Monday, October 10, 2011

Laundered Shop Towels: 14 - Should you believe them?

In my first post on this topic I asked:
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?
I then went on to say:
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.
So here we are after 13 posts on this topic.  I have presented how Gradient came to conclude that there is a risk

Kimberly-Clark sure wants to take Gradient's findings at face value.  What business wouldn't want to show how bad the other option is by claiming:
"Two studies conducted during the last 8 years show that laundered shop towels contain toxic heavy metals even after laundering." (1)
And they get to do that with unabashed glee simply because of a study prepared interdependently 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)
But those ratios Gradient reports in Table 8a have a much different meaning when you look at how they were generated as well as what the comparison is made to:

Let's look at each one of my issues with their model, calculation, and assumptions.  If there is an increase in risk high enough to warrant discontinuing the use of laundered shop towels, it must be supported by the science presented in Gradient's reports.

Gradient claims that the average concentration of lead (the metal with the highest exceedance ratios -Table 8a) in laundered shop towels is 100 mg/kg.  If that average is not correct, then none of the intake values they calculated are correct.

Based on the minimum and maximum concentrations they present in Table 4 of their study, and the standard deviation reported, it is evident that the average Loads they use are skewed to represent a higher concentration of metals than would naturally be found.

The calculated mean - or average - is supposed to represent the true mean of the population.  Based on the high variability in the concentrations they report (as shown by the standard deviation exceeding the mean) it is highly unlikely that the averages they used to determine the Load represent what is actually found on a laundered shop towel.  It is, in most likelihood, magnitudes higher than what would normally be found.

Let's look at an example to illustrate this:

Here are 25 values representing the lowest concentration detected (1.7) and the highest (600) for lead.  All the other numbers are just numbers I came up with.  The numbers in blue represent all the values less than the mean, the numbers in red represent concentrations higher than the mean.  Using these numbers I was able to get close to the mean and standard deviation reported by Gradient.

Since 100 mg/kg is the number Gradient uses to estimate the lead Load on the laundered shop towel, if these were the actual values detected, 22 towels encountered would have a concentration of lead on them less than 100 and three would be above.

In a normal distribution, "100" would be the average encountered. so at the end of the day, after handling 12 shop towels, the load encountered would be around 100.  That's based on a normal distribution, where 100 is in the middle, half lower and half higher.  In my example 92% of the towels encountered have a lead concentration lower than 100.  See previous post on this topic.

I don't know what the actual concentrations for lead are, but I do know that the average of 100 is not a true representation of what is normally found on laundered shop towels.  It is too high based on the standard deviation reported.  This means that the Load for the towel they calculated is too high as well.

Even if the mean concentrations Gradient reports were correct, there is still the issue on whether or not the metals can be dislodged from the towel and onto the hand.  That's the whole purpose of calculating a Load, to see what is available to enter the mouth from the hand.  I discussed that issue in this post, and it is extremely relevant in determining the validity of their intake values.

The fact that an object may contain a high concentration of metals does not warrant concern if those metals can not be transported into the receptor, in this case from the hand into the worker's mouth.  In order for Gradient's model to hold true, metals must come off the towel and onto the hand - Tt/h.  Why Gradient did not look at what, if any, metals could dislodge from the towels is beyond me.  Even Adam and Jamie of the Mythbusters could have figured out a sound way to determine this.  And they're not PhDs!

So I'll call the "Load" and "Tt/h" part of Gradient's calculation:

But let's look at Load from a different angle.  Gradient claims that the intake of lead a worker might encounter on laundered shop towels is "11" times higher than the CalEPA NSRL for lead.  That is, the lead Load is significant enough to bring about 10 additional cancers for every 100,000 workers using laundered shop towels. (We would expect one cancer at the NSRL).  See previous post.

As I showed in that post, 100,000 workers would use 11.8 billion laundered shop towels.  Are you willing to contend that the 25 shop towels Gradient tested represent the Load on 11.8 billion towels?

Not only are the Load values Gradient used in question, but the intake they calculated requires the worker to place their hand to their mouth each time a laundered shop towel is used.  For these exceedance values to be true, a worker must bring their hand (single) to their mouth 117,600 times (12 towels, 245 day, 40 years).  And each time they bring their hand to their mouth, 13% of what is on the hand comes off the hand and is consumed.

