Assessing Human Exposure
TCE and PCE were clearly present in the the water from Wells G and H in 1979, but it was not known when the contamination began or how severe it had been over the years leading up to 1979. Jimmy Anderson and several other children had been diagnosed with leukemia prior to 1973. If TCE or PCE were responsible, they would have had to have been present in the water prior to that. The exact course of event was unknown, but the models developed by hyrdogeologists suggested a plausible time course for contamination of the wells.
At the time, very little was known about these chemicals, and they were not known to cause childhood leukemia. Investigators would have wanted to find out as much as possible about these chemicals, including how they behave in the environment, their toxicity, how humans may be exposed, and who may have been exposed. Much of what is now know about TCE and PCE was learned after Woburn (and in some cases because of Woburn), but if you were confronted with a similar problem today, you could investigate these chemicals by considering several important aspects of exposure assessment.
Refer to the Exposure Assessment module (link) first, and then apply what you have learned to these chemicals.
Fate and Transport
The fate and transport describes how a particular chemical will behave in the environment or media and how or if it will come into contact with humans. Understanding the media in which an agent is found will allow you to understand the ways in which humans may be impacted. In Woburn, the chlorinated solvents (TCE and PCE) were discharged, or dumped, into the soils. The solvents were transported by rainwater into the groundwater which discharged into the Aberjona River. The chemicals remained in their original forms, but there was some degradation in the groundwater to a chemical called vinyl chloride, a known human carcinogen. The groundwater was used as the drinking water source for many Woburn residents.
Read more information about TCE in the environment.
The toxicity of an agent or chemical describes how poisonous it is. Since there are many different endpoints, or health effects, that may result from exposure to a particular agent, it is important to consider all possible health effects that have been identified for that agent. From the inventory of chemicals identified in Woburn, you would want to consider the toxicity of the chlorinated solvents: dichloromethane, trichloroethylene (TCE), and perchloroethylene (PCE) on the basis of the available toxicity information and concentration in drinking water. Two good sources of information on the toxicity of individual chemicals are ATSDR and IRIS. Explore these web sites for information regarding TCE.
You can also find out how TCE is classified by IARC by searching the IARC web site.
The amount of a hazardous agent present in the media of concern should be considered, as the risk of developing a health effect is a function of both the amount and toxicity of the chemical.
In 1979, Wells G and H were tested and found to be "heavily contaminated" with TCE. TCE was measured in Wells G and H at levels of 267 ppb and 183 ppb, respectively. This was much higher than the federal maximum contaminant level at the time.
Primarily the residents of the neighborhood East Woburn were using contaminated water. These residents included adults, pregnant women, and children. The greatest leukemia risk was in children whose mothers drank contaminated water during pregnancy. Fetuses and children are particularly sensitive or vulnerable to the effects of certain agents.
Routes of Exposure
How humans are exposed is important to consider, as agents of concern may have different toxicities depending on the routes of exposure. In Woburn, the residents were exposed to chlorinated solvents by drinking the contaminated water, inhaling the vapors of the solvents while bathing and showering, and dermally contacting the solvents while bathing and showering.
Exposure Duration and Frequency
It is important to determine the frequency and duration of exposure to an agent. Toxicity is a function of several factors including how long exposure occurs (duration) and how frequently the exposure occurs during that time period. In general, the more frequent the exposure, the greater the possibility that adverse health effects will occur on the largest number of people. Similarly, the longer one is exposed to a toxic chemical the more likely that person is to experience health problems. We would be interested in finding out how long the companies in Woburn have been in operation and how long they have released these chemicals. We also would like to know if the releases occur slowly and consistency, or in periodic, heavy bursts.
In Woburn, the residents were exposed to solvents in drinking water several times daily while drinking, bathing, and washing dishes. Thus the frequency is represented here as several times per day, or daily. If the vapors were present in the homes from either an indoor or ambient source, then the inhalation exposure would be continuous.