The Effects of Polychlorinated Biphenyls on Birds

SummaryPolychlorinated biphenyls [PCBs] are chlorinated hydrocarbons which have been used in a variety of industrial applications ranging from consumer plastics to heat exchangers. More than thirty years of the wide use of these persistent materials have resulted in an apparent ubiquitous distribution of PCBs in the global ecosystem at minute concentrations [parts-per-billion], The recent development of analytical techniques with greater sensitivities and specificities, and the ensuing recognition of PCBs in the environment have produced a concern for the influences of PCBs on biological systems and for their importance relative to food safety and environmental health. Further problems occasioned by a number of accidental leaks of PCBs into animal feeds have focused attention on animal agriculture, especially commercial poultry production.Controlled experiments with the chicken have demonstrated that high levels of PCBs can be toxic, causing growth depression, reduced efficiency of feed utilization and mortality with characteristic pathological signs. Studies have shown that the egg-laying chicken is most sensitive to PCBs, lower levels of which can interfere with hatching of the progeny of exposed breeder hens. PCB responses are dose-dependent; controlled experiments indicate that breeding hens can be exposed daily to as much as 0·1 mg per kg body weight without noticeable losses in hatchability. Thus, dietary levels less than 2 ppm are safe for breeder hens; much higher levels can be tolerated if exposure is limited. Experimental evidence shows that the minute concentrations [parts-per-billion] of PCBs detected in environmental materials in various parts of the world represent no threat to the reproductive fitness of birds.