Where did Gradient come up with that number of 13%? That number is half the amount of soil a child consumes if all of the soil consumed came from the hands.  Read my post on this for more information on how Gradient derived this.

Why Gradient chose to use a child's hand and not an adults when calculating this transfer efficiency can only be answered by them.  Had they used an adult's hand, the HTE would have been 6%.  But that's still based on a faulty premise that all of the soil consumed by the adult came solely from the hands.

A better - or more sound - method would have been to use CalEPA's hand to mouth calculation (see post). Once again, why Gradient made up their own method for deriving an HTE can only be answered by them.  It does seem odd though, that they would use CalEPA's MADL and NSRL thresholds and not their methodology.  Peculiar.

Based on this, I'll call the "HTE" part of Gradient's calculation "Busted" as well:

And what about Kimberly-Clark's claim:
"Just how far did they exceed these limits? Here’s one example: the study found that a worker using a typical number of shop towels per day can be exposed to up to 3,600 times the health-based exposure limit set for lead." (4th page)
What does that mean, "3600 times?"  That health based exposure limit is the CalEPA MADL for lead, and had Kimberly-Clark been more forthcoming, they would have let the worker know that the value CalEPA uses is based on health of the fetus and is set 1000 times lower than the no observable health effects level described in the literature.  See this post and this post.

What Gradient should have done was calculate potential exposure risk using EPA's method for determining the clean up level of lead in soil, which is also based on the health of he fetus (post).  EPA's "preliminary remediation goals (PRG) are based on the amount of lead intake from soil that would bring about a level of lead in the blood harmful to the fetus. At that blood level concentration of lead, Gradient's intake value exceeds the EPA 'safe" level by 3 times.  Using the more appropriate 6% HTE (based on an adult hand), the exceedance ratio is 1.3 - using all the other assumptions and values used by Gradient.  3600 times higher refers to a value used to determine when signage and notification is not required by a business.

So I'll call Kimberly-Clark's claim in their brochure:

There you have it.  I've shown you theirs...and I've shown you mine.

Should you believe Kimberly-Clark when they state:
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 still conclude that laundered shop towels pose a risk to workers?

You have read my posts and can easily check my sources and work my calculations.  Here is what I think, based on what my research into this matter has shown me:

Which leads me to only one conclusion - Gradient's study and conclusion is....

Next post: Laundered Shop Towels: 15 - Why I spend the effort


Saturday, October 8, 2011

Laundered Shop Towels: 13 - 100,000 workers using 12 laundered shop towels per day

If 100,000 workers using 12 laundered shop towels for 245 days per year for 40 years consumed 15 ug of lead each and every time the 12 towels were handled, we would expect to see one additional cancer as a result of that exposure.

If 100,000 worker using 12 laundered shop towels for 245 days per year for 40 years consumed 168 ug of lead each and every time the 12 towels were handled, we would expect to see how many additional cancers as a result of that exposure?

In my last post, I showed the formula CalEPA uses to calculate the NSRL - No Significant Risk Level - value of 15 ug/day of lead.  Here is how the CalEPA calculates that risk of one in 100,000 for the NSRL:

Source  Page 15

Doing a bit of algebra - I think that's what it's called - we switch the variables around so we can solve for "R"-  which is the cancer risk.
  • R = (0.168 mg * 0.047 mg/kg-day-1) / 70 kg = 1.1E-04 or 1.1 in 10,000 or 11 in 100,000.
See!  11 times, just like Gradient said in Table 8a!

Yes, but think about it for a minute....

What that ratio of "11" represents is this situation:
  • 100,000 workers using 12 laundered shop towels per day for 9,800 days (245 * 40)
  • 11,760,000,000 laundered shop towels containing an average of 100 mg/kg of lead
  • 100,000 workers placing their hand to their mouth 11,760,000,000 times
Let those numbers sink in...check my math, I could have made a calculation error.

Notice what it would take to get 11 additional cancers in 100,000 workers for 100 mg/kg of lead?  11.8 billion laundered shop towels used, 11.8 billion times the worker's hand contacts the mouth.

