The Characteristics Of Persistent Organic Pollutants Of Four Shark Species In The Eastern Pacific Ocean

Persistent organic pollutants(POPs)are chemical substances that persist in the environment,bioaccumulate through the food web,and pose a risk of causing adverse effects to human health and ecosystems.POPs can be globally transported through vast circle and bioaccumulated in human bodies or animal tissues through food chains.Sharks are top predators of marine ecosystem and play keystone roles in regulating ecosystem structure and functioning.Recent years,the global abundance of sharks have declined significantly.High contents of POPs,generally accumulated in sharks which mainly occupy the highest and median trophic position of the marine food web,are placing them at special risk from anthropogenic pollution.In this study,the research progress and applications of POPs in sharks were reviewed with the aim of evaluating their impacts on shark populations and their potential values in scientific research on shark ecology.Due to the characteristics of biomagnification,POPs concentrations are affected by multiple environmental factors,maternal offloading and the metabolic capacity of organisms.POPs in sharks are mainly concentrated in the livers because of the large quantity of fat,comprising predominantly of PCBs,DDTs,which have the potential impacts on the entire populations and communities through the effects of metabolic health,reproductive functions,immunity,and nervous system.In addition,POPs in sharks also have potential applications on clarifying allocation patterns of interspecific and intraspecific resources,trophic niche partitioning and environmental pollution assessment.Elaborate on:(1)DDTs and PCBs were generally detected in the muscle and liver tissues of four species of sharks in the Eastern Pacific Ocean,indicating that DDTs and PCBs had been generally contaminated in the fish Eastern Pacific Ocean,and the residual levels were relatively high.Compared with other studies,the residual levels of target contaminants in the four Eastern Pacific shark species were moderate.The composition characteristics of the compounds indicated that the agricultural pollution was mainly historical residues,and the main degradation mode in the environment was aerobic degradation.The high ∑PCBs/∑DDTs ratios confirm this trend,indicating the predominance of industrial contamination profile over that of agricultural origin.From a toxicological persperctive,the TEQ levels does not present a toxic risk to them.(2)The investigate levels and composition profiles of DDTs and PCBs showed significant differences in the same species different tissues.Some of these pollutants can accumulate in exposed organisms due to long half-lives and high lipophilicity,which makes it easy to be enriched in tissues with high fat content.indicating that the distribution process of DDTs and PCBs in shark tissues could be mainly a passive diffusion process affected by lipid content.Significantly higher levels of contaminants were observed in tissues with high lipid content such as liver than in tissues or organs with low lipid content such as muscle.Compared with muscle tissue,the removal rate of foreign pollutants and assimilation rate of monomer in liver tissue were faster,the biological amplification factor was higher and the half-life was shorter.The relative PCB congener composition shifted from a higher percentage of lower chlorinated congeners to a higher percentage of heavily chlorinated congeners from muscle to liver.(3)DDTs and PCBs or their metabolites have a strong persistence in ecosystems,and they are well documented to biomagnify in food webs and to be toxic for organisms.In this study,through stable isotope ratio analysis guided of carbon and nitrogen,demonstrate the applicability of organic contaminants as a tool to examine the degree of niche partitioning.Biomagnification profiles of POPs including PCBs and DDTs through aquatic food webs,and were reported to increase with trophic level.Since contaminants are acquired through diet,factors that influence feeding are hypothesized to play an important role in accumulation,and thus niche discrimination.Thus,contaminants as ecological markers may serve as a useful tool to provide insight into differential resource usage and physiology within species as well as among them.