Nearly 1.6 billion lbs. of poultry litter are generated annually as a by-product of the Delmarva poultry industry. Disposal via application to fields as fertilizer results in runoff of poultry litter-associated contaminants (PLACs) into receiving waters. Of particular concern are natural steroid hormones 17 ß-estradiol (E2) and testosterone (T), responsible for gender differentiation and development of reproductive structures. The objective of this research project was to assess the potential for endocrine disruption (ED) in fish populations on the Delmarva Peninsula as a result of agricultural litter application.

The investigation included 5 laboratory and 2 controlled field exposures of fish (Pimephales promelas, Cyprinodon variegatus and Fundulus heteroclitus) to water-soluble PLAC. Laboratory assays involved 21-d exposures of adult male and mixed gender larval/juvenile fish to negative, positive (E2) and solvent (EtOH) control treatments, and to one or several environmentally relevant PLAC solutions. Effects on gonads were assessed histologically and plasma and whole-body homogenate vitellogenin (Vtg) levels were measured as a gauge of estrogenicity. Results were used to determine PLAC lower-effects thresholds. Litter application on research fields allowed comprehensive monitoring of runoff over entire planting seasons. Environmental persistence and transport were investigated by measuring PLAC in litter prior to field application and subsequently in runoff and receiving waters. Controlled field exposures involved caging of mature male P. promelas in surface waters receiving litter-amended runoff.

Laboratory PLAC exposures routinely induced Vtg in male P. promelas with response generally dose-dependent. Induction in F. heteroclitus only occurred at the highest tested PLAC concentration while C. variegatus were unresponsive at any tested concentration. All three species produced considerable Vtg in response to the E2 positive control. Gonadosomatic index was unaffected in adult fish, but gamete maturity appeared inversely related to PLAC concentration. PLAC exposure caused a pronounced feminization in P. promelas exposed as larvae (3 - 24 dph) but not exposed as juveniles (36-57 dph). Steroid concentrations (E2 and T) in field runoff were substantial (up to 350 ng E2/L). E2 in receiving waters had an environmental persistence of weeks to months and in one instance exceeded lower effects thresholds identified in the laboratory. ED was not evident in P. promelas caged within receiving waters. However, exposure in the laboratory to agricultural runoff (frozen and renewed daily) induced substantial Vtg in adult male P. promelas.