Fish locally known as el ñato, the canchimala and the canchimala blanca are part of the regular diet and economy of the Colombian port city of Buenaventura. However, after assessing 1,285 of these fish and other 62 fish species of 27 families, the Universidad Nacional de Colombia (UNal) in Palmira Ecology and Water Pollution Research Group (ECONACUA, for its Spanish acronym) discovered 540 specimens (42%) with total mercury concentrations surpassing 0.2 micrograms per gram.
UNal-Caribbean Ph.D. Sciences candidate Andrés Esteban Molina Sandoval says that according to the World Health Organization (OMS), these mercury levels could pose a threat to vulnerable populations, such as pregnant women, children and the elderly which eat fish regularly.
Using a method proposed by the U.S. Environmental Protection Agency the researchers estimated the amount of fish in the identified conditions which could pose a threat to the population.
“A person of the aforementioned groups with a weight of 70k should not eat more than 22g of canchimala blanca, 25g of canchimala or 27g of ñato fish a day,” claims Molina.
On the other hand, the cajero fish (Larimus argenteus), a much sought out species but with a low fishing rate, the total mercury level was over 0.5 mg/g. According to the OMS, this amount surpasses the threshold and could also pose a possible threat for any person.
UNal- Bogotá Faculty of Medicine Professor David Andrés Combariza Bayona says mercury is eliminated from the body in a very slow manner and the nervous system is where it is mostly deposited when there is biological accumulation.
“High mercury concentrations produce vision alterations, lack of memory, tremors and mood swings. When the levels are high, they also produce kidney issues. The effects could be more serious in fetuses when pregnant women have consumed important amounts of mercury-tainted food,” he adds.
The research project determined that the pollution of the Bay of Buenaventura could have an impact on the whole ecosystem due to the bioaccumulation and bioamplification of mercury, the former is produced over time, when the mercury concentrations surpass the levels where organisms can naturally cleanse the element and the latter, when the metal passes from one chain food link to another.
Recovering and preserving rivers and water streams as well as other broken-down strategic ecosystems were part of the request sheet presented by the population during a civil strike of 2017, which blocked all port activities for 21 days.
As a result of the strike, the Office of the Mayor of Buenaventura said it will work with other institutions and organizations to work against deforestation and jungle degradation and begin an adequate management and control of dangerous solid waste, and temporary revoke mining licenses with the purpose of avoiding more damage to the natural resources of rivers, mangroves, tidelands, and the bay. This commitment package agreed with the community will see an investment of COL$39,000 million.
The fish analyzed were obtained in four samplings carried out during the dry and rainy seasons in representative locations and outpours of the Dagua and Anchicayá Rivers and the sea.
The journeys lasted for almost a week and the researchers accompanied artisanal shrimp fishermen. “We worked with local fishermen who used trawl fishing which is not as selective as hook fishing,” said Molina.
Fish and sediments better reflect the water pollution due to the high incidence of tide variations on the seawater. The research project focused on species with low mobility due to their potential to assess the amounts of mercury accumulated during their lifetime in a particular ecosystem.
“The samples were frozen and taken to the laboratory for better preservation. Some species are different for very specific details, such as dental structures or the number of spines in the gills,” he added.
After identifying the species, the specimens were measured and weighed to classify them into adults and juveniles and to assess their health status. The following step was to peel off the skin and remove the muscle using non-metallic knives (to avoid contaminating the samples). The samples were then freeze-dried and then they introduced a direct mercury analyzer.
To analyze the data obtained they also had the support of Universidad Santiago de Cali Professor Pilar Cogua Romero. The project background was a study carried out in 2009 with the species Mugil cephalus, Stellifer fuerthii and Cathorops multiradiatus. Professor and Director of ECONACUA Guillermo Duque, says this was a preliminary sampling to have an indication of what was occurring and then propose the current project.
“We discovered a process of mercury bioaccumulation with genotoxicity effects which produced abnormalities in the nuclei of fish erythrocytes,” he said.
As the research project also approached the presence of mercury in invertebrates of the bay, the researchers are progressing on the analysis of the pollution flow in the food chain in order to compare the results with future monitoring in other areas of the Pacific region.
“These are projects that have been carried out scarcely in tropical areas and will serve as a baseline to be cognizant of the environmental situation,” said Duque. The research project will also provide input to the environmental authorities to embark in more projects directed to mitigate the pollution of water ecosystems of the region.
For Molina, although the Bay of Buenaventura is often linked to pollution, its biodiversity is comparable to other tropical coastal areas. And adds: “The country should pay attention to the discoveries of the research carried out by UNal, as Colombia cannot place the ecological potential of the region at risk, it needs to be recovered and preserved.”
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