Further studies of the organochlorine content of Dipper Cinclus cinclus eggs: local differences between Welsh catchments

In previous papers, we examined the use of deserted and addled eggs of the Dipper Cinclus cinclus as monitors of the contamination of upland rivers by persistent organochlorines. Here, we examine and interpret differences between the organochlorine content of eggs from adjacent sub-catchments of rivers in Wales. We provide information particularly on individual polychlorinated biphenyls (PCBs), for which few data are available on wild birds generally. There were no significant differences between catchments in egg concentrations of total PCBs, although two individual PCB chemicals (or congeners) showed significant differences in concentration or incidence of occurrence. PCB congener 118 (2,3', 4,4', 5 Pentachlorobiphenyl) showed a reduction in concentration on a SW—NE gradient through south and mid-Wales reflecting possible sources in the coastal industrial belt. However, significantly elevated concentrations in Irish eggs suggest the possibility of more remote origins to the west. PCB 101 (2,2,4,5,5' Pen...