mg/kg.  What would be the chance of that happening, based on the mean value and Standard Deviation they reported for lead?

Statistically speaking, if the mean is the average concentration for the population (laundered shop towels), and if the data is normally distributed (bell curve), we would assume that 99.73% of the lead concentrations (low to high) found on a laundered shop towel would fall within three Standard Deviations from the mean ("three sigma" or "3 x SD").

Let's look at the maximum values Gradient reported:

From: Data entered into spreadsheet from Gradient 2011 Study

Notice the values in red?  Those values are more than three times the Standard Deviation from the mean.  These values - statistically - would appear only 0.27% of the time a laundered shop towel is sampled.

A more scientifically valid description of those red maximum values would have been to call them "outliers."  Gradient indicates that they removed outliers, but they used them to calculate the maximum intake values.

Why does this matter?  Well for one thing, statistics play into the equation and model Gradient developed for their Study.  If you are going to use a mean, then you need to use everything related to how that mean was calculated and what the mean states.  This brings forth the concept of the "three-sigma" rule.

Why is that important?  Because if the mean of the population of laundered shop towels is X, then the probability of finding a shop towel with a concentration slightly higher than three times the Standard Deviation becomes less than 3 in 1000 (0.99730).

How would this probability work out in the methodology Gradient has set forth in their model and calculation?

Out of 117,600 laundered shop towels, 352 towels could be encountered in a 40 year span of time with a heavy metal concentration at the maximum just above the concentration at the mean plus 3 x SD.  The further from the mean the lower the probability of seeing that value becomes.

Source

Which brings up the heavy metal contaminant: lead.

Lead is the one heavy metal that Gradient and Kimberly-Clark claim presents an intake risk that is; "3,600 times higher than agency exposure guidelines."

The maximum concentration value Gradient used in their equation to determine the Load is 600 mg/kg.  That concentration is just shy of 4 x SD, which tells us that it has a probability of occurring around one (1) time for every 15,000 towels used - or 8 times in a 40 year time period.

What Gradient and Kimberly-Clark want you to accept as a real risk is that with odds of 1 in 15,000, you - the worker - could reasonably come in contact with a laundered shop towel that exposes you to 600 mg/kg of lead each and every time you pick up a laundered shop towel.   They want the worker to accept that this can be done 117,600 times in a row, for 40 years, to give you a 3,600 times higher exposure to lead than acceptable under California's Proposition 65 lead MADL.

In order to obtain an intake exposure to more than 3,600 times the "toxicity criteria" for lead, a laundered shop towel must contain 600 mg/kg of lead each time it is picked up.  Statistically, with a mean of 100 and a Standard Deviation of 139, the chance of getting a towel with that concentration of 600 mg/kg is 1 in 15,000, unless you don't want to believe their mean and Standard Deviation reported.

Was this a blunder on their part?

Rule Number 2: Always look at the data used.

This maximum intake situation is not probable, not possible, not statistically valid.  And all we have looked at is just the data used to calculate the "load" portion in their equation.

Once again, we could stop right here and hold the Gradient findings presented in the study up as invalid.    Right now, the use of incorrect mean and maximum Load values relegates this paper to inaccurate, misleading, and heavily biased towards a conclusion of elevated risk.

But once again, where's the fun in stopping now?  There is more to influence the calculation of "intake" than just heavy metal concentrations they report are in/on the laundered shop towels.

No wonder Kimberly-Clark and the The Association of the Nonwovens Fabrics Industry (INDA) love this paper.

To reiterate....

• Rule Number 1: Always read the report the findings/recommendations were based on.
• Rule Number 2: Always look at the data used.
• Rule Number 3: Always check the assumptions used to derive the model that drives the conclusion.
• Rule Number 4: Compare apples with apples and oranges with oranges.
• Rule Number 5: Always make sure the model and equations reflect reality.

Next post: Laundered Shop Towels: That's quite a load


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Laundered Shop Towels: 3 - Is it mean to ask for a median?

There are five rules that I would like to put forth regarding any scientific work used to describe something as being bad or good.