Here is what ATSDR says about exposure and cancer, just so you can see that my logic is sound on this.
ATSDR extensively reviews literature linking exposure to compounds with cancer. The lowest level of exposure documented to cause any form of cancer in humans or animals is reduced by a safety factor of 100,000, which simply means if 100,000 people were exposed to this amount ofcompound 24 hours, everyday of their lives for 70 years, 1 extra cancer case might be expected above the normal rate of cancer in that population, i.e. 1 case in 100,000 above normal. (1)
The population here is workers.  So if you can honestly envision 11.8 billion laundered shop towels containing and average of 100 mg/kg of lead after being washed in soap and hot water, then dried under heat, a plausible situation, well I've got a bridge for you to buy!  And if you can see each of these 100,000 worker's bringing their hand to their mouth 11.8 billion times, well I've got land in Florida to sell you as well!

That ratio of "11" times higher than the NSRL uses Gradient's values and equation!

What happens if I use lead intakes calculated using more sound values?   In a previous post I made a case for throwing Gradient's equation out...

...and replacing it with CalEPAs hand to mouth equation.

Guideline for Hand-to-Mouth Transfer of Lead through Exposure to Consumer Products: 2011
The CalEPA equation calculates the daily total intake.  The intake is divided by 70 kg (weight of an adult) to derive a mg/kg-day intake value. (See post)
  • Intake = 0.0013 mg/cm2 x 19 cm2 x 0.5 x 1.5/hour x 8 hours =  0.148 mg per work day
  • 0.148 mg per day = 0.148 / 70 kg =  0.0022 mg/kg-day Intake or 2.2E-03 mg/kg-day
Using Gradient's EF of 245 days, an ED of 40 years, and an AT of 25,550 days (70 years) we would modify the CalEPA calculation as follows:
  • (0.0022 mg/kg-day * 245 days/year * 40 years) / 25550 days = 8.4E-04 mg/kg-day
  • 0.00084 mg/kg-day * 70 kg = 0.06 mg-day
Using CalEPA's hand to mouth intake formula, a worker using twelve laundered shop towels per day for 40 years would have a lead intake of 0.00084 mg/kg-day over a 70 year period of time.

Placing that intake into CalEPA's cancer risk calculation, the "R" cancer risk would be:
  • R = (0.06 mg * 0.047 mg/kg-day-1) / 70 kg =  4 in 100,000.
Using Gradient's values - with the exception of the hand to mouth transfer rate - the excess cancer risk from using 12 towels per day containing 100 mg/kg of lead for 40 years is 4 additional cancers per 100,000 workers.

So whatcha think?  

Is 11.8 billion shop towels with 100 mg/kg lead a plausible scenario?  Will 100,000 workers place their hand to their mouth 11.8 billion times?  Is this really an exposure situation where one would ask a worker who is using a laundered shop towel:  "Why risk it?"
As I stare into that baby's eyes I have no problem telling that dad, go ahead and use laundered shop towels. If lead is the baddest metal they found, go ahead and use a laundered shop towel all you want.  Heck, you can even use it while drinking apple juice!

Next post: Laundered Shop Towels: 14 - Should you believe them?


Thursday, October 6, 2011

Laundered Shop Towels: 12 - Everything gives you cancer...except laundered shop towels.

First, a little bit of background on looking at exposure to carcinogens:
ATSDR recognizes that, at present, no single generally applicable procedure for exposure assessment exists, and, therefore, exposures to carcinogens are best assessed on a case-by-case basis with an emphasis on prevention of exposure. (1)
What this means is that we can provide no real method for dose/response when it comes to exposure to chemicals suspected to be carcinogens.  Therefore "0" exposure is recommended.
ATSDR recognizes that estimation of lifetime cancer risks is further complicated when available data are derived from less than lifetime exposures and that pharmacokinetic insights from animal models may be of utility in addressing this issue. (1)
What this means is that we can look at animal models to help us, but we lack data on a lifetime exposure to chemicals (70 years) so our estimates of a cancer risk will be lacking.
The lowest dose levels associated with carcinogenic effects are identified as cancer effect levels (CELs), with the stipulation that such a designation should not be construed to imply the existence of a threshold for carcinogenesis. (1)
Lowest dose found does not draw a line in the sand where below that is "no cancer" and above it is "cancer."
Also, exposures associated with upper- bound excess risk estimates over a lifetime of exposure (i.e., one case of cancer in 10,000 to one case of cancer in 10,000,000) as developed by EPA are presented. (1)
We look at dose in terms of a cancer risk.  CalEPA looks at a risk of cancer as one in 100,000 (10-5):


CalEPA has developed a "No Significant Risk Level" (NSRL) of 15 ug/day for lead.  What this value is used for is to set a "safe harbor" amount for which the business does not have to post a Proposition 65 warning sign.  It assumes that a person could consume up to 15 ug of lead per day (2.14E-03 mg/kg-day) with out a risk of more than 1 additional cancer per 100,000.  15ug of lead dos not assume a "safe" threshold, it is used to establish an amount of lead whereby a Proposition 65 notification is not required.

