Before beginning this post we at OTO want to express our deepest sympathies to the individuals and families who experienced losses in the wake of the horrible Boston Marathon bombing.  We also want to extend our gratitude to the medical teams that helped the injured and to our local, state and federal law enforcement officers who worked tirelessly to bring order back to the Commonwealth.

PCBs in Soil around Buildings

One of the questions that often come up after soil is tested for PCBs in the vicinity of a building is: why are there higher concentrations of PCBs in the soil right around building foundations?  There has been a tendency for investigators to shrug their shoulders and answer: it must be from the degradation of PCB containing caulk or paint used on the outside of the building.  Frequently there is no direct evidence to support this claim, but it seems like the only reasonable explanation that is consistent with the findings.  Well here is another explanation that might also make sense. 

PCBs in Pesticide Formulations

In the 1950s and ‘60s it was common to treat the soil volume immediately around building foundations with pesticides to control or prevent infestations of soil dwelling insects (like termites, ants etc.).  Solutions of pesticides were pumped into the ground under pressure until the surface soil became wetted.  Among the pesticides commonly used in this way were lindane and several of the other chlorinated pesticides.  Since the chlorinated pesticides were very effective and more persistent in the subsurface environment than other options, they were often the pesticide of choice for this purpose.

Although pesticide registrations are now overseen by the USEPA, before there was an EPA (pre-1970) it was handled by the US Department of Agriculture (USDA).  The USDA has generally had a more “congenial” relationship with farmers and other agricultural enterprises than the EPA has had with farmers and the rest of US industry.  During the period when USDA regulated pesticides it was not out of the ordinary for the USDA to make recommendations on the more effective use of pesticides including pesticides for the control of soil dwelling insects.

One of the ways that pesticides lose their potency (even in the ground) is through the volatilization of the active component into air and via the solublization of the  pesticide into water percolating through the soil.   USDA researchers discovered that the addition of certain oils and/or chemicals to a pesticide formulation prior to its application could inhibit the volatilization and solublization of pesticides thereby increasing the amount of time a single application would remain effective.  Further, it was discovered that one of the very best additives for extending the useful duration of a pesticide applications was polychlorinated biphenyls (PCBs).  PCBs did not modify the pesticide’s mode of toxic action, but they did extend the effective duration of a pesticide application up to ten times over a control application that contained no such additive.

This meant that the addition of a relatively small amount of PCBs to a pesticide formulation could significantly increase the value of a single application.  This obviously presented a significant economic incentive for the inclusion of PCBs into pesticide formulations.  The use of PCBs in this manner was actually encouraged by the USDA because it reduced the total amount of pesticide required to control insects in any given situation.

All that Remains

The last pesticide application that included PCBs likely occurred more than 40 years ago.

While it is possible that some detectable trace of the active pesticide ingredient still remains where it was applied, it is more likely that simple volatilization and the aggressive soil biochemical environment has attenuated the pesticide concentrations so they are too low to measure.  However, it is likely that the PCBs used in that long ago application are still present in the soil and can still be readily measured.

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