Legacy organic pollutants are still a threat for resident dolphins of south-east Australia

This study investigates the concentrations of persistent organic pollutants (POPs), specifically polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane (DDT) and its derivatives, in the blubber of three dolphin species stranded along the Victorian coast (Australia) from 2002 to 2022: Burrunan dolphins (Tursiops australis, n=19), common bottlenose dolphins (T. truncatus, n=6), and short-beaked common dolphins (Delphinus delphis, n=7). ΣDDT concentrations generally exceeded Σ₉PCBs across most individuals, with Gippsland Lakes (GL) Burrunan dolphins showing the highest ΣDDT concentrations (1400 to 598,000 ng/g lw), including a maximum of 598,000 ng/g lw in one individual-comparable to dolphins in heavily contaminated areas globally. DDE was the most dominant congener, reflecting its persistence. The DDE/ΣDDT ratio (0.46-1) indicates a historical DDT source, with possible remobilization from land-based stores. PCBs were primarily hexachlorinated congeners (PCB-138, PCB-153, and PCB-156), with extreme Σ₉PCB levels found (up to 837,000 ng/g lw). Port Phillip Bay Burrunan dolphins and common bottlenose dolphins showed a decline in PCB levels over time, while GL Burrunan and short-beaked common dolphins exhibited minimal change. The widespread presence of hexachlorinated congeners suggests ongoing local PCB contamination despite the 1975 ban on PCB imports. This first multi-species POP assessment in the region reveals PCB and DDT levels that exceed health thresholds in 23 of 36 individuals, impacting 89% of critically endangered Burrunan dolphins. Despite limitations of stranded specimens, this study highlights significant, ongoing risks from banned PCBs and DDTs, underscoring the need for continued monitoring.