INTERANNUAL AND INTRAANNUAL VARIATION IN THE OCCURRENCE OF ORGANOCHLORINE PESTICIDES, POLYCHLORINATED BIPHENYL CONGENERS, AND MERCURY IN THE EGGS OF A RIVER PASSERINE

Failed eggs were collected from the nests of a river passerine, the di pper Cinclus cinclus, in Wales and southwestern Ireland during 1988-19 92 and analyzed for up to 24 pollutants including 15 individual PCB (p olychlorinated biphenyl) congeners. Most pollutants showed significant changes from year to year in their incidence of occurrence and concen tration, in some cases by over an order of magnitude. Individual PCBs varied to the extent that eggs were dominated by different congeners i n each of three different years. Most trends were not uniform, excepti ons being significant and progressive increases in the incidence and c oncentrations of HCB (Hexachlorobenzene) and gamma HCH (lindane). Such marked yearly changes reflect the generally small pollutant concentra tions recorded, in which slight fluctuations in absolute terms were pr oportionately large relative to background levels. Despite inter- and intra-annual change, dipper eggs showed differences in concentrations of DDE (a metabolite of DDT) and mercury between Wales and Ireland. Eg gs also revealed a locality with large PCB concentrations, subsequentl y related to a point source. We conclude that dipper eggs are useful i n indicating spatial patterns in organochlorine pesticides and PCBs, b ut will only detect temporal trends if they are pronounced and sustain ed.