When Gradient states that lead exceeded the CalEPA NSRL by "11" times:

(Gradient 2011 Report)

What exactly does a ratio of "11" mean in terms of risk?  Here is what ATSDR says about assessing exposure to a carcinogen:
Both exposure and toxicity information are necessary to fully characterize the potential hazard of an agent. ATSDR considers exposure to an agent to be "an event consisting of contact at a boundary between a human and the environment at a specific environmental contaminant concentration for a specified interval of time; the units to express exposure are concentration multiplied by time."  (1)
Gradient assumes that each time a laundered shop towel is handled by a worker - exposure - there will be intake of the metals that remained on the towel after it has been washed.  That intake is also referred to as a "dose" which ATSDR defines as:
"[t]he amount of contaminant that is absorbed or deposited in the body of an exposed individual over a specified time. Therefore, dose is different from, and occurs as a result of, an exposure."  (1)
In order for Gradient's model to be true, contaminants on the laundered shop towel must be deposited onto the hand and the hand must contact the mouth.  The "dose" will be the amount of contaminant on the hand that is transferred into the mouth.

Cancer risk is looked at differently from chemicals that do not contribute to cancer or cause health effects other than cancer.  Gere is what CalEPA says about exposure to carcinogens:
For chemicals that are listed as causing cancer, the "no significant risk level” is defined as the level of exposure that would result in not more than one excess case of cancer in 100,000 individuals exposed to the chemical over a 70-year lifetime. In other words, a person exposed to the chemical at the “no significant risk level” for 70 years would not have more than a “one in 100,000” chance of developing cancer as a result of that exposure. (2)
How does CalEPA calculate that "no significant risk level” for lead?

Source  Page 15

The "theoretical cancer potency" - qhuman - is also called the cancer slope factor.

For lead, CalEPA uses the value 0.047 mg/kg-day-1 (see graphic at the top of this post).  Plugging in this value into the formula:
NSRL = (0.00001 x 70) / 0.47 = 0.0148 mg or 0.0148 * 1000 = 14.8 ug ~ 15 ug (ppb).
In other words, a person exposed to 15 ug (ppb) of lead for 70 years would not have more than a “one in 100,000” chance of developing cancer as a result of that exposure.

If we agree that 15 ug consumed for 17 years would  show more than one additional cancer per 100,000, what would Gradient's intake of 2.4E-03 mg/kg-day (0.168 mg)?

(Gradient 2011 Report)

In other words, if 15ug lead = 1 in 100,000, what would 0.168 mg lead result in?

Guess I'll need to calculate that.  Dang, more math...and I suck at math.  (Note to past self should time travel become a reality: Take math instead of computer programming in Fortran.)

Next post: Laundered Shop Towels: 13 - 100,000 workers using 12 towels per day


Monday, October 3, 2011

Laundered Shop Towels: 11 - Lead, a fetus, and a PPM.

What does the EPA have to say about lead when it develops clean up goals for lead contaminated soil?
In the commercial/industrial setting, the most sensitive receptor is the fetus of a worker who develops a body burden as a result of non-residential exposure to lead. Based on the available scientific data, a fetus is more sensitive to the adverse effects of lead than an adult.
We assume that cleanup goals (preliminary remediation goals or PRGs) that are protective of a fetus will also afford protection for male or female adult workers.
The model equations were developed to calculate cleanup goals such that there would be no more than a five per cent probability that fetuses exposed to lead would exceed a blood lead (PbB) of 10 micrograms lead per deciliter of blood (µg/dL). This same approach also appears to be protective for lead’s effect on blood pressure in adult males.
How much lead in soil consumed is necessary to produce 10 micrograms lead per deciliter of blood?

This is a fair and relevant question, and it relates to the problem with workers using laundered shop towels.

If Gradient is stating an "exceedance ratio" of "591" times the CalEPA MADL, which is the "maximum allowable dose levels for chemicals listed as causing birth defects or other reproductive harm" And the MADL for lead is based on "fetal development," then looking at how much lead consumed is required to produce "10 micrograms lead per deciliter of blood" - an actual quantitative amount of lead in the blood where we expect there will be adverse effects to the fetus above that level - would tell us how much total lead would need to be ingested to bring about that amount of lead in the blood.

