A new international study involving Nelson Mandela University (NMU) has pointed to worrying levels of chemical toxins in dolphins in South African waters, most likely as a result of feeding on contaminated fish.
The Spain-SA study reveals double the safe level of organophosphates – chemical compounds from fertilisers, pesticides and microplastics – in the muscle tissue of dissected humpback, bottlenose and common dolphins.
The study also discovered plasticisers, which are used in a wide variety of products including plastics and concrete, and flame retardants, used in the motor vehicle, computer and television manufacturing industries.
Dr Stephanie Plön, a marine mammal specialist from NMU, said on Wednesday the dolphins that were dissected had been caught in the shark nets off Durban, and marine chemical pollution was likely lower off the Eastern Cape coast.
But the study pointed to a worrying global trend.
“I’m finding increasing evidence of a deterioration in the health of marine mammals and this raised level of chemical poisoning is a central part of the picture,” she said.
“Combined with depleted food resources due to overfishing and climate change, as well as the ingestion of plastic debris and rising stress levels from shipping and marine construction noise, it was not surprising that dissections of whales and dolphins were revealing more and more ulcers and diseases.
“But while all these other factors are important, I feel like chemical pollution has been going unnoticed until now, and this is the value of these international studies.”
The study, led by the Spanish National Research Council, noted the previous finding that ingested organophosphates could damage the nervous, hormonal and reproductive systems of animals.
The dominant organophosphate in the latest study was tributoxyethyl phosphate at levels of up to 32 micrograms per gram of body weight.
Earlier studies on rats had set the no-observed-adverse-effect maximum at 15 micrograms, according to council researcher Ethel Eljarrat.
“The levels we have found in the dolphins analysed should not be underestimated, and it is necessary to avoid the increase of these levels of toxic compounds, which can jeopardise the health of the marine animals,” she said.
The study found that the level of organophosphate poisoning in the sampled South African dolphins was 10 times higher than that which had been found in an earlier study in dolphins from the Alboran Sea – a body of water in the far southwest of the Mediterranean, sandwiched between Spain, Gibraltar and Morocco.
Plön said contributing factors for this finding could be the many rivers flowing into the sea along the KwaZulu-Natal coast combining to deliver a heavy pollution load.
She referred to a 2016 study published by her and colleagues which pointed to high levels of chemical pollutants, possibly from fertilisers and pesticides, off KwaZulu-Natal.
She said while SA boasted some of the best environmental legislation, enforcement was often poor.
Among other reasons for concern were that dolphins and whales had similar physiology to humans and were also high up on the food chain.
“They’re also mammals and they eat fish. What is harmful to them will be harmful to us.”
Plön said besides collaborating on international studies she continued to work with Bayworld, dissecting dolphin and whale carcasses from strandings and fishing bycatches.
“We need to understand and quantify what is clearly a serious problem and there is great value in both these levels of research,” she said.