A multiple-purpose design approach to the evaluation of risks from mixtures of disinfection by-products.

Drinking water disinfection has effectively eliminated much of the morbidity and mortality associated with waterborne infectious diseases in the United States. Various disinfection processes, however, produce certain types and amounts of disinfection by-products (DBPs), including trihalomethanes (THM), haloacetic acids, haloacetonitriles, and bromate, among others. Human health risks from the ubiquitous exposure to complex mixtures of DBPs are of concern because existing epidemiologic and toxicologic studies suggest the existence of systemic or carcinogenic effects. Researchers from several organizations have developed a multiple-purpose design approach to this problem that combines efficient laboratory experimental designs with statistical models to provide data on critical research issues (e.g., estimation of human health risk from low-level DBP exposures, evaluation of additivity assumptions as useful for risk characterization, estimation of health risks from different drinking water treatment options). A series of THM experiments have been designed to study embryonic development, mortality and cancer in Japanese medaka (Oryzias latipes) and liver and kidney endpoints in female CD-1 mice. The studies are to provide dose-response data for specific mixtures of the 4 THMs, for the single chemicals, and for binary combinations. The dose-levels and mixing ratios for these experiments were selected to be useful for development and refinement of three different statistical methods: testing for departures from dose-additivity; development of an interactions-based hazard index; and use of proportional-response addition as a risk characterization method. Preliminary results suggest that dose-additivity is a reasonable risk assessment assumption for DBPs. The future of mixtures research will depend on such collaborative efforts that maximize the use of resources and focus on issues of high relevance to the risk assessment of human health.

Gonadal cysts in spotted gar (Lepisosteus oculatus) from Bayou Trepagnier, Louisiana, USA.

Gonadal cysts of spotted gar (Lepisosteus oculatus), an air-breathing teleost commonly found in Louisiana waters, are described. Fish were collected from two sites: Bayou Trepagnier, a petroleum-contaminated site (30 males and 42 females), and Bayou Traverse, a control site (17 males and 15 females). After fish were evaluated for gross abnormalities, they were necropsied and the gonads, gonadal ducts, and gonadal cysts were evaluated histologically. Multilocular fluid-filled cysts were noted in the testes, or spermatic ducts of four spotted gars from the Bayou Trepagnier. Unilateral ovarian cystadenomas were present in one female from Bayou Trepagnier. No cysts were observed in the gonads of spotted gar from the control site.

Comparison of water quality criteria and health advisories for 2,4,6-trinitrotoluene.

The U.S. Environmental Protection Agency (USEPA) has recently recommended health advisories (HAs) for 2,4,6-trinitrotoluene (TNT). The purpose of this brief article is to present these values so that the reader can compare them with the water quality criteria that have been proposed in another article (M. G. Ryon and R. H. Ross, 1990, Regul. Toxicol. Pharmacol. 11, 104-113). In that article, a water quality criterion of 140 micrograms/liter for TNT in drinking water was proposed, and in the present article the methodology by which USEPA calculated a lifetime HA of 2 micrograms/liter is presented. The reasons why the water quality criterion and the HA differ are discussed.

Comparison of water quality criterion and lifetime health advisory for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX).

The U.S. Environmental Protection Agency (USEPA) has recently recommended a lifetime health advisory (HA) for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The purpose of this brief article is to present the basis for the calculation of the HA so that the reader can compare it with a water quality criterion (WQC) that has been proposed (E. L. Etnier, 1989, Regul. Toxicol. Pharmacol. 9, 147-157). In the earlier article, a water quality criterion of 105 micrograms/liter for RDX in drinking water was proposed, and in the present article the methodology by which USEPA calculated a lifetime HA of 2 micrograms/liter is presented. The differences in the derivation of the WQC and the HA are discussed.