Let's look at the variables EPA uses and the values they assigned:

Based on this, the consumption of 50 milligrams (0.050 grams) of soil containing up to 2,240 ppm of lead should be "protective of a fetus will also afford protection for male or female adult workers."

If 10,000 ppm is 1%, 2,240 ppm is 0.2%.  So...0.2% of the soil consumed puts into the blood the amount of lead to achieve 10 micrograms lead per deciliter of blood.

How much total lead would be consumed if 50 milligrams of soil containing 2,240 ppm of lead is ingested?
0.2% * 50 mg = 0.002 * 50 = 0.1 mg of lead
Based on a PRG of 2,240 ppm, EPA states:
A key concept is that a PRG is the average concentration of a chemical in an exposure area that will yield the specified target risk in an individual who is exposed at random within the exposure area.  Thus, if an exposure area has an average concentration above the PRG, some level of remediation is needed. (1)
The consumption of lead, and I am assuming from any source, of less than 0.1 mg per day, would not contribute to more than 10 ug/dl of lead in the blood, which is the amount of lead in the blood protective of a fetus.

What is the amount of lead per kg of body weight?
0.1 mg-day / 70 kg =  0.0014 = 1.4E-03 mg/kg - day
Since lead is the one metal that produced the highest "Exceedance Ratios of Individual Toxicity Reference Values for Exposure via Hand Contact - Typical Use (12 Towels)," what is applicable to lead will also be applicable for all the other lower "exceedance ratios" Gradient reports. (2)


The MADL value of 0.5 ug-day lead is for "safe harbor" reporting to the public.  The EPA's PRG of 2,240 ppm (0.1 mg - day) is the clean up level for soil to yield a specified target risk of less than 10 ug/dl of lead in the blood deemed to be protective of the fetus.  Both the MADL and PRG are based on protecting a fetus but are calculated based on different assumptions.  The CalEPA's MADL assumes 1000 time less the NOAEL is "safe" for a fetus, and the EPA's PRG assumes a blood lead level of less than 10 ug/dL is "safe" for a fetus.

Which one appears to be a bit more sound?

How does the Gradient lead intake compare to the EPA PRG for lead?
0.0043 mg/kg-day (Gradient's intake value for lead)
0.0014 mg/kg-day (based on EPA's PRG of 2,240 ppm lead in soil)
That's an "exceedance ratio" of 3 times the safe lead level consumed which would be protective of a fetus.

Remember, that's based on Gradient's mean lead concentration they reported (post), the transfer of 13% of the lead from the towel to the hand (post), the transfer of 13% of the lead on the hand to the mouth (post), 12 exposures per day, 245 days a year, performed for 40 years.

How does it look if an HTE of 6% is used? (post)
0.0019 mg/kg-day  (Gradient's intake value for lead using 6% for the HTE)
That's an "exceedance ratio" of 1.3 times the safe lead level consumed which would be protective of a fetus.

How does it look if the CalEPA hand to mouth calculation is used? (post)
0.0022 mg/kg-day (CalEPA calculation for lead)
That's an "exceedance ratio" of 1.6 times the safe lead level consumed which would be protective of a fetus.

You may be tempted to tell me "See!  It's still above a safe threshold using any of those calculations!"  For which I will remind you that those intakes are based on a mean lead concentration on the towel of 100 mg/kg.  Go to the report and look at the range of lead concentrations Gradient lists (Table 4 page 7).

Those values also assume that there will be a transfer of lead from a towel that was washed in water with soap and heat dried, equivalent to 13% of the lead evenly distributed on the towel from which 75% of the surface area comes in contact with the hand.

Oh, and it also assumes that this will happen 12 times a day, and that each time the hand will contact the mouth and some value of lead will be consumed.

All of those things must happen in order to get an "exceedance ratio" that is higher than the "safe" threshold.

There is one more thing that needs to be considered as well.  The CalEPA equation calculates the intake per day.  The PRG value of 2,240 ppm is based on exposure to the soil for a year.

In other words, we would expect (assume) a person coming in contact with soil containing 2,240 ppm of lead for one year, to produce a blood level of no more than 10 ug/dL.  That ppm is based on an exposure frequency (EF) of 219 days and an averaging time (AT) of 365 days.

