ENVIRONMENT-URUGUAY: Eat Fish, but Skip the Liver

By Diana Cariboni Reprint | | Print |

Diana Cariboni

MONTEVIDEO, Jun 10 2004 (IPS) - In Uruguay’s coastal waters, where the Río de la Plata (River Plate) flows into the Atlantic Ocean, "lead and chrome are the heavy metals with highest concentration in the sediment," Federico Viana, a biologist with the University of the Republic, told IPS.

"Chrome is highly toxic. Even at low concentrations it has lethal effects," said Viana, head of an investigation of heavy metal contamination in fish species along the Montevideo coastline.

And there are some metals that do not kill, "but affect reproductive rates, for example, with consequences for the structure of species populations and the aquatic ecosystem," he added.

Viana proposed studying the concentration of metals – copper, zinc and mercury – in several coastal fish species, many of which are caught by Uruguayan fishing enthusiasts and small fishing operations, and end up on local dinner tables.

The scientists studied metal content in muscle tissue and in the livers of species such as the corvina, ‘pescadilla de calada’ (striped weakfish), ‘lisa’ (striped mullet), ‘pejerrey’, ‘brótola’ (codling) and catfish species.

Viana found concentrations below the suggested maximum limits in the muscles, or meat, of the seven species. But in the livers of the lisa and brótola – "the cleansing organ par excellence" – he found a greater accumulation of copper and zinc.

Another discovery emerged when the experts took into account the size of the fish. "We found signs of bioaccumulation, that is, an increase in concentrations of metals the older the fish," explained Viana.

"Considering these results, it is possible to eat our fish without running risks associated with heavy metal concentrations," he said.

"However, it is recommended to avoid larger fish," because they manifest a greater presence of heavy metals. It is also recommended that people avoid consuming the livers of these species, he stressed.

Although consumption of fish organs is not a common practice, "there are people who eat brótola and corvina organs, which exposes them to levels of contamination that could be harmful to their health," said Viana.

To establish the "acceptable limits", which are usually adopted as national health standards, Viana had to turn to the Brazilian Health Ministry for information on several heavy metals and their effects on human health, because Uruguay had only established maximum concentrations for mercury.

The Uruguayan coast is inescapably affected by human activities in Montevideo and Buenos Aires, capital cities on each side of the Rio de la Plata and home to a total of nearly 10 million people as well as industry, sea ports and oil refineries.

Viana thinks there is greater environmental awareness these days, "which has led to economic activities being carried out with greater controls and responsibility."

Furthermore, he said, the economic recession that has affected Uruguay over the past few years has slowed down industrial activity, and therefore reduced the production of toxic waste.

The area hardest hit is Montevideo Bay, because "it acts as a depository of highly contaminated waters from the Miguelete and Pantanoso rivers."

Because it is a semi-closed bay, the recharging of its waters from the Río de la Plata is very slow, which favours the accumulation of heavy metals, fossil fuels and organic material in the sediment, he explained.

According to the United Nations Environment Programme (UNEP), 80 percent of marine environment contamination originates from activities on land, such as waste dumping, oil spills, and alteration of coastal habitats.

Another phenomenon is the introduction of exotic species that are transported in the bilge water of ships arriving from distant ports.

"All of these factors are present in our coastal system. Industrial contamination is a very important source. And not the least of our problems is that the area rivers have very poor water quality," said Viana.

In addition to the very toxic metals, like chrome, others "have the ability to accumulate and increase their concentration as the animal ages." Such is the case of mercury, which can be "bio-magnified", in other words, it increases as it is passed up through the food chain.

As a result, "the last links in the chain are exposed to very high concentrations of toxins," said the biologist. The last of these links is often humans.

In studies conducted in the southern zone of Pajas Blancas, the scientists found corvina with deformed spines. "We don’t know the cause, but according to precedents established in other areas, this phenomenon has been attributed to the presence of contaminants in the environment," Viana said.

According to UNEP, more than 90 percent of the Earth’s living biomass is found in the seas and oceans, and it is estimated that by 2010 around 80 percent of all peoples will live within 100 km of some coast.

Every year, some 21 million barrels (159 litres each) of petroleum – a source of heavy metals – flow into the oceans, originating in street run-off, factory discharge and tanker ships, says UNEP.

Less than one percent of the marine surface is under some degree of environmental protection, while 11.5 percent of land surface is protected.