Exposure to organic contaminants and effects on oxidative stress endpoints in top predatory birds of Pakistan

Abstract

Organic contaminants are often persistent, bioaccumulative, toxic chemicals which can travel large distances in the environment. Release of these ubiquitous contaminants through rapidly increasing, industrial, urban and agricultural sources pose a major threat of contamination to human and wildlife health. Predatory birds, being at the top of the food chain, are therefore especially vulnerable to such contamination. To date, very little is known about the organic contaminants exposure and its effects on top predatory birds of South Asia, in particular those of Pakistan. In addition, knowledge on organic contaminants mediated oxidative stress response in free ranging predatory birds is rather limited. In this doctoral thesis, concentrations of various legacy compounds such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs), Hexabromocyclododecane (HBCDDs) as well as emerging 1,2-bis (2,4,6-tribromophenoxy) ethane (BTBPE), bis (2-ethylhexyl)-2,3,4,5-tetrabromophthalate (BEH-TEBP) and 2-ethylhexyl-2,3,4,5-tetrabromo-benzoate (EH-TBB) were analyzed in ten species of free ranging top predatory birds from Pakistan. Several variables such as dietary habits (quantified using stable carbon and nitrogen isotopes), taxonomic and trophic level, habitat and feeding regimes of the species were investigated for their contribution to intra and interspecific variations. Special focus was paid on using their feathers, and therefore different feather types were evaluated for their suitability in black kite (Milvus migrans). Further, paired feathers and blood samples were used for black kite and spotted owlet (Athene brama) to investigate whether feather reflect internal body burden of organic contaminants. Moreover, effect of the organic contaminants exposure on oxidative stress, i.e. the activity of antioxidant enzymes such as glutathione peroxidase (GPx), glutathione S-transferase (GST), glutathione reductase (GR) and catalase (CAT), or expression of GPx and superoxide dismutase (SOD) genes was investigated in these latter two species as well. Among PCBs and OCPs, highest concentration in tail feathers were recorded for isomer dichlorodiphenyldichloroethylene (p,p´-DDE) followed by dichlorodiphenyltrichloroethane (p,p´-DDT), hexachlorobenzene (HCB), ∑PCBs and trans-nonachlor (TN) respectively. In comparison, BFRs concentrations in tail feathers generally followed the trend as ∑PBDEs>∑HBCDDs>BTBPE. Other emerging BFRs such as BEH-TEBP and EH-TBB were not detected in any sample. In tail feathers, CB 118, 153, 138, and 180 along with p,p´-DDE were most frequently detected compounds among PCBs and OCPs. Hexa- and hepta-CBs were more prevalent in terrestrial while penta-CBs were dominating in aquatic species. Similarly, BDE-47 was most prevalent BFR compound in aquatic species, BDE-99 and -153 were so in terrestrial species and α-HBCD was in general found as predominant BFR in tail feathers. The concentrations of ∑PCBs, ∑DDTs and TN differed significantly among feather tIn general, concentrations of organic contaminants were highest for body feather followed by tail, secondaries and primaries respectively. Body feathers were evaluated as best potential bioindicator based on higher detection frequency of organic contaminants, however feather selection could vary depending upon the goals of the study. Variables such as species, trophic level and origin of dietary carbon (δ13C) were evaluated as major factors explaining intra and interspecific variations. These factors along with other biological and ecological variables may synergistically influence the bioaccumulation of organic contaminants in predatory birds. In general, regressions between feathers and blood organic contaminants concentrations were non-significant which reflect that feathers are not always suitable indicator for internal blood levels, depending on the type of the feathers and the age of the bird. Regression analysis revealed that the activity of GST and GR was significantly associated with the level of p,p’-DDE in blood from the spotted owlet. Similarly, activity of CAT and GR was significantly correlated with BDE-100 concentrations in tail feather from the spotted owlet. In comparison, mRNA expression of SOD was found significantly associated with ∑PBDEs level in blood from the spotted owlet as well as with p,p’-DDE levels in feathers from the black kite. It is deduced that oxidative stress endpoints are positively correlated with exposure to organic contaminants, threshold for which can be tested through cause-effect based studies in future. This is the first ever report where oxidative stress endpoints are associated with feathers concentrations of organic contaminants. Current exposure assessment scenario indicated that concentration of various organic contaminants are rising in predatory bird species of Pakistan. Exposure to high concentrations of organic contaminants may cause serious health effects in populations of predatory birds of Pakistan. Exposure to organic contaminants as well as contributing factors to intra and interspecific variation should be further elucidated in future studies. Further, cause-effect based investigations are necessary to corroborate the potential of various organic contaminants in inducing oxidative stress response in top predatory birds. Formulation of proper policy and regulations, and their strict implementation are immediately needed to protect the already declining predatory bird species of Pakistan, particularly from toxic effects of organic contaminants. ypes in black kite.