This EPA PRG model assumes that there will not be constant exposure to soil containing lead, but assume there will be 219 days of exposure and 0.05 grams of soil will be consumed each time there is exposure.  Based on this, 2,240 ppm of lead or less is deemed to be protective.

For an exposure period of one day, lead intake during one work day (12 towels in 8 hours) - using CalEPA's equation (see post) - can be calculated as follows:
  • Intake = 0.0013 mg/cm2 x 19 cm2 x 0.5 x 1.5/hour x 8 hours =  0.148 mg per work day
  • 0.148 mg per day = 0.148 / 70 kg =  0.0022 mg/kg-day Intake or 2.2E-03 mg/kg-day
Using Gradient's EF of 245 days and an AT of 365 days (instead of 40 years to be consistent with the EPA lead PRG calculation), we would modify the CalEPA calculation by multiplying the mg/kg intake by 245 and dividing that number by 365.
  • (0.0022 mg/kg-day * 245 days) / 365 days = 0.0015 mg/kg-day or 1.5E-03
Over a 365 day period a 70 kg worker using 12 towels a work day with an average lead load of 100 mg/kg (ppm) would have an average intake of lead of 0.0015 mg/kg-day.

If this same worker was exposed to soil contaminated with lead, the intake of lead would need to be less than 0.0014 mg/kg-day.

Using CalEPAs calculation, Gradient's values, and a 365 day averaging time, the "exceedance ratio" will be 0.0015/0.0014 = 1.07, or 1.1, or 1 = even.  This average amount of lead reported by gradient will produce a blood lead level of less than 10 ug/dL even when 12 towels are used and the worker places the finger and palm to the mouth each time a towel is used.  This is protective of the worker because it is protective of the fetus!

So the question now is: If lead had the highest "exceedance ratio" reported by Gradient, and you are now presented with CalEPA apples and EPA apples to compare Gradient apples with, are you still concerned about laundered shop towels creating any risk of a reproductive health concern for a worker, even a pregnant one?


Cancer!!!  What about the risk of cancer?

Next post: Laundered Shop Towels: 12 - Everything gives you cancer...except laundered shop towels.


Sunday, October 2, 2011

Laundered Shop Towels: 10 - When is an average not average?

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

I think I have presented enough justification to throw out Gradient's  "Intake of metals in laundered shop towels via hand contact" equation:

Instead, I believe the CalEPA equation to be a lot more sound and valid for calculating a hand to mouth intake, even though it uses assumptions I think are a bit of a stretch as well.  Still, we need something to quantitatively estimate an intake so we can look at risk, so this equation will have to do for workers using laundered shop towels.

Guideline for Hand-to-Mouth Transfer of Lead through Exposure to Consumer Products: 2011
The CalEPA equation calculates the daily total intake.  To compare apples with apples and oranges with oranges (Rule Number 4), The intake was divided by 70 kg (weight of an adult) to derive a mg/kg-day intake value (see last post).

I commented on how close the CalEPA method intake values match the values I calculated when the Hand to Mouth transfer efficiency (HTE) rate was changed to a more appropriate 6% for an adult.  But that comparison I made is like comparing apples with oranges.

The CalEPA intake is based on a single uptake event and is used as a threshold to meet the California Proposition 65 "Safe Harbor" designation.
A business has “safe harbor” from Proposition 65 warning requirements or discharge prohibitions if exposure to a chemical occurs at or below these levels. These safe harbor numbers consist of no significant risk levels (NSRL) for chemicals listed as causing cancer and maximum allowable dose levels (MADL) for chemicals listed as causing birth defects or other reproductive harm. (1)
As long as a business can keep the exposure below the NSRL or MADL (whichever is lowest) the business does nor have to post Proposition 65 warnings.  The assumption here is that below these levels there would be little risk for cancer or reproductive/birth defects.  What it does not imply is that above those values there is risk.  Risk is related to dose, the lower the dose, the lower the risk.  NSRLs and MADL attempt to draw a line in the sand - one side is "no risk" and the other side is some.