• Rule Number 1: Always read the report the findings/recommendations were based on.
• Rule Number 2: Always look at the data used.
• Rule Number 3: Always check the assumptions used to derive the model that drives the conclusion.
• Rule Number 4: Compare apples with apples and oranges with oranges.
• Rule Number 5: Always make sure the model and equations reflect reality.

This includes spending time to scrutinize what I am using to defend my position as well.  Go to the links, read the references I am using and quoting.  Do this not just to keep me honest, but to point out any mistakes I may have made.

I'm only human, and so are the three authors of the 2003 and 2011 Gradient Laundered Shop Towel Study.

Because we are human we make mistakes.  We blunder, we miscalculate, we make poorly reasoned assumptions, we put forth facts that are not properly vetted, we think we know what we're talking about when we really don't, and sometimes we purposely mislead for reasons unrelated to the pursuit of knowledge.

In any case, what we generate and hold out as "Scientific" or "Peer Reviewed" may be used to further a particular way of thinking or an agenda.  It may even be used to help sell disposable shop towels.

Kimberly-Clark's dire warning to workers is based on an "exceedance ratios" which was calculated by Gradient:

"Concentrations of metals in laundered shop wipes can result in exposures (as evaluated using the methodology presented in this report) which exceed toxicity criteria for certain metals."

 "Why take the risk" Kimberly-Clark warns workers who are are currently using laundered shop towels.

Is there a risk?  It all comes down to how exposure risk via a laundered shop towel was calculated - the methodology used to derive the black and red bars shown in Kimberly-Clark's graph:

Source

This graphically illustrates to a reader that the "exceedance ratio" for certain metals is huge, therefore the risk to the worker for adverse health effects, specifically cancer, is equally huge as well.  And in case the graph does not convey that message...:

Source

All of this concern (Google "Laundered Shop Towels") is based on a study performed by a "renowned" company with "expertise" in such studies.  But despite what the Supreme Court may have said, Gradient is not a person who is human.  Gradient did not write this paper and make these assumptions, three humans did.

The contention that a worker should be concerned, that a worker should be presented with a question of why take the risk?, is resting solely on the work performed by three educated and experienced researchers.

If their study's conclusions are valid, it will stand up to scrutiny.  Its assumptions will be judged sound, and its conclusion deemed reasonable.  That's how it works when you put a paper out for publication, even if it will only appear in a trade journal.  And it particularly must stand up to scrutiny when you present it to an association of Environmental Health & Safety Professionals who are in the business of protecting employee health. (1)  You had better be right on this if I am going to change from laundered shop towels to disposable ones.

The reason I spend my free time writing this blog on subjects such as this, is to help me understand what is going on regarding a particular topic.  I am also an EHS educator, a career I am passionate about.  I understand stuff because someone took the time to explain it to me along the way.  So this is payback.

If you Google "Laundered Shop Towels" you will find the first page of search results trumpeting the same message Gradient's study concluded.  Laundered shop towels are deemed bad because these three researchers wrote a paper where they show via a model and calculation where a worker could consume more than 3,600 times the Proposition 65 safe intake level for lead.  One after another, these web sites parrot the same message about "toxicity" and "risk."

And they do so because they have not read the study.  They don't look at the data used, they don't question the assumptions, they can't understand what values can be compared with one another, and they don't stop to ask the fundamental question: does the model and calculation reflect reality?  They assume it is true because Gradient put it out there and these three highly educated and experienced researchers wrote it.  End of story.

In my last post, I showed how Gradient's "Towel to Hand" transfer rate was derived, and how there is no data showing if heavy metals remaining on a laundered shop towel can - or do - transfer to the hand.  That assumption that they do transfer is the foundation behind all the "exceedance values" they calculated.  That assumption is based on other studies that looked at dislodgeable dust and pesticides.  Will a laundered shop towel transfer heavy metals to the hand like pesticide/dust will be transferred to the hand from carpet?

That is an important bit of missing information.  So we are asked to assume the rags behave similar to carpet and the rate of transfer is 13%.  Gradient has nothing to back that up, it's just an assumption - one of many - based on other studies they looked at.

So for the sake of moving forward, and in the absence of any other data, lets assume the Tt/h is 13%.

