DETERMINING RISK Long Island is one of a handful of areas in the US dependent solely on aquifers for its drinking water supply. The most serious threat to this supply is contamination by synthetic organic chemicals. There is increasing concern about the effects of these chemicals on human health. Many are believed to be toxic, carcinogenic, teratogenic or mutagenic. The most troubling health problems brought about by synthetic organic chemicals result from long-term low-level exposure. Exposure at these chronic levels is most peturbing to accurate health risk assessment. At present there are no drinking water standards or guidelines that estimate true risk to public health for most synthetic organics found in groundwater. This is due, in part, to problems associated with assessing the health impact of long-term, low level exposure to known or suspected carcinogens. Little is known about the health effects of chronic low-level exposure. The latency period for cancer which can range from 10 to 40 years, presents complex problems for valid epidemiological studies. The monitoring of subjects and control of variables is virtually impossible. In addition, water is rarely contaminated by only one chemical. Synthetic organic chemicals can react with one another or with naturally occurring compounds to produce other dangerous compounds. Animal testing is generally used as a basis for health risk assessment. The EPA uses mathematical models to estimate the statistical risks to individuals exposed to small concentrations of given chemicals over time. Federal agencies regulate guidelines on the basis of 1 x 10 ^6 or one in a million risk.
ESTIMATE OF CANCER RISKS (per million people from lifetime consumption of water containing 1 ppb of a given chemical)
A shallow private drinking water well near an industrial area is found to be contaminated with BENZENE and VINYL CHLORIDE. These two synthetic organic chemicals are known human carcinogens. Laboratory tests find concentrations of 202 ppb for the Benzene and 300 ppb Vinyl Chloride. You need to estimate the health risk (chances of acquiring cancer) to an individual who drinks this water throughout their lifetime.
PROCEDURE
1. Look up the estimated cancer risk for Benzene on the table above. 2. Divide the estimated cancer risk by 1 x 10 ^6 to determine the estimated cancer risk for individual lifetime consumption. 3. Multiply the concentration of Benzene in the drinking water by the estimated cancer risk for individual lifetime consumption. This value represents an estimate of the chances of an individual contracting cancer if they drank the contaminated well water throughout their lifetime. 4. Repeat steps 1-3 for the Vinyl Chloride. 5. Assuming the effects of these two chemicals is additive and not synergistic or antagonistic, add the two estimates together to get the estimate of the chances of an individual who regularly drank the water of developing cancer.
