Fatty acids as bioindicators of organohalogen exposure in marine fish from a highly polluted estuary: First insight into small-scale regional differences

Fatty Acid Profiles Linked to Organohalogen Exposure in Cetaceans from the Northern South China Sea

Increasing evidence suggests that organohalogen contaminants (OHCs) could disrupt lipid metabolism in organisms, prompting consideration of fatty acids (FAs) as biological tools for assessing chemical stress in biological systems. This study examined 87 OHCs and 32 FAs in two sentinel cetacean species─Indo-Pacific humpback dolphins (n = 128) and Indo-Pacific finless porpoises (n = 26)─from the northern South China Sea (NSCS), a global hotspot for OHCs. Our results revealed higher OHC levels in these cetaceans than global averages. We identified 347 significant correlations between 79 OHCs and 32 FAs, including 32 associations with long-chain n-3 polyunsaturated fatty acids, which are critical for cetacean health. Furthermore, 45 significant correlations were found between OHC levels and desaturated enzyme activities/lipogenic indexes, suggesting that OHCs may disrupt lipid metabolism in these cetaceans. Polybrominated diphenyl ethers as legacy flame retardants were major contributors to the OHC-FA relationships. Moreover, alternative halogenated flame retardants, as PBDE substitutes, may similarly impact FA metabolism, raising concerns regarding their safety. Our findings support the potential use of FAs as bioindicators for evaluating OHC exposure risks in cetaceans. Future research is needed to elucidate the mechanisms and consequences of these OHC exposure-associated lipid-disrupting effects occurring in the NSCS cetaceans.

Organohalogen contaminants threaten the survival of indo-pacific humpback dolphin calves in their largest habitat

As long-lived apex predators, marine mammal adults often accumulate alarmingly levels of environmental contaminants. Nevertheless, the accumulation and risks of these contaminants in the critical calf stage of marine mammals remain largely unknown. Here, we investigated the exposure status and health risks of 74 organohalogen contaminants (OHCs) in Indo-Pacific humpback dolphin calves (Sousa chinensis) collected from the Pearl River Estuary (PRE), China, during 2005-2019. Our findings revealed moderate levels of polychlorinated biphenyls (PCBs), medium-high levels of dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs), and the highest levels of polybrominated diphenyl ethers (PBDEs) and alternative halogenated flame retardants (AHFRs) compared to those reported for cetaceans elsewhere. Traditional OHCs like DDTs, PCBs, and PBDEs did not exhibit significant decreasing trends in the dolphin calves despite global restrictions on these compounds, and AHFRs as emerging OHCs showed an increasing trend over the study period. Risk quotients of DDTs, HCHs, PBDEs, and PCBs in most of the dolphin samples were > 1, indicating that humpback dolphin calves may have suffered long-term threats from OHC exposure. The significant correlation observed between the traditional OHC levels and the stranding death number of the dolphin calves suggests these OHCs may impact the survival of this endangered species.

Organotins in fish, shrimp, and cephalopods from the Pearl River Estuary, China: Dietary exposure risk to Indo-Pacific humpback dolphin and human

Food has regularly been proven to be a key source of exposure to environmental pollutants, drawing attention to the dietary exposure risks of contaminants to mammals with significant daily food intake. Here, the levels of six organotin compounds (OTs) in 18 fish (n = 310), three cephalopods (n = 50), and one shrimp (n = 34) from the Lingdingyang (LDY) and west four region (WFR) of the Pearl River Estuary (PRE) and their dietary exposure risks to Indo-Pacific humpback dolphins and humans were first investigated. Total OT levels ranged from 3.84 to 901. 48 ng/g wet weight (ww) in 22 prey species from the LDY, and from 14.37 to 1364.64 ng/g ww in 19 species from the WFR. The LDY marine species generally accumulated higher butyltin levels but lower phentyltin levels than those in the WFR. All species have a phenyltin degradation index <1 and over 60 % of the sampled species have a butyltin degradation index <1, suggesting the PRE marine species might be exposed to the fresh discharge of OTs. A total of nine marine species exceeded the threshold levels of OT intake for adverse health effects on human juveniles by consumption, all 22 marine species posed high dietary risks to the PRE humpback dolphins. Moreover, probabilistic risk assessment using Monte Carlo simulation revealed that the probabilities of RQ values associated with WFR OT exposure higher than 1 were 18.87 % for human adults, 40.55 % for human juveniles, 100 % for both humpback dolphin adults and humpback dolphin juveniles. Our results highlighted the potentially high dietary exposure risks of OTs to marine mammals and residents in the PRE.