United States Environmental Protection Agency

About: United States Environmental Protection Agency is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Population & Environmental exposure. The organization has 13873 authors who have published 26902 publications receiving 1191729 citations. The organization is also known as: EPA & Environmental Protection Agency.

Polychlorinated biphenyls as hormonally active structural analogues.

Abstract: Among the environmental chemicals that may be able to disrupt the endocrine systems of animals and humans, the polychlorinated biphenyls (PCBs) are a chemical class of considerable concern. One possible mechanism by which PCBs may interfere with endocrine function is their ability to mimic natural hormones. These actions reflect a close relationship between the physicochemical properties encoded in the PCB molecular structure and the responses they evoke in biological systems. These physicochemical properties determine the molecular reactivities of PCBs and are responsible for their recognition at biological acceptors and receptors, as well as for triggering molecular mechanisms that lead to tissue response. "Coplanarity" of PCB phenyl rings and "laterality" of chlorine atoms are important structural features determining specific binding behavior with proteins and certain toxic responses in biological systems. We compare qualitative structure-activity relationships for PCBs with the limited information on the related non-coplanar chlorinated diphenyl ethers, providing further insights into the nature of the molecular recognition processes and support for the structural relationship of PCBs to thyroid hormones. Steroidlike activity requires conformational restriction and possibly hydroxylation. We offer some simple molecular recognition models to account for the importance of these different structural features in the structure-activity relationships that permit one to express PCB reactivities in terms of dioxin, thyroxine, and estradiol equivalents. The available data support the involvement of PCBs as mimics of thyroid and other steroidal hormones. The potential for reproductive and developmental toxicity associated with human exposure to PCBs is of particular concern.(ABSTRACT TRUNCATED AT 250 WORDS)

Unusual persistence of DDT in some Western USA soils.

Abstract: Agricultural use of DDT (1,1,1-trichloro-2,2,2-bis (p-chlorophenyl) ethane) was canceled in 1972. By the late 1970's and early 1980's, the National Soils Monitoring Program of the US Environmental Protection Agency (EPA) was consistently finding higher soil residues of the degradate DDE (1,1-dichloro 2,2-bis (p-chlorophenyl) ethylene) than of parent DDT. Similarly, the US Fish and Wildlife Service (FWS) had been finding during the late 1970's that DDT and related compounds had been decreasing in birds throughout the US. During 1984 and 1985, the EPA and the agriculture departments of Texas and New Mexico, in response to the FWS, conducted soil sampling in 13 areas where contaminated birds had been collected. It was agreed that soil samples containing higher levels of DDT than DDE would serve as a possible indicator of illegal DDT use. This was an intensive soil sampling program; over 236 fields were sampled. A controversy developed as to whether high ratios of DDT and DDE might corroborate the accusations of recent illegal use of DDT products. Dell City area soils containing higher levels of DDT than of DDE became classified as suspicious soils. Soils bearing the expected higher level of DDE were dubbed as normal. To resolve the controversy, themore » authors, in 1989, conducted a DDT soil metabolism study with representative samples of the suspicious and normal soils. It was felt that a soil metabolism study could, once and for all, determine if there was, indeed, something unusual about the rate at which the suspicious soils degrade DDT.« less

Sorption dynamics of hydrophobic pollutants in sediment suspensions

Abstract: Sorption of hydrophobic organic chemicals in natural sediment suspensions was found to frequently require extended time periods (days to weeks) for complete equilibrium. Sorption dynamics could be described by a two-compartment model that distinguished a rapid or labile exchange(requiring at most a few hours to achieve) from highly retarded or nonlabile sorption requiring days or weeks to occur. For highly hydrophobic chemicals and high solid concentrations, the labile fraction decreased to 0.1 or less in some systems. The kinetic exchange constant for nonlabile sorption varied inversely with the sorption equilibrium constant. An understanding of sorption dynamics is important in describing the fate of highly sorbed pollutants in aquatic systems.

Perchlorate as an environmental contaminant.

Abstract: Perchlorate anion (ClO4-) has been found in drinking water supplies throughout the southwestern United States. It is primarily associated with releases of ammonium perchlorate by defense contractors, military operations, and aerospace programs. Ammonium perchlorate is used as a solid oxidant in missile and rocket propulsion systems. Traces of perchlorate are found in Chile saltpeter, but the use of such fertilizer has not been associated with large scale contamination. Although it is a strong oxidant, perchlorate anion is very persistent in the environment due to the high activation energy associated with its reduction. At high enough concentrations, perchlorate can affect thyroid gland functions, where it is mistakenly taken up in place of iodide. A safe daily exposure has not yet been set, but is expected to be released in 2002. Perchlorate is measured in environmental samples primarily by ion chromatography. It can be removed by anion exchange or membrane filtration. It is destroyed by some biological and chemical processes. The environmental occurrence, toxicity, analytical chemistry, and remediative approaches are discussed.