Tadpoles & Cocktails: Detecting the chemical threat

I’d just hammered down the first tent peg when the wind hit us. It wrenched the rope from my assistant’s hand. The tent toppled over and started cartwheeling down the slope towards the pan.

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I‘d just hammered down the first tent peg when the wind hit us. It wrenched the rope from my assistant’s hand. The tent toppled over and started cartwheeling down the slope towards the pan. He ran after it into the water, but both his heavy gumboots got stuck in the grass. crashed down in the shallow water and mud like a log. A lightning bolt struck the gum trees behind us and big raindrops started to come pouring down. The tent didn’t stop when it reached the water’s edge, but like a sailing ship was driven by the wind right across the pan.

It was one of those old tents where you first bolted the frame together and then pulled the canvas over, but at the time it was new. It was the first time I’d used it. Soaking wet, we had to get into the bakkie and drive right around the pan to retrieve our tent, dismantle it and bring it back, because without it we had no protection. The pan was large, over a kilometre across, but very shallow and filled with grass, which prevented the tent from sinking. It was one of the many large pans around Benoni, where did my research on bullfrogs 40 years ago. It was the perfect habitat for the multitude of giant bullfrogs breeding there. They bred only in very shallow water and after every good downpour hundreds of huge, green and yellow males invaded the pan to engage in battle with each other. day or two later the females arrived to each lay several hundred eggs. In less than 20 days the little frogs would emerge from the pan to swarm in countless numbers in all directions. It attracted swarms of birds that preyed on them and was an incredible sight.

The frequent rainstorms, however, made round-the-clock fieldwork very difficult, so decided to do some observations in a concrete dam at home. added some soil to the 10cm of rainwater in the dam to create a slope. It worked fine and the frogs bred well. But then the rain stopped and it became very hot. The water started to evaporate. To prevent it from dropping too low, added some municipal tap water. Within an hour all the tadpoles were dead.

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A warning from the frogs
The tadpoles of most frogs are extremely sensitive to chemicals in the water and are supreme indicators of the health of the environment. However, hordes of tadpoles nowadays develop into misshapen and sterile frogs and there is widespread consensus that frogs and other amphibians are globally experiencing widespread extinction. Apart from direct death from poison in the environment, frogs and tadpoles die on a massive scale from fungal and bacterial infections, which have until now been blamed on global warming, which creates conditions favourable for infections. However, 10 prominent American scientists recently published a report which tells a completely different story, which should concern every field sportsperson. The scientists exposed leopard frog tadpoles to the nine most common herbicides, insecticides and fungicides used on agricultural fields in Nebraska. Each chemical was applied separately at doses the manufacturers described as “sub-lethal” – 4% of the tadpoles died. Next they exposed the tadpoles to a mixture of all nine chemicals, as they would experience in real life, but at only 1/10 000th of the previous dose and guess what?

All the tadpoles died!
The big surprise was that they didn’t die from the poison-cocktail, but from infections by bacteria they’d always carried naturally. This report for the first time demonstrated that environmentally-relevant exposures to mixtures of pesticides undermine the immune systems of developing leopard frogs. makes them extremely vulnerable to bacterial infections they otherwise would have resisted, rendering them even more defenceless against secondary fungal attack. It was initially suggested that it was a new fungus that had spread into new areas, but in fact what has been spreading is the frogs’ inability to fight an infectious agent already present.

This is very disturbing, as it makes all so-called “safe” levels of pesticides totally meaningless. Chemical pesticides are always tested in isolation, which is never how we encounter them in the environment. Animals and people are never exposed to only one pesticide at a time, but to hundreds of them simultaneously. We can’t avoid it. All the food we eat and all the liquids we drink contain residue of pesticides. Not only because we spray it on almost all agricultural products, but because it is in the soil, the air and even the rain. Some are stored in the fatty tissues of our bodies and are mixed into deadly cocktails in our blood. The fact that the synergistic action of a multitude of pesticides that come together can have such a devastating effect on our immune systems perhaps explains many things we did not understand in the past.

In the old days there was perhaps one doctor in town, who made a reasonable living. Today there are hundreds in every city and the medical profession has become one of the most lucrative. The waiting areas of every hospital, clinic or consulting room are overflowing with sick people and with every consultation the money rolls in. Cancer, a rare disease in the old days, has become one of the biggest slayers of mankind.

Denying the danger
The research on frogs also explains why it’s so difficult to prove the cause of illness brought about by chemical-induced immune deficiency. That’s why the chemical industry can so aggressively reject any allegation that their products are to blame. This is exactly what happened the other day in Groblersdal, where a local doctor became concerned when many of his patients turned up sick, displaying symptoms he recognised as signs of cholinesterase inhibition. Living in the same environment as his patients, he began to experience the same symptoms and started regularly testing cholinesterase levels in his own and his family’s blood. Cholinesterase is one of the most important enzymes needed for the proper functioning of the nervous systems of humans, other vertebrates, and insects. Certain pesticides like organophosphates and carbamates inhibit or neutralise its effect, disrupting the proper functioning of the nervous system. In insects and small animals like birds this causes death, and in humans it usually suppresses the immune system and causes chronic illnesses.

Human exposure can result during and after aerial spraying of these pesticides, from inhalation, ingestion, and eye or skin contact. The doctor found that in spraying season the levels of the cholinesterase enzyme in the family’s blood dropped significantly. When he made his findings known, he was pounced upon by the chemical industry, the media, his own colleagues and the farming community. A spokesperson from the Association of Veterinary and Chemical Associations of South Africa (AVCASA) issued the usual press statement that no scientific proof exists and that regular tests have shown pesticide residues are within safe levels.

But the tests were done for single pesticides and the frogs have shown we don’t know what safe levels are, because we’re always exposed to a multitude of chemicals. The danger can even be greater than the doctor suspected. The effect of long-term exposure is also unknown. We can’t condone situations like these. None of us want to live with chronic ill health or the possibility of cancer. This situation exists in many places and touches every consumer. Farmers are not only obliged to feed the nation, but to see to it that as little pesticide residue as possible remains in their produce.

The impact of pesticides on the environment is enormous and largely still poorly understood. The catastrophic death of a now suspected estimate of about 500 crocodiles in the Kruger Park is an example and scientists are still unsure of the cause. It’s thought they ate too much rotting fish, when just about all the tigerfish in the Olifants River gorge died. I’m not convinced, but what concerns me most is that nobody knows what killed the tigerfish – if they are the canaries in the cage that warn us, we may not even know what they’re warning us against. – Abré J Steyn
Contact Abré J Steyn on
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Photos: Abré J Steyn