Billions of tons of heavy metals are emitted annually by factory smokestacks and sewers. These elements are harmful to living beings and damage the hydrosphere by polluting rivers, lakes and seas. It is difficult to find part of any ocean without this pollution, even in the remotest locations.
A study funded by a scholarship from FAPESP and conducted by Caio Vinícius Cipro, a postdoctoral fellow of the University of São Paulo’s Oceanographic Institute (IO-USP) in Brazil, identified traces of heavy metals in several invertebrate, fish and bird species that inhabit the Kerguelen Islands, an archipelago in the southern Indian Ocean belonging to the French Southern & Antarctic Territories.
The study was conducted in partnership with French researchers in one of the world’s most isolated places, a group of 300 islands halfway between Africa and Australia, 4,000 km south of India, and 2,000 km north of Antarctica.
The archipelago is of volcanic origin and covered by glaciers, rock, and solidified lava from the long-dormant Mount Ross, its highest peak. The vegetation is tundra, battered by incessant freezing winds. A research station has some 120 residents in summer and fewer than half that number in winter.
Kerguelen’s barren landscape contrasts with the wealth of its marine life. Its waters are rich in food for colonies of king penguins, elephant seals, sea lions, albatrosses, petrels, dolphins and whales. At first glance, the waters are free from any kind of human pollution.
“After my PhD, I spent almost five years at the University of La Rochelle in France, with funding from French organizations, FAPESP, and the Brazilian government’s Science Without Borders Program. In 2013, I was invited by my French supervisor Paco Bustamante to work with a collection of samples and datasets gathered years earlier in Kerguelen. In 1998, Bustamante had found an accumulation of cadmium, copper and zinc in octopuses from Kerguelen, but there was much more to investigate,” Cipro said.
“In the French Antarctic program, the study of collected material doesn’t have to be done by the professionals who do the field work. In our case, we analyzed samples of birds, fish and various invertebrates. The idea was to verify the base concentrations for upper-trophic-level organisms.”
In 2014, Cipro published the first part of his research in Polar Biology, showing contamination of the white-chinned petrel (Procellaria aequinoctialis) by copper, selenium and zinc. The second part, published recently in the same journal, shows that fish and marine invertebrates are contaminated by metals.
In addition to cadmium and mercury from natural sources, he found metals resulting from effluent discharged by factories located more than 10,000 km away. Microparticles of heavy metals released into the environment reach the oceans and are absorbed near the surface by zooplankton. Microscopic invertebrates that form the foundation of the marine food chain, zooplankton are eaten by primary consumers such as mollusks, crustaceans, smaller fish, and the largest living animals, Mysticeti, like the Blue whale.
Squid, mussels, crustaceans and fish are eaten by secondary consumers. Each particle of metal that enters the marine food chain ends up accumulating in the tissue of animal groups that occupy its upper levels: fish species such as tunas and sharks, birds, and mammals such as seals, sea lions, dolphins and orcas.
According to Cipro, there are few studies that show contamination of lower-trophic-level organisms by heavy metals in remote ecosystems.
“The aim of our new study was to obtain data on the accumulation of heavy metals in invertebrate organisms such as mussels and squid,” he said. “The data we obtained can support research on higher trophic levels.”
The species collected represent a substantial cross-section of Kerguelen’s ecological groups. The sizes of the animals sampled are within the range of the prey preferred by apex predators in the area, more specifically the various species of seabirds that inhabit the islands.
“If we compare contamination data for all ecosystems, we get interesting results,” Cipro said. “Cadmium levels in the mussels that inhabit a broad bay with the largest colonies of marine birds in Kerguelen are higher than in mussels elsewhere in the islands. The evidence suggests the cadmium in these mussels comes from seabird colonies in the Gulf of Morbihan, the site of Port-aux-Français, the largest human settlement on the island with a population of 40 in winter and 120 in summer.”
The researchers found a correlation between the size of the mussels collected at low tide and the amount of cadmium they contained. “The positive correlation between cadmium levels and mussel size clearly suggests bioaccumulation of this heavy metal in the bivalves’ tissue as they grow,” Cipro noted.
When heavy metals from natural sources and industrial waste reach the sea, they are usually absorbed by marine organisms. Some organisms, like squid, absorb a great deal. Cephalopods, the group to which squid and octopus belong, are notorious bioaccumulators of several chemical elements.
“Cadmium levels found in squid species from Kerguelen were among the highest for all species analyzed in this study,” Cipro said.
Different contamination profiles
In the previous study, which focused on petrels, Cipro and colleagues found high levels of mercury in liver tissue (58.4 micrograms per decigram on average) and of cadmium in kidney tissue (65.7 µg/dg on average).
“One possible explanation is that these birds follow fishing boats, which throw away unwanted tissue from the catch and could expose them to higher levels of contamination,” Cipro said.
Very high levels of heavy metals were also found in some species of zooplankton, which is quite unusual for the species analyzed. “An example is Themisto gaudichaudii, a small planktonic crustacean, with far higher cadmium levels than several fish species, which should theoretically be more exposed to this heavy metal,” Cipro said.
He added that concentrations of heavy metals in crustaceans living in continental shelf waters are far higher than in the crustaceans that inhabit Kerguelen’s coastal waters.
“In the course of the study, we found that in the lower trophic levels, each invertebrate niche, mollusks or crustaceans, displays contamination in different amounts and with different profiles,” Cipro said.
Cipro and his French colleagues are now investigating which bird species are most susceptible to heavy metal accumulation. “The results will be published shortly, with an analysis of 26 seabird species,” he said.
Source : By Peter Moon | Agência FAPESP