Gradient claims that the worker's hands will contact 75% of the towel's surface area and the "Load (mg/cm2)" on that 75% of the surface will be transferred onto the hand at an "efficiency" rate of 13% (Tt/h ratio).  If you look at the calculation Gradient uses:

Gradient 2011 Paper

...the amount of heavy metals on 75% of the towel's surface that contacts the hand is reduced by 13%.  Since we are going to assume that the lead on the towel can dislodge onto the hand, we will also assume that up to 13% of the lead on the towel's surface the worker's hand comes in contact with, will now be transferred onto the hand.

The black and red bar graph at the beginning of this post shows the "exceedance ratios" Gradient determined using the calculation shown above.  That calculation spits out an intake based on variables that are derived from assumptions and hard data they use.

The "Intake" Gradient calculated for a worker is based on a contaminant "Load" per towel.  In other words, how much of these heavy metals are on the towel before the employee uses it?  Their model is based on the assumption that the towel is contaminated with heavy metals and that these metals will be transferred to the employee's hand - and then into the mouth (intake).

So the first critical step in this model's calculation is to find out how much heavy metals are available for transfer.  Let's look at the data and the decisions that were made regarding that data.

In the black and red bar graph, it graphically shows the "maximum" risk and "mean" risk that was calculated when compared to "various health-based criteria."

The black bar is based on the "mean" and the red bar is based on the "maximum" concentration of heavy metals detected in/on the rag.  This is important because those bar graphs show how far above an acceptable intake the worker could be exposed to.  That number drives the warning: "why take the risk."

That intake value is dependent on the mean and maximum concentrations Gradient found to be in/on the laundered towel.  Based on these lab reports, the mean and maximum heavy metals in/on a laundered towel are assumed to be available to be transferred (Load) to the employee's hand (Tt/h) and then transferred into the employees mouth (intake).  You need to have intake to have a risk, you need to have transfer to get it into the mouth, and you need to have exposure to a certain amount of a contaminant to determine the degree of risk.  So the mean and maximum heavy metal values Gradient calculated are critical.

Let's look at the mean contaminant concentrations Gradient reported. (Rule Number 2: Always look at the data used).  This table is copied directly from their study.

Gradient 2011 Paper

You see those red arrows I put there?  Those are there to show you which contaminant results had Standard Deviations higher than their mean.  This shows that there is high variability in the data, which impacts the true average - mean - concentration that actually is present.

The concentrations Gradient used to derive the Load are skewed, which means they are not symmetric, Therefore the "mean" concentration was not appropriate to calculate the Load because the data does not behave in a Gaussian (bell curve - normal distribution) fashion.  The mean they calculated has been influenced by a few very high concentrations and is much higher than what would be normally found if you were to sample thousands of towels.

Source

Here is what the EPA has to say about skewed data:

EPA

At this point I am skeptical that the mean values Gradient calculated and reported accurately represent the average concentration of heavy metals that would be found.  I am pretty sure they are too high since the lower end was bottomed out at 1/2 the detection limit.  Look at the range they report for lead.  The 2nd to last column is the US detected range and the last column is Canada.

2011 Study

There are statistical accepted methods to work around this problem of having "hot spot" data influence the average concentration.   This is where a Statistician comes in handy.  To obtain a proper and statistically sound average concentration the median should have been used or the data transformed (e.g., lognormal).  So right there, the first real number plugged in to Gradient's equation - "Load" - is biased higher than what would be found under normal conditions.  How much higher?  That would require the individual data points for each of the 26 different towel's sampled.  I've requested this from Gradient and have not received it as of the date of this post.

The decision to use values that are biased taints the actual results one is looking to find.. If the Tt/h ratio is higher than it most likely is, and the Load is higher than it most likely is, well you can see the problem.  We keep compounding the errors which drives the intake upwards.

But those black bars pale in comparison to how the red bar maximum "exceedance ratios" were calculated.


Next Post: Laundered Shop Towels: The red bar and the "three sigma" rule

Laundered Shop Towels: 2 - A flaw in the model

Here is what Gradient concludes in their 2011 Study:

Metals on shop towels can get onto hands and then potentially be ingested, as evaluated in the 2003 report and as developed in this evaluation.

