system (CNS) effects were the most likely effects to occur from direct contact with waste site chemicals. Hepatic, hematopoietic, renal, reproductive, and CNS effects were the most likely indicators of chronic, low-dose exposure through ingestion.
To date, attention has focused on a relatively small number of chemical contaminants identified at hazardous-waste sites. Many identified or unidentified potential contaminants have received little scrutiny. These uncharacterized pollutants include substances that are not on the ATSDR-EPA list of 100 most hazardous substances, compounds that cannot be identified by standardized or accepted analytical methods, previously unidentified substances that result from in situ transformation processes, and by-products of treatment techniques. MacKay et al. (1989) suggest that large quantities of these potentially toxic compounds may be relatively mobile in the subsurface environment, and a potential exists for these compounds to contaminate groundwater.