Mammals

Among mammals, effects on wildlife probably due to the exposure to POPs have been reported for marine - fish-eating - and flying mammals. In bats, a few studies have been produced that clearly demonstrate the role oflipids in the vulnerability of organisms. The principal effect determined on wild specimens was the mortality among migrating adults exposed to DDE. Starvation was induced by experimentation to stimulate the mobilization oflipid reserves for energy requirements, which is one of the conditions typical of migrating organisms. Before the experiment on field organisms, low levels of DDE residues in brain were identified. After induced exercise, the organisms died and the brain concentration increased considerably. Among marine mammals, in the 1960s and 1970s, similar to birds of prey, the ringed (Phoca hispida) and gray seal (Halichoerus grypus) populations of the Baltic Sea declined. The fertility of both species was reduced to c. 20% and the cause was in uterus abortion or fetus mortality. A further dramatic effect ofthe damaged uterus was the absence of further pregnancies. The damage was probably due to the effects ofpersistent pollutants on the adrenal cortex, a syndrome called hyperadrenocorticism. Among other symptoms, a large part could be attributed to the suppression ofthe immune system. In general, these effects coincided with changes in the POP concentrations in the areas of concern. However, among the considered chemicals, metabolites of DDT or PCBs seem to be primary responsible, due to their bioaccumulation in the adrenal cortex. In the 1990s, mature female Baltic Sea gray seals appeared to recover the original reproductive potentiality and this recovery appeared to be linked to the reduction of POP emissions in the Baltic Sea waters. The situation for ringed seals is very different, with occluded uterus still occurring (possibly due to the lifespan of the seals which started previously when POP levels where higher). Similarly, the population of American mink (Mustela viso), a fish-eating mammal, was severely impaired in the same period, and these effects have been confirmed in laboratory, where its reproductive capacity has been demonstrated to be disturbed by low concentrations of dioxin-like PCBs. Reproductive disturbances, probably due to toxic contaminants, have also been observed in common seals Phoca vitulina on the Dutch coast and in Californian sea lions Zalophus californianus. The population of common seal Phoca vitulina in the western part of the Wadden Sea, the Netherlands, declined sharply. Comparative studies on tissues of seals from the western and northern parts of the Wadden Sea showed that the PCBs were the most probable cause of reduced production of pups. PCB pollution predominantly is from the Rhine. Studies performed on laboratory mammals provide evidence of adverse effects of TCDD on male and female offsprings of pregnant dams. The effects associated with the lowest exposure concentrations span from a reduction of sperm count to a feminized sexual behavior in the male offsprings.

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