For typical use of 12 towels a day per person, exceedances of Proposition 65 limits, and US EPA and ATSDR toxicity criteria may occur for antimony, beryllium, cadmium, cobalt, copper, lead, and molybdenum.  Calculated intakes for these metals were up to 3,600-fold higher (based on maximum intake concentration for lead) than their respective toxicity criterion.

Notice the word "can."  Let's look at how that word is defined by Websters:

"be physically able to."

That word "can" is important because it is the basis behind their model, which is as follows:

• Laundered shop towels contain heavy metals - even after they have been washed.
• The heavy metals in/on the shop towels can get onto the hands.
• The heavy metals on the hand can get into the mouth.
• The amount of heavy metals entering the mouth may exceed California Proposition 65 limits, and EPA & ATSDR toxicity criteria.

Here is the graphic from the 2003 Gradient Study on laundered shop towels - their model:

2003 Gradient Study

There are two important assumptions made here by gradient.

1. The metals on/in the towel can be dislodged onto the hand
2. The metals on the hand will be transferred to the mouth each and every time a towel is handled.

These two assumptions are very important in evaluating the validity of the intake values used to determine the exceedance with Proposition 65, EPA, and ATSDR toxicity criteria.

For these posts I am only going to focus on lead since that is the one heavy metal with the greatest exceedance.

Let's look at the first assumption: The metals on/in the towel can be dislodged onto the hand.  Gradient is basing this on the findings from their 2003 Study on the same topic.  Here is what they base this transfer from the towel to the hand on:

For ingestion exposure via hand contact with the laundered shop towels, we estimated transfer of metals from laundered shop towels to hands based on empirical data regarding transfer of pesticide residues from surfaces to hands, data regarding the number of laundered shop towels used daily per person, as well as an estimate of the percentage of the towel surface area that would contact the hand.

The amount of metal transferred to the hand that could ultimately be ingested was based on a hand-to-mouth transfer efficiency, using methodology developed by the U.S. Consumer Products Safety Commission (CPSC) for evaluating exposure to dislodgeable residues on treated wood surfaces

Gradient is basing their intake values on a model that assumes the lead concentration they determined to be present in shop towels can be dislodged from the towel onto the hand.

It is reasonable here to challenge this assumption based on the following:

Is it reasonable to assume that a shop towel that has been washed in hot water, with a detergent, then dried under heat, can dislodge lead onto the hand?

Gradient is basing their model on a CPSC study that looked a dislodgeable reside and used the same value of dislodgement in their calculation for the "Towel to Hand" transfer rate.  You can read how Gradient justifies their value of "13%" by reading the paragraph on towel to hand transfer on page 9 of the 2011 Study.  Here are the studies they looked at:

2011 Gradient Study

The question is (and I think it appropriate) should a comparison be made using transfer rates involving pesticide residue and dislodgeable residues with what could come off of a towel that has been washed with soap, rinsed, and heat dried?

The basis of their model is that heavy metals on the rag can get onto the hand and into the mouth.  If the heavy metals are not transferred to the hand, exposure took place but transport into the worker did not.

Without the ability to show that a towel - washed in soap and dried under heat - can transfer the lead onto the hand, the model is not appropriate and the intake values calculated are erroneous.

This could have, with relative simplicity, been evaluated by Gradient.  If we are looking at the lead coming off the towel, soaking the towel in water or a saline solution would give some idea of the amount of lead that could be dislodged onto a wet hand.  Additionally, the towels could have been handled aggressively by a test subject and the hands swabbed to see what, if any, residue came off the towel.  Both of these methods would have derived a value of lead that would be available to be transferred to the mouth.

Just because you have exposure does not mean you will have a health risk. There must be intake.  In order for the Gradient model to be valid, the lead must be transported from the towel to the hand.  They have not shown this to take place, only showing that dust and pesticide reside can be transported from a soft surface to the hand.

I cannot agree with their findings based on this one condition alone.  But that would make for a pretty short series of posts if I stopped now.  And besides, where's the fun in that?

So let's assume that the necessary assumption that the metals can be transported from the towel to the hand does, indeed, take place.  The next question becomes" Is the transfer rate of 13% of the lead from the towel to the hand valid?

