Current Status and Future Prognosis of Malaria Vector Control Pesticide Ecotoxicology and Xenopus sp.

Abstract

Whilst frogs are generally considered as good indicators of environmental change, they are not widely utilised as indicators in ecological studies. With much of current research relying on model organisms as proxies for other animals or even humans, toxicology data on these model organisms is important for higher tier risk assessment studies and ecological modelling. The issue at hand is that for some topics, even when looking at model organisms, this empirical data does not seem to be as common as expected when doing literature research. Malaria vector control (MVC) is often a sensitive subject due to the paradox surrounding it (Bouwman et al. 2011). The lack of toxicological data mentioned feeds into the issues complicating debates on the chemical vector control interventions. Although being in use for decades, there are still many unknowns regarding the environmental impact of these pesticides. Informed decision making and policies require that this information first be available. The main research problem investigated in this review is this lack of toxicological and biomonitoring data available for one of the model organisms (Xenopus laevis) representative of aquatic ecosystems, and to a lesser extent, anurans. Species from the Xenopus genus are endemic to Africa and their distribution includes many areas where malaria vector control is applied. Reliable toxicology data on these frogs regarding malaria vector control pesticides (MVCPs) would strengthen the use of these animals as bioindicators.

Sub-lethal exposure to malaria vector control pesticides causes alterations in liver metabolomics and behaviour of the African clawed frog (Xenopus laevis)

“…The validation results of the extraction and analysis methods for DTM used in this study indicated that the method was effective for the extraction and analysis of DTM. No published literature is available on the accumulation of DTM in Xenopus tissue (see Wolmarans et al 2020). Studies on fish such as Szegletes et al (1995) also failed to measure DTM residues in tissue samples.…”

“…The two pesticides tested, DDT and DTM, were selected in this study as representatives of IRS pesticides. The scope of this study and ethical limitations on the use of vertebrate animals did not allow for extensive LC50 testing on adult frogs, and no literature containing LC50 data on adult X. laevis was found in a recent review (see Wolmarans et al 2020). Therefore, the LC50FETAX values (DDT= 35.7 mg/L and DTM = 0.19 mg/L, Channing 1998;Saka 2004) based on toxicity to larval X. laevis were used as a starting point for lethality, even though sensitivity between adult and developmental stages of animals can differ.…”

“…There is a distinct lack of sub-lethal toxicity literature related to anurans and MVC pesticides, particularly in African species (Wolmarans et al 2020). In this study, with the above mentioned integration framework in mind, we combined chemical accumulation, metabolomics, and behaviour as toxicological endpoints to explore the integrated effects of these pesticides on the fully aquatic anuran Xenopus laevis in a laboratory setting.…”

Registro e perfil ecotoxicológico de produtos para controle de Aedes aegypti

“…Contudo, o potencial de acumulação de outros pesticidas em sapos é desconhecido. Detectou-se que malationa e alguns piretroides apresentaram toxicidade para este modelo 15 . Um estudo considerou metopreno e Bti como inseticidas de baixo risco para organismos não alvo com base nas concentrações detectadas no ambiente 63 .…”

“…Organoclorados, como o dicloro-difenil-tricloroetano (DDT), apesar de terem sido banidos em muitos países, são os pesticidas encontrados em maior concentração no solo e na água em virtude de sua lenta biodegradabilidade 13,14 . Outro prejuízo ambiental referente ao uso de inseticidas está relacionado aos efeitos em organismos não alvo, como animais aquáticos, répteis, anfíbios, plantas e polinizadores 15 . Não só os inseticidas ambientais, mas aqueles aplicados na pele apresentam risco ao meio ambiente 16 .…”