No KCAL9, that's not what the results mean. Part 4

Okay Bowman, you are confusing me.  How can 101 mg/kg of lead in the soil possibly make it a hazardous waste, but 400 mg/kg in the soil make it acceptable for children to live at?

That don't make no sense!

What makes a physical solid material a hazardous waste for lead is based on the idea that if the lead leaches out at or above 5 mg/L it could get into the groundwater and be consumed above the maximum contaminate level (MCL).

The STLCs and TTLCs, originally proposed in 1978, were intended to identify those wastes that “pose a substantial threat to human health and the environment if not disposed in a controlled and systematic manner.  ...the STLC for lead focused on ingestion of drinking water as the route of exposure, considering the exposure pathway of drinking water derived from groundwater or surface water. The STLC was developed by applying a 100-fold attenuation factor to the maximum contaminant level (MCL) for lead, which was 50 µg of lead/L of drinking water at the time the threshold was developed. (Page 4-4)

What makes soil containing less than 400 mg/kg of lead "not hazardous" is based on a risk assessment related to children and the concentration of lead in the blood.

The idea that 5 mg/L of lead leaching from soil is hazardous is archaic. But it is how the regulations require a determination of "hazardous waste" be met.  Would soil that leaches out 5 mg/L of lead create a hazard for the public - children in particular - ??  I don't know.  My guess is that based on what we know now, probably not.

But you are more interested in why up to 400 mg/kg of lead in the soil is okay for a backyard where children play.

That value of 400 mg/kg is based on a complex risk assessment, which is based on how much lead would increase the blood-lead level in a child:

Briefly, within the context of the §403 risk analysis, individual risks refer to the risks associated with a young child’s exposure to specified levels of environmental-lead. Once environmental-lead levels were specified for each medium, the model-predicted blood-lead concentration at these levels, along with the assumption that blood-lead concentrations have a lognormal distribution with a specified variability, were used to estimate the percentage of children exposed to the specified set of environmental-lead levels that would have elevated blood-lead concentrations (i.e., at or above 10 µg/dL). 

Then, those sets of environmental-lead levels associated with estimated elevated blood-lead percentages of 1%, 5%, and 10%... The IEUBK model was used to identify soil-lead concentrations associated with these elevated blood-lead percentages (at specified dust-lead loadings), while the Rochester multimedia model was used to identify (wipe) dust-lead loadings associated with these elevated blood-lead percentages (at specified soil-lead concentrations).  (source)

Told you it was complex!

California looks at lead a bit differently than the EPA, which offers even more confusion when trying to understand why.

One of California’s hazardous waste standards is the total threshold limit concentration (TTLC). The TTLC for lead is intended to protect receptors from direct exposure, primarily through ingestion, which is the type of exposure of greatest concern with lead and certain sensitive receptors. The TTLC in use today assumes that 1,000 mg/kg is protective of children likely to ingest soil containing lead. However, as shown by the recently developed health-based screening values for soils at school sites and near residential lead-paint sites, soil-lead concentrations that protect children who are exposed to lead in soil range from 255 mg/kg to 400 ppm, depending upon the model and assumptions used. The models and assumptions used to develop these values consider the most recent information regarding the health effects of lead and the exposure likely to occur.

California lowers that threshold to 80 mg/kg for children:

The Department of Toxic Substances Control’s Leadspread model (DTSC, 2007) was used to estimate blood lead concentrations in children. The Leadspread model considers exposure to lead in soil by three pathways: ingestion, re-suspension and inhalation, and dermal contact. The Leadspread model was queried for the soil lead concentrations that would give rise to a 90th percentile estimate of increase in blood lead of 1 µg/dL using the “goal seek” function in Excel

The point of all this is this.  The lead concentrations Randy Paige found using the XL2 XRF are above 400 ppm.  This is concerning, especially if the California model is correct.

What needs to happen now is to look at the blood-lead levels in these children.  That would indicate the potential for health concerns.

No need to scare people with "hazardous waste."  That's a whole different wacky world that does not apply to these folks living in Vernon near the Exide facility.

tl;dr: Stop saying "hazardous waste"!!


Thanks for reading.

Jeff