Once again we are back to square one.  If we assume that the towel can transfer the lead to the hand, then we also have to assume that the transfer rate is similar to that found with dust and residue based on the studies Gradient looked at (see Attachment A graphic above).  The value of "13%" was based on:

Several studies looked at multiple compounds and found different transfer efficiencies depending on the compound being evaluated.  Within each study, we averaged the various relevant transfer percentages; they were averaged separately for studies conducted with dry vs. wet hands.  In reviewing the current literature, transfer to moist hands (average 20%) is four times higher than transfer to dry hands average 5%).  Workers are likely to come into contact with RSTs with both dry and moist hands.  Therefore, we averaged the transfers to moist hands and dry hands separately before averaging the two averages, to equally weight the results from both categories.  This value (13%) is more than double the transfer efficiency used in the 2003 evaluation (5%). (1)

In order to move on, one must agree with Gradient's assumption that 13% of what ever is on the washed towel's surface can be transported onto the hand - based on the surface area of the towel the hand comes in contact with.  If you can live with this assumption, then their model holds and a "Towel to Hand" transfer rate (Tt/h) holds true as well.  If you find this particular assumption a bit hard to accept, well you can ignore the rest of these posts and throw their study into the trashcan.  In order for the assertion that lead exceeds an amount by 3600 times, the lead MUST leave the towel and attach to the hand.

That 13% transfer rate is critical in determining the intake they use to compare against Proposition 65, EPA, and ATSDR toxicity criteria.

I contend that the laundered shop towels will not transfer any heavy metals to the skin under normal shop towel use.  Additionally, I contend that any dislodgeable heavy metals, such as lead, that remains on the towel after washing in soap and drying would transfer onto the skin at a rate well below 1%.

Of course I have nothing to prove that contention with.  So it's Bowman "0", Gradient "1"

But not for long.  I have this little thing called "statistics" to help me out in my contention that there is no additional risk to a worker who uses a laundered shop towel.  Unless they were to maybe eat twelve towels a day....but that's for another blog post.

Next post: Laundered Shop Towels:  Is it mean to ask for a median?

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Laundered Shop Towels: 1 - A mountain or mole hill of risk

I recently got back from attending the AHMP's 2011 National Conference in Austin Texas the end of August.  AHMP is an association for CHMMs, CETs, and EHS professionals.  I attended a bunch of well presented presentations, and also presented one myself on Wednesday.

I found myself on Tuesday attending a presentation by Crystal Leach, Ph.D, who is Director of Global Research & Engineering with Kimberly-Clark Professional, titled:

"Evaluation of Potential Exposure to Metals in Laundered Shop Towels"

Which is the basis behind this question posed to workers by Kimberly-Clark:

Source

Because of what was found, according to Kimberly-Clark:

Source

Those red and black bars paint a very dire picture for those workers using laundered shop towels.  So bad is the risk that Kimberly-Clark has a webpage called "the dirt on shop towels" to show workers how bad it is.  Heck there's Mike Rowe on the page holding laundered shop towels!  I'll have to check out what he has to say about all of this later on.  Right now I am interested in the brochure they developed with this ominous warning on the first page:

Source

The question that one should be asking is this: Should workers be concerned about their health if they are using laundered shop towels?  Should we believe Kimberly-Clark, who sells disposable shop wipes, when they inform the worker that "what they don't know" about laundered shop towels "could hurt them?"

Kimberly-Clark will tell you to believe them because:

"Two studies conducted during the last 8 years show that laundered shop towels contain toxic heavy metals even after laundering." (1)

It's not Kimberly-Clark saying this, it's based on two studies.  Independent studies performed by:

"an environmental and risk science consulting firm renowned for their expertise in Toxicology, epidemiology, Risk Assessment, Product Safety, Contaminant Fate and Transport, and Environmental/Forensic Chemistry." (1)

According to the abstract for the presentation by Crystal Leach, that firm, Gradient:

