The distribution and stratification of persistant organic pollutants in the blubber of bottlenose dolphin (Tursiops truncatus)

Marine mammal blubber, such as that of the bottlenose dolphin ( Tursiops truncatus), has been used to estimate environmental organic contaminant concentrations for decades. However, little is known about the distribution of these compounds as a function of blubber depth and across the body of the animal. With the inherent variability in blubber sampling techniques currently used, such as dart biopsies which may not fully penetrate the blubber layer and may strike different body locations, it is important to understand if blubber stratification or body location affects persistent organic pollutant (POP) concentration. To investigate these effects on POP concentrations, six full depth blubber samples were taken from one dolphin to assess variation in fatty acid distribution and contaminant storage with body location. Three of the blubber samples were separated into distinct layers based on histological examination to determine if organic contaminant stratification in the blubber was similar across body locations. In this one individual, both organic contaminant and fatty acid distributions were heterogeneous with blubber depth and body location. POP concentrations were significantly greater in ventral and anterior body locations and greater in the outer layer when compared to the inner layer. In addition, a greater proportion of dietary fatty acids were found in the dorsal blubber and in middle and inner layers relative to other locations while a greater proportion of biosynthesized fatty acids were found in the ventral blubber and outer layers. These results suggest that organic contaminant data obtained from partial depth samples or from a sample site other than the intended biopsy site should be interpreted with care. Full depth blubber sampled from the same location on seven individual bottlenose dolphins was also separated into layers and analyzed for POPs and fatty acids. Lipid normalized contaminant concentrations were not significantly different among blubber depths. These results suggest that although contaminant concentrations vary within an individual as a function of blubber depth, partial depth dart biopsies may be used to assess the health of bottlenose dolphins when larger sets of samples are used and when the samples come from a similar location.