A New Method to Assess Past Environmental Exposures: Ecomarker/Surrogates of Past Contamination

Abstract

Where cancer incidence is unusually high, residents often claim environmental pollutants are involved. Ensuing studies consistently prove negative. Most such studies focus on current exposures to pollutants of concern (e.g. breast cancer research recently has focused on magnetic fields, DDT and PCBs.) However, because of cancer's inherent latency period, casual relationships with environmental sources, if present, must be related to past, and not present, exposures, rendering current studies essentially futile. Nevertheless, past exposures are not investigated; mainly because contemporaneous measurements and records generally do not exist. This study is based on the hypothesis that significant causal exposures occurred from polluted drinking water emanating from groundwater leaching off hazardous waste sites decades ago. No current method exists to test this hypothesis. Nor does any scientific method exist for measuring past environmental exposures generally, regardless of the source. This deficiency necessitates developing a new approach to investigate environmental pollutants. This research filled this need by developing and validating a novel method to measure past environmental exposures, using legal records, legally mandated data, and legal methods of hazard assessment. I previously postulated that waste site data could be used to predicate exposure surrogates. I developed a hazard density score, HDS, (the number of hazardous waste sites per square mile), to represent past environmental exposures, and found a significant correlation with breast cancer incidence in NY State's 62 counties. In this study, the HDS was improved, tested and validated as an exposure measurement. A refined surrogate, the chemical contamination index (CCI), reflecting continuous exposure levels to particular chemicals, was also developed and validated. The CCI was derived by comparing the total square footage of waste sites within a water district containing the most prevalent county-wide pollutants with the district's size in square miles, providing an index of the extent of point source contamination generated decades ago, i.e. prior to Superfund (1980); SARA (1986); and local implementation (e.g. 1989). Nassau County, New York, was chosen as the test site area for validation, because it derives all of its drinking water from ground water, has an unusually high incidence of breast cancer, and actual records of past exposure currently exist. The surrogates were compared with chemicals in drinking water wells, on a county-wide and water district basis. The most frequently detected chemicals in waste sites across the county were: perchloroethylene, (PCE) trichloroethylene (TCE), dichloroethylene, (DCE) and trichloroethane (TCA). The same chemicals were found in drinking wells countywide-- in identical order of detection, frequency and corresponding prevalence. Two pollutants, TCE and DCE, infiltrated wells at significantly higher concentration levels than TCA, (by two orders of magnitude.) On a water district basis, a high (86%) correlation existed between DCE in waste sites and heavily contaminated drinking. wells, a moderate correlation existed for TCE/PCE well and waste site levels, and no correlation was found between TCA presence in waste sites and drinking wells. It would appear that DCE found in waste sites infiltrates wells at the highest levels of concentration; TCE and PCE, also found in wells at high levels were related to waste site content - but to a lesser degree, and TCA, while present in high levels in waste sites, did not infiltrate drinking wells in any significant level.