The problem with the Prop 65 notice is that it does not communicate a degree of risk, only that there is risk. One cancer in 99,998 or one cancer in 98 gets the same warning:

Gradient assumes that laundered shop towels that contain concentrations of metals above these thresholds represent risk to the worker, hence the black and red bar graphic I showed in the first post on this topic:


A bit confusing for it shows copper as having a higher exceedance than lead.  Anyway, it is based on information from this table:

2011 Gradient Study

Ignore the maximum intakes they reported - they are statistically impossible to reproduce in a real world situation (see post).  Look instead at the average (mean) intake value for lead, which is the metal that presents the highest exceedance ratio compared to a threshold.

Using the intake equation Gradient developed for hand to mouth exposure, Gradient reports exceeding the CalEPA MADL and NSRL for lead for average laundered shop towel usage by a worker.

Using the CalEPA equation and the same average towel usage and average lead metal loading used by Gradient, I calculate the following exceedance "ratios" for lead:
  • Intake (lead) = 0.0022 mg/kg-day
  • MADL = 0.0000071 mg/kg-day (0.5 ug/day) (2)
  • NSRL = 0.00021 mg/kkg-day (15 ug/day) (2)
This would generate an "exceedance ratio" of:
  • MADL = 309 x
  • NSRL =  10 x
Well, heck, that's lower but still pretty high.  At least that's what one could reasonably conclude when comparing apples with oranges.

Let's look at the "maximum allowable dose levels (MADL) for chemicals listed as causing birth defects or other reproductive harm."  Here is what the CalEPA based the lead "safe harbor" MADL on:

CalEPA 2008 Page 13

That "safe" value of  0.0000071 mg/kg-day is based on fetal development, which is only applicable to a female worker who is pregnant and using the laundered shop towels.  That "safe" threshold - MADL - is not applicable to a male worker's intake using the same laundered shop towels.

Let's look a bit closer on how that MADL for lead is calculated.
The MADL is the level at which chemicals listed for reproductive toxicity would have no observable effect assuming exposure at 1,000 times that level. (3)
What is the " no observable effect" level?
No-observed-adverse-effect level (NOAEL): The highest tested dose of a substance that has been reported to have no harmful (adverse) health effects on people or animals. (4)
No-Observed-Adverse-Effect Level (NOAEL)—The dose of a chemical at which there were no statistically or biologically significant increases in frequency or severity of adverse effects seen between the exposed population and its appropriate control.  Effects may be produced at this dose, but they are not considered to be adverse. (5: Page 526)
Neither ASTDR nor IRIS identify a NOAEL for lead,  instead they use a blood lead level as a "safe" dose.

So if we assume that the lead MADL is based on an effect to the fetus, and we assume that the lead MADL of 0.5 ug-day is 1000 times lower than the NOAEL, the NOAEL used by CalEPA must be 500 ug-day (0.5 x 1000 = 500).  I can find nothing on how CalEPA derived the value "0.5 ug-day" other than this and this.

A NOAEL of 500 ug-day is equal to 7.14 ug/kg-day or 0.007 mg/kg-day (based on 70 kg body weight).  0.007 = 7.0E-03

Gradient reported an average "typical use" intake for lead of 4.2E-03 (Table 8 Page 13).  Even using all of Gradient's assumptions and their intake formula, the intake they report is below the No-observed-adverse-effect level used by CalEPA (7.0E-03).  An average use of 12 towels per day for five days a week, for 245 days per year for 40 years falls below the lowest concentration reported to show no adverse effects.

Still not convinced that these laundered shop towels pose no increase of risk to a worker, even a pregnant one exposed to a mean concentration of lead at 100 ppm?  Well, let's look at it another way.

What is the amount of lead in soil that would be considered to present a risk for a person who ingests 50 mg of soil each day for a total of 219 days in a year?

In other words, under certain assumptions, what would the clean-up level for the lead in the soil be?

Next post: Laundered Shop Towels: 11 - Lead, a fetus, and a PPM.


Saturday, October 1, 2011

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

The equation Gradient has developed to calculate worker intake of metals, such as lead, is based on a number of assumptions.

Not only do we have to accept the mean concentrations Gradient reports for these metal contaminants on the laundered shop towels, but we are also asked to assume that 13% of those contaminants will be transferred from the towel to the hand after the towel had been washed with soap and heat dried.

On top of this, as my last post described, Gradient makes the assumption that each time a laundered shop towel is used, the worker will place his hand to his mouth and 13% of the contaminants on the towel will be transferred to the mouth - intake.

Even if you accept Gradient's intake equation, it is difficult to accept the values they assigned for the assumptions used.

