Brains of Native and Alien Mesocarnivores in Biomonitoring of Toxic Metals in Europe

Abstract

Mercury (Hg), lead (Pb) and cadmium (Cd) are involved in mammalian brain damage. However, little is known about Pb and Cd brain levels in wildlife that reflect the geochemical background. The aims of the study include the estimation of Hg, Pb and Cd concentrations, and the determination of relationships between these elements in the brains of 94 mesocarnivores. Road-killed or hunted animals were obtained from north-western Poland near the Polish-German border. The investigation covered the native Eurasian otter Lutra lutra, badger Meles meles, pine marten Martes martes, beech marten M. foina, European polecat Mustela putorius, red fox Vulpes vulpes, and alien species: feral and ranch American mink Neovison vison, raccoon Procyon lotor and raccoon dog Nyctereutes procyonoides. Depending on the diet and environmental pollution, the carnivore brains accumulated toxic metals in varying amounts. The highest median Hg levels (in mg/kg dry weight, dw) were found in the piscivorous Eurasian otter and feral mink (2.44 and 3.96), Pb in the omnivorous raccoon (0.47), while Cd in minks (~0.06). We indicated that Pb-based ammunition is a significant source of the element in scavengers from hunting area, and we also found a significant correlation between Pb and Cd levels in the fox brain. Finally, this study is the first to suggest background levels for brain Pb and Cd in mesocarnivores (<0.50 and <0.04 mg/kg dw, respectively).

Fig 1. The area where the animals were collected is located at the Polish-German border.

Winds in this part of Europe are mostly from south-west and organisms living in the area are exposed to emissions from both local and distant sources.

Fig 2. For several decades, this part of Europe has seen an increasing number of alien carnivores (raccoon, raccoon dog, American mink).

Together with native species, they constitute a group of mammals with diverse food preferences, which is especially reflected in Hg levels.

Fig 3. Analysis of data on raccoon, found frequently in the WMNP, shows a significant relationship between brain Hg levels and body weight in this partly piscivorous species.

Fig 4. Krey et al. [83] have recently conducted extensive analysis of the brain Hg levels in a multi-species group of mammals, indicating relationships between various Hg concentrations and neurological changes.

In our study, we used that analysis to classify the animals we studied based on brain Hg levels. Most often, the highest Hg levels, indicating neurobehavioural and/or neurochemical changes, were observed in mammals with some share of fish in their diets. These were minks, otters and raccoons, many of which were killed on roads.