Linking organochlorine exposure to biomarker response patterns in Anurans: a case study of Müller’s clawed frog (Xenopus muelleri) from a tropical malaria vector control region

Abstract

Organochlorine pesticides are highly persistent in aquatic ecosystems. Amphibians, specifically anurans, play an intricate part in the aquatic food web, and have very permeable skin which makes them prone to bioaccumulation of persistent pollutants. In this study the bioaccumulation of various legacy organochlorine pesticides (OCPs)-including dichlorodiphenyltrichloroethane (DDT), currently used for malaria vector control (MVC)-was assessed along with a set of biomarker responses in Müller's clawed frog Xenopus muelleri collected from the lower Phongolo River floodplain in South Africa. Possible relationships between bioaccumulation and biomarkers (of exposure, oxidative stress biomarkers, and cellular energy allocation) alongside their temporal changes were investigated. The OCP concentrations showed a significant increase over time for the duration of the study. The increase correlated negatively with rainfall from the region. DDT levels were well below expected effects levels with p,p-DDE being the main contributing metabolite. The results of this study indicate OCPs actively accumulate at sub-lethal levels in aquatic frogs from the study area, while showing possible relations towards some of the biochemical stress responses measured. Most notable were negative relationships indicated between p,p-DDE and acetylcholinesterase, malondialdehyde, and carbohydrates and protein energy availability. Levels of DDT were not found to be significantly higher than other legacy pesticides in the frog tissue, although evidence of newly introduced DDT in the frog tissue was found. Further investigation about sub-lethal effects of these pesticides on anurans is required to gain better insight into their full impact on animal livelihood.

Agrochemicals disrupt multiple endocrine axes in amphibians

“…For example, a decrease in the total lipid content of liver, muscle, testes, and ovaries were observed in Minervarya andamanensis (Andaman frog) with lethal concentration of malathion, whereas exposure to sub-lethal concentrations were associated to an increase in total lipids, free fatty acids, glycerol, and lipase activity (Gurushankara et al, 2007). A negative relationship between p,p-DDE exposure and protein and carbohydrate storage associated with increased energy consumed has been shown in Xenopus muelleri (Müller's clawed frog) (Wolmarans et al, 2018). L. sphenocephala exposed to single, double, or triple pesticide mixtures of bifenthrin (insecticide), metolachlor (herbicide) and triadimefon (fungicide) presented an increase in amino acids and other key metabolites concentrations in liver, suggesting depletion of energy resources (Glinski et al, 2018).…”

Regional Scale Risk to the Ecological Sustainability and Ecosystem Services of an African Floodplain System

“…This foundation research has contributed to the understanding of the dynamics of ecosystem functioning and the impacts of the dam and associated altered flood and flow releases on the integrity of the system Merron et al., 1993 Then in the 1990s and 2000s a shift in research occurred toward the social and ecological interactions, with a new emphasis on the characterization of ecosystems services, local community requirements, threat of pollutants to the health of communities, and the management of conflicts between regulators and local resource users (Bouwman et al., 1990; Breen et al., 1998; Heeg & Breen, 1994; Jaganyi et al., 2008; McCartney et al., 2003; Thompson et al., 2017; Yohannes et al., 2017). In the 2000s and 2010s many gaps in our understanding of specific biology, ecology, ecotoxicology, and socioecological issues were addressed (Bouwman et al., 2019; Coetzee et al., 2015; Dube et al., 2017; Evans & Bouwman, 2000; Nkhata, Breen, Hay, & Wilkinson, 2017; Volschenk et al., 2019; Wepener et al., 2012; Wolmarans et al., 2018). This research has culminated with ecosystem service and poverty alleviation plan development (Lankford et al., 2011) the implementation of South African water resource management measures to establish the Ecological Reserve and associated Environmental Flow requirements for the Phongolo Floodplain (Brown et al., 2018; Dube et al., 2015; DWS, 2014).…”

Emerging concepts and opportunities for endocrine disruptor screening of the non-EATS modalities

“…The exposed animals produce progeny that metamorphose later, are smaller and lighter at metamorphosis, and have reduced reproductive success ( Regnault et al, 2018 ; Usal et al, 2019 ) in addition to displaying metabolic impairments at the adult stage ( Usal et al, 2021 ). In addition, disruption of lipid, carbohydrate and protein metabolism following insecticide or pesticide mixture exposure has also been reported in amphibians ( Glinski et al, 2018 ; Gurushankara et al, 2007 ; Wolmarans et al, 2018 ).…”