The killer has been found inside the crocs
Scientists have discovered high levels of banned toxic pesticides in crocodiles and fish at a World Heritage Site in SA
The discovery of high levels of DDT and other toxic pesticides in crocodiles and fish in the iSimangaliso Wetland Park in KwaZulu-Natal has raised concern about the ecological health of the country’s first World Heritage Site – and the potential risks for people who eat fish and other contaminated water creatures.
Local scientists say they have found widespread and “highly elevated” levels of DDT and other banned pesticides in Lake St Lucia, Kosi Bay, Lake Sibaya, Nsumo Pan and other wetland areas in northern KZN.Because of the widely-documented human health and environmental risks associated with this toxic chemical, DDT has been banned internationally for several years – but was re-introduced as an emergency measure in parts of South Africa just over a decade ago to control the spread of malaria along the Mozambique, Zimbabwe and Swaziland borderlines.Researchers from three local universities also found high levels of lindane, aldrin, dieldrin, heptachlor and endrin in tail fat tissue from crocodiles in a study published in the latest issue of the science journal Chemosphere.“DDT and its metabolites were the dominant compounds detected in most samples, with DDT concentrations ranging between 520 and 3100 ng g-1 ww (parts per billion) ...“Our findings show that crocodiles are exposed to organochlorine pesticides throughout their range within iSimangaliso Wetland Park and contain some of the highest concentrations ever recorded in crocodilian tissue,” said Dr Marc Humphries, an environmental geochemist and senior lecturer in the Wits School of Chemistry.The crocodile research is the latest in a series of studies that have highlighted the extent of DDT and other pesticide pollution in fish, crocodiles and mud samples, as well as flagging the potential danger to human health in the region through the continued use of DDT to control malaria.
A separate study for the Water Research Commission in 2016 also found high levels of DDT in all fish species tested in the Lower Phongolo River and floodplain, downstream of the Jozini Dam.Because local people harvest fish on a subsistence basis, the commission research team warned that the DDT levels they found “pose a potential serious health risk to the local community”.
“Based on these findings it is imperative that the continued use of DDT in this area should be re-assessed as well as the current health status of the people of this region should be investigated.”These concerns are echoed in the more recent studies by Humphries and fellow researchers from the universities of Witwatersrand and Pretoria and Tshwane University of Technology.“Many of the samples analysed exceeded European Commission maximum residue limits with potential dietary risk associated with exposure to heptachlor, heptachlor epoxide and dieldrin. While these results highlight the potential health risks associated with the consumption of contaminated fish sourced from iSimangaliso, the exposure of local people to organochlorine residues could be considerably higher and warrants further investigation.”
From an ecological perspective, Lake St Lucia is home to the largest Nile crocodile population within a single waterbody in SA and is seen as one of few remaining viable breeding populations in the country for these apex predators.Humphries said DDT and other toxic and persistent pesticides had been used extensively around the world as farm insecticides and to combat insect diseases and their use in Maputaland became prevalent in the early 1950s.
“Arguably the most well-known of these is DDT, which has been used to combat the spread of malaria in the region. However, the use of such chemicals presents numerous human health and ecotoxicological issues.”DDT
Dichlorodiphenyltrichloroethane (DDT) is a colourless, tasteless and almost odorless organochlorine, developed as an insecticide first synthesised in 1874. DDT was used in the second half of World War 2 to control malaria and typhus among civilians and troops.He said organochlorine compounds are highly toxic to aquatic life and can persist in the environment for several decades. Although these compounds degrade over time, their breakdown products are often toxic and even more persistent in the environment.
“Today the use of these chemicals has been phased out and completely banned in most countries. South Africa continues to employ certain compounds on a limited basis and the Department of Health regularly uses DDT in northern KZN because of its effectiveness in reducing malaria infections. However, this remains a controversial issue because of the associated environmental and human health risks,” he cautioned.Asked whether the national Health Department was re-assessing the use of DDT for malaria control and whether it had initiated research to determine health risks to local communities, department spokesperson Popo Maja referred queries to the KZN Health Department.
Spokesperson for the KZN department of health, Ncumis Mafunda, said: “The department is aware of the findings and recommendations of the two studies. The department is not considering re-assessing the DDT use via Indoor Residual House Spraying in northern KZN because it is done on the inside walls of the homesteads and not on any water sources.”
Last November the national department said South Africa was working with Mozambique and Swaziland to eliminate malaria transmission by 2020.“South Africa has made huge strides in reducing malaria morbidity and mortality over the past decade. Malaria cases have decreased by 91%, from 64,622 cases in the year 2000 compared to 5,777 cases in the year 2016, and malaria deaths have also decreased by 89%, from 406 to 42 deaths between 2000 and 2016.
“However, in 2017 malaria cases in South Africa and rest of the Southern African region have increased due to several factors, which were exacerbated by favourable climatic conditions for transmission.
“The Department of Health is ensuring universal coverage of key interventions such as: indoor residual spraying, effective case management and ensuring that health promotion messaging reach communities at risk of contracting the disease.”DDT is one of several persistent organic chemicals whose global use had been banned under the Stockholm Convention, with some exceptions for emergency use. These chemicals are absorbed in fatty issue, where concentrations can become magnified by up to 70,000 times the background levels. Fish, predatory birds, mammals and humans are high up the food chain and so absorb the greatest concentrations.
A recent scientific review in The Lancet says DDT at amounts that would be needed in malaria control can cause premature births in people and possible disruption in semen quality, menstruation and pregnancy.