Ottr LivfUi^ Ri'\(nines — Human Influences 



41J 



The publication of Sileni Spring (Carson 

 1962) highlighted the potential for 

 dichlorodiphenyl trichloroethane (DDT) and 

 other pesticides that persist in the environment 

 to accumulate in and to harm tlsh. wildlife, and 

 the ecosystems upon which they depend. The 

 federal government responded in the mid- 

 1960's by establishing a multi-agency program 

 to monitor the concentrations of pesticides and. 

 later, other long-lived toxic contaminants in all 

 segments of the environment. 



The U.S. Fish and Wildlife Service 

 (USFWS) participated in this program by peri- 

 odically measuring contaminant concentrations 

 in freshwater fish and birds (Johnson et al. 

 1967). Fish were selected for monitoring aquat- 

 ic ecosystems because of their tendency to 

 accumulate pesticides and other contaminants. 

 The European starling iStiiniiis vulgaris) was 

 selected for monitoring contaminant levels in 

 terrestrial habitats because of its varied diet and 

 wide geographic distribution. Following a suc- 

 cessful pilot study (Heath and Prouty 1967). the 

 wings of hunter-killed ducks were used to mon- 

 itor contaminants in duck populations of the 

 major flyways, and thereby to also provide an 

 assessment of contaminant levels in wetlands. 

 The USFWS maintained this National 

 Contaminant Biomonitoring Program into the 

 1980's, with the objective of continuing the 

 documentation of temporal and geographic 

 trends in contaminant concentrations (Prouty 

 and Bunck 1986; Bunck et al. 1987; Schmitt 

 and Brumbaugh 1990; Schmitt et al. 1990). 



Status and Trends 



During the two decades spanned by USFWS 

 contaminant monitoring, the use of persistent 

 insecticides such as DDT was greatly curtailed, 

 and concentrations in fish and wildlife declined. 

 In the environment. DDT breaks down gradual- 

 ly into several different toxic metabolites, of 

 which dichlorodiphenylethylene (DDE) is the 

 most stable and most toxic. A downward trend 

 was clearly evident for DDE in all three net- 

 works (Fig. 1), indicating that the total DDT 

 burden in North America declined. In fish. 

 DDE increased from about 70% of total DDT in 

 1976 to about 147c in 1986 (Fig. 2). 



As existing DDT is metabolized, DDE 

 increases proportionally if DDT inputs are 

 reduced: the proportional change evident in fish 

 therefore provides additional evidence of 

 reduced inputs to North American ecosystems. 

 A similar trend toward increasing percentages 

 of DDE relative to DDT has been noted else- 

 where (Aguillar 1984), indicating that the glob- 

 al DDT burden is also declining. 



In the United States, the bioaccumulation 



{see glossary) of DDT led to eggshell thinning 

 in fish-eating birds such as the bald eagle 

 {Haliaeelus leucocephalus). The resulting 

 decline in recruitment of young to bald eagle 

 populations caused the near extirpation and sub- 

 sequent listing of this species as endangered in 

 the conterminous states (Federal Register 

 1978). The downward trend of DDT concentra- 

 tions docuinented in fish, starlings, and duck 

 wings (Figs. 1 and 2) was paralleled by declin- 

 ing DDE concentrations in bald eagle eggs, and 

 eagle eggshell thickness increased (Wiemeyer 

 et al. 1993). Corresponding increases in recruit- 

 ment have led to bald eagles repopulating many 

 areas (Fig. 2), and reclassification of the bald 

 eagle from endangered to threatened has been 

 proposed for most of the conterminous states 

 (Federal Register 1994). 



In addition to the effects of DDT and its 

 metabolites on eggshell thickness, these com- 

 pounds, as well as PCBs (polychlorinated 

 biphenyls) and other contaminants, are reported 

 to interfere with other reproductive and matura- 

 tion processes in fish and wildlife (e.g.. Fry and 

 Toone 1981). Although overall concentrations 

 have declined, residues of DDT, other insecti- 

 cides, and PCBs remain widespread, and prob- 

 lem areas are still evident. In the United States, 

 concentrations of DDT (mostly as DDE) remain 

 highest in fish and wildlife from areas in the 

 South, Southwest, and Northwest where DDT 

 was used to protect cotton and orchards from 

 insects; in the Northeast, where it was used to 

 control mosquitos; and near former centers of 

 DDT production and formulation. Areas affect- 

 ed by former production centers include north- 

 ern Alabama, near the former Red Stone 

 Arsenal — now Wheeler National Wildlife 

 Refuge (O'Shea et al. 1980); and the Arkansas, 

 Tombigbee, Alabama, and Tennessee rivers 

 (Fig. 31 



Concentrations of other persistent insecti- 

 cides that are no longer in widespread use, such 

 as heptachlor, dieldrin, endrin. and chlordane. 

 have also declined in all three networks (Prouty 

 and Bunck 1986; Bunck et al. 1987; Schmitt et 

 al. 1990). Nevertheless, residues of chlordane 

 remain sufficiently high in fish from some areas 

 of the Midwest to warrant the issuance of 

 human consumption advisories by state health 

 agencies. Concentrations are also high in 

 Hawaii, where chlordane and other chemically 

 similar compounds were used against termites 

 and agricultural pests, as they were in the 

 Midwest. 



Chlordane is a mixture of structurally simi- 

 lar compounds that decompose at different rates 

 over time. The composition of the chlordane 

 mixture present in fish has changed during the 

 1980's in a manner indicative of an overall 



Persistent 

 Environmental 

 Contaminants 

 in Fish and 

 Wildlife 



by 

 C.J. Schmitt 

 CM. Bunck 



National Biological Service 



— 

 70 



75 80 



Year 



85 



D 



0.4- 



Amencan black ducks, 

 Atlantic Flyway 

 Mallards, Atlantic Flyway 

 lylallards, Mississippi Flyway 

 Mallards, Central Flyway 

 Mallards, Pacific Flyway 



74 76 78 80 82 84 

 Year 



Fig. 1. Mean concentrations of 

 DDE in U,S, Fisli and Wildlife 

 Service monitoring networks: (a) 

 fish and starlings and (b) flyway 

 populations of mallards and 

 American black ducks. 