"undertook analysis of laundered shop towels, and concluded that, even after commercial laundering, the towels studied retain elevated levels of metals. Estimated metal intakes were compared to the California Environmental Protection Agency’s (CalEPA) Proposition 65 regulatory limits for cancer or reproductive effects as well as to various health-based criteria, including those from the U.S. Environmental Protection Agency (U.S. EPA) and the Agency for Toxic Substances and Disease Registry (ATSDR), a federal public health agency of the U.S. Department of Health and Human Services. The Gradient study finds that, for the worker using the typical amount of towels per day, average exposure to seven metals (antimony, beryllium, cadmium, cobalt, copper, lead, and molybdenum) may exceed health-based exposure guidelines set by these agencies. For example, based on the calculations discussed in the 2011 Gradient study, a worker may ingest up to 3,600 times more lead on a daily basis than recommended by CalEPA. Excessive metal exposure over time may present a health concern.

So armed with two studies, performed by a renowned company with expertise in such matters, Kimberly-Clark is able to claim that a worker using laundered shop towels may ingest  up to:

"3,600 times more lead on a daily basis than recommended by CalEPA,"  

Kimberly-Clark even provided us CHMMs with this graphic to show what and how it happens:

Source

That's pretty scary stuff.  I mean 3,600 times higher for lead...from a laundered (i.e. cleaned) shop towel?  Wow!

Now the question becomes: Should we believe the findings in the Gradient study that has been submitted for  publication in the International Nonwoven Journal for the Association of the Nonwovens Fabrics Industry (INBA).

Should we believe this study because it was produced by a renowned company with expertise in risk assessment?  Should we believe their findings because they do not "endorse Kimberly-Clark products or marketing materials?"

Gradient would most likely defend this work by pointing out the credentials of the three researchers who authored it.

Grace Greenberg MPH: I can't find any information on Ms. Greenberg, but she appears to hold a Masters in Public Health.

Barbara D. Beck PhD is an expert in toxicology and in health risk assessment for environmental chemicals, especially metals and air pollutants, and is the author of over 100 book chapters and journal articles on these topics. She has performed site-specific and chemical-specific risk assessments, developed exposure and risk assessment methodologies, and has presented the results to different audiences including regulatory agencies, the US Congress, and the public. Before joining Gradient, she was Chief of Air Toxics Staff for US EPA Region I. Prior to that she was a Fellow in the Interdisciplinary Programs in Health at the Harvard School of Public Health. She is at present a Visiting Scientist in the Molecular and Integrative Physiological Sciences Program in the Department of Environmental Health at the Harvard School of Public Health. (2)

Leslie A. Beyer MS is a senior project manager and toxicologist with over 20 years of experience. Her areas of expertise include environmental health, occupational health and safety, litigation support, project management, and risk assessment. Her projects have covered a variety of topics, including substantiation of structure-function claims for dietary supplements; historical toxicology of vinyl chloride, benzene, and lead; and review and interpretation of toxicological and epidemiological literature and data. She evaluates the significance of occupational and residential exposures, conducts health risk assessments for cancer and non-cancer endpoints, and assesses health effects from exposure to environmental chemicals. Ms. Beyer develops strategy and prepares expert reports in support of litigation cases involving product liability and chemical exposures (e.g., MTBE, dioxin, perchloroethylene, ozone, chromium). (3)

Wow...impressive.

So armed with all of this information I find myself at a crossroads.  Should we accept or reject the conclusion that Gradient has put forth?

Heavy metals have been found in laundered shop towels in amounts that exceed health-based exposure guidelines related to cancer and non-cancer related health issues, like reproductive and developmental effects.

Should we accept it based on the reputation of Gradient and the credentials of the three authors?  Or should we look deeper into the study to see how they came up with data that affords Kimberly-Clark the ability to ask workers:

Why risk it?  Who's counting on you?

Well I have looked into it.  I can support my conclusion that there is no additional risk to a worker using a laundered shop towel.  Period.  Should you believe me?  No, not until you read what I am putting forth as my reasons why this study is flawed and their conclusion false.

Are you sure you want to continue on with this endeavor Bowman?  I mean, we got a Harvard Ph.D and former Chief of Air Toxics for EPA Region 1 as one of the authors!  Are you sure about this?

Yeah...I'm sure.


Next Post: Laundered Shop Towels: A flaw in the model.