By Hannah Corsini, Freelance Writer

Published October 16th, 2022

On the 5th of November 2015, the Fundão dam collapsed, unleashing a tsunami of mud which killed nineteen people and left thousands of others homeless. The event has since been referred to as the country’s ‘biggest environmental disaster.’

Originating from the Brazilian state of Minas Gerais, the mud released by the dam flowed through the Doce river into the surrounding sea, bringing mining residue contamination along with it. This coastal region is currently inhabited by a decently-sized population of 595 franciscana dolphins (Pontoporia blainvillei). However, a recent study has indicated that these dolphins may still be suffering from the after-effects of the dam collapse.

Franciscana dolphins are the most endangered dolphin species in the western South Atlantic, the part of the globe to which they are endemic. According to the National Marine Mammal Foundation, Franciscana dolphins are dying in ‘unprecedented numbers’, which has been ascribed by scientists to the fact that their coastal and estuarine habits put them in close proximity with human activity.

The population inhabiting the Brazilian coast is particularly threatened by persistent organic pollutants (POPs), which exist as a remnant of the mine collapse. POPs are organic compounds, often given the name ‘forever chemicals’ for their ability to persist in the environment and resist degradation. The compounds accumulate in the body fat of living organisms, and become more concentrated as they work their way up the food chain.

In previous years, POPs have shown to be able to affect the immune and reproductive systems of marine mammals such as dolphins. Franciscana dolphins are particularly excellent indicators of the presence of POPs, due to factors such as their high feeding frequency, their tendency to occupy the same or similar locations throughout their life, their high trophic level in food webs and their thick layer of blubber.

‘Franciscana dolphins are the most endangered dolphin species in the western South Atlantic.’

Scientists collected blubber samples from the carcasses of 33 stranded franciscana dolphins around the Espírito Santo coast, an area which receives the discharge from the Doce river. They then tested the blubber for organohalogens—a type of POP which has long-been known to cause adverse effects in both humans and wildlife. Twenty-three carcasses were tested before the dam collapse, and 10 afterwards.

Even before the dam collapse, the organohalogen compound profile in the dolphins was consistent with that of other dolphin populations that feed in highly urbanised areas, suggesting a human influence on these franciscana populations.

An organobromine flame retardant known as PBDE 47, which can serve as a potent animal neurotoxin, was found in over 50% of the dolphins. PBDE 47 presence was detected despite the fact that PBDEs are no longer produced in Brazil. The findings suggest that they have leached from discarded household goods into the marine ecosystem.

The scientists also found traces of Dichlorodiphenyltrichloroethane (DDT) within the dolphin population. DDT is an organochlorine pesticide which became commercially popular during World War II. It was later made infamous by the 1962 publication Silent Spring by Rachel Carson which decried its toxicity to wildlife.

DDT has been demonstrated to have effects on the livers, brains, fertility and immune systems of various animals, and was consequently banned in the US in 1972. In Brazil, DDT was legal until 2009, and its concentrations within the surveyed franciscana dolphins were at their peak in the years of 2005 and 2008.

For a short while after the DDT ban, its presence in the franciscana dolphins declined, along with that of other organochlorine pesticides. However, after the Fundão dam collapse, their concentrations surged once more—likely due to the subsequent physical and chemical alterations to the Doce river and the disturbance of its sediment, rather than any new deposits of DDT into the environment.

‘The scientists also found traces of DDT within the dolphin population.’

Furthermore, some of the trace metals released after the dam collapse could have reduced the soil adsorption of the organochlorine pesticides, facilitating their transport through the river. Many of the individual dolphins sampled after the dam collapse were young, but their determined concentrations of organochlorine pesticides were still worryingly high.

This is particularly concerning given that previous studies have shown that pesticide accumulation is more difficult in younger marine mammals, suggesting that these dolphins have been exposed to especially high rates of organochlorine pesticides. The only good news is that because the scientists found previous declines in these pesticides, it is likely that—barring another exceptional circumstance÷another decline will follow.

This is not the case, however, for polychlorinated biphenyls (PCBs).— PCBs are another type of POP which, like DDT, were banned in the US in the 1970s due to their impact on the health of humans and wildlife, including neurotoxic, immunotoxic, carcinogenic and endocrine effects. A similar ban against PCBs in Brazil came into force in the 1980s.

However, in both countries, and in many others around the world, PCBs still exist in the natural environment due to a legislatory failure to account for pre-existing apparatuses containing PCBs, along with their accidental manufacture as a waste by-product in industrial factories.

Previous studies of PCBs in cetaceans of the Southern Hemisphere have shown that PCBs are far more stable in the environment. Before the dam collapse, PCBs dominated the toxicological profile of the dolphins. After the collapse, scientists found far more DDTs than PCBs in the dolphin blubber, with further evidence suggesting that PCB concentrations within the population had actually declined.

The researchers ascribe this to younger populations of dolphins, along with the physical and chemical alterations made to the water, rather than actual degradation of the chemicals within the environment.

‘Even now, six years on, if you put a magnet in a plastic bag and if you touch the mud around the river, it sticks.’—Jonathan Knowles.

To summarise, the study showed that the franciscana dolphin populations in Brazilian coastal waters have experienced long-term exposure to persistent organic pollutants: both a chronic exposure to chemical groups, such as PCBs and PBDEs, and a more recent burst in exposure to DDTs as a result of the collapse of the Fundão dam.

The study reflects a legacy of environmental harm caused by both the mining industry and the dam collapse, and the necessity of remediation work in this area. This is especially important to note given the upcoming legal trial faced in the UK by the Anglo-Australian multinational mining company BHP—a £5 billion lawsuit pursued by 200,000 people affected by the disaster.

In an interview for The Guardian, Jonathan Knowles, a Yorkshireman who had been living in Minas Gerais at the time of the collapse, stated that ‘even now, six years on, if you put a magnet in a plastic bag and if you touch the mud around the river, it sticks.’

In assessing the true scale of destruction and devastation caused by the Fundão dam collapse, we can understand its gravity and take steps to ensure that something like this never happens again.

Feature Image: Sofia Khlebnikov | Unsplash

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