In my last post I detailed why the HTE of 13% Gradient uses is incorrect and an HTE is more appropriated since it involves calculating the HTE using both an adult soil consumption value and an adult hand.

Recalculating the intake values using an HTE of 6% still shows some metals to be above regulatory standards.  This is primarily due to the inappropriateness of calculating the HTE as a ratio of daily soil consumption to amount of soil found on both hands - as was discussed in my last post.

There is a more appropriate way to go about figuring out a hand to mouth transfer, which once again brings up:
Rule number 5: Always make sure the model and equations reflect reality.
Here is how CalEPA looks at lead intake from direct hand to mouth contact, which is the model Gradient should have used to calculate the intake of metals - such as lead - from laundered shop towels.

Source Page 6
Gradient instead calculates a lead intake over a worker's entire working lifetime of 40 years, whereas CalEPA calculates it on a single contact performed i number of times (events).  According to CalEPA:
There can be multiple hand-to-mouth contacts during the use of a given consumer product.  Thus the total direct lead intake via the use of a given consumer product will be the sum of intake from each contact i during product use.
CalEPA modifies the equation above as follows:

Source Page 6
Let's look at how CalEPA calculates the values for these parameters in their equation:

Source Page 11

                                     Surface area (SAD)
Source Page 12
                                    Contact frequency (λD) = Frequency
                                    Exposure Duration (t) = Time

Lhand-D can then be calculated as follows:

Note: To keep consistent with other values used (see below), the surface of the front of the hand will be calculated as 840 (total surface area of both hands) * 0.5 (for one hand) * 0.5 (for the front of the hand).  Thus, the surface area for the front of one hand will be: 210 cm2.  In my previous "fun with graph paper" post, I estimated the surface area to be 188 cm2.

If Lhand-D is:
The lead loading on the part of the hand touching the mouth (not the loading of the whole hand), in units of weight per surface area (e.g., mass of lead per surface area of the fingertip, μg/cm2).
Assuming that 13% of the 75% lead load on the laundered shop towel is transferred to the hand:
  • 0.00127 x 2268 x 0.75 x 0.13 = 0.28 mg
  • 0.28 mg / 210 cm2 = 0.0013 mg/cm2 or 1.3 ug/cm2
 The "part of the hand touching the mouth" or SAD, is calculated as follows: 
Assumed for workers in occupational settings that the surface area of the hands contributing to the hand-to-mouth exposure pathway was 5% of the palmar surface of the hand, or 10 cm2.
Here is what I found in an earlier version of this CalEPA Lead document:

Source 2008

For this post, I will use the adult male SAD of 19 cm2.

Fdirect will be 50% (as per CalEPA)

Contact frequency (λD) will be 1.5 towels per hour (based on 12 laundered shop towels per 8 hour shift)

Exposure Duration (t) will be an 8 hour work shift.

For an exposure period of one day, lead intake during one work day (12 towels in 8 hours) - using CalEPA's equation - can be calculated as follows:
  • Intake = 0.0013 mg/cm2 x 19 cm2 x 0.5 x 1.5/hour x 8 hours =  0.148 mg per work day
  • 0.148 mg per day = 0.148 / 70 kg =  0.0022 mg/kg Intake or 2.2E-03
That's how CalEPA would calculate the intake based on a mean lead concentration of 100 mg and a towel to towel transfer efficiency of 13% - which are the same values Gradient uses in their equation.

Here is how the CalEPA method and equation stacks up against the Gradient equation and assumptions for the metals they reported with concentration exceedance ratios.

CalEPA Formula source

Notice how the CalEPA's equation produces an intake very similar to the values Gradient calculated for cancer intake.  Interesting.

Now lets look at the CalEPA method using an HTE of 6% (see post):

Notice how the CalEPA intake is very similar to the intake values obtained using Gradient's equation with an HTE of 6%.  Interesting.

The question you should now ask is: What equation more accurately estimates the intake if the assumptions used are valid?

I say we go with the CalEPA equation.  Now all we need to focus on will be the assumptions regarding the average load on the towel, the towel transfer efficiency, and the number of laundered shop towels used per day by a worker.  Oh yeah, we will also need to look at the respective "toxicity criteria" these intakes were compared to and how Gradient went about "evaluating the magnitude of the exceedances."

Next Post: Laundered Shop Towels: 10 - When is an average not average?