Mercury and Arsenic in aquatic biota from Lake Nahuel Huapi (Patagonia, Argentina) associated with a significant volcano eruption

ARCAGNI, M.; JUNCOS, R.; CAMPBELL, L.M.; RIZZO, A.; ARRIBÉRE, M.A.; RIBEIRO GUEVARA, S.

Vancouver

Encuentro; SETAC North America 35th Annual Meeting; 2014

Globally, volcanic emissions are knownto be one of the major natural sources of trace elements, such as Hg and As tothe atmosphere and via deposition. We investigated the impact of a significant2011 volcanic eruption from the the Puyehue Cordon Caulle volcanic complex innorthern Patagonia with resultant pyroclastic material being deposited on LakeNahuel Huapi 100 kilometers away. Lake Nahuel Huapi, the largest and deepestlake in North Patagonia, was being investigated for metal contamination priorto this eruption. The entire lake surface (557 km2)was completely covered in tephras and other pyroclastic deposits for severalmonths. As a result, we were able to undertake a before-and-after study ofpatterns in As and Hg in the Nahuel Huapi aquatic food web. Samples wereprocessed in the laboratory, freeze dried and analyzed by Instrumental NeutronActivation Analysis in the RA-6 research nuclear reactor (Centro AtómicoBariloche, Argentina). Stable nitrogen isotope (δ15N) analyses were also performed toassess the trophic level of the organisms within the food web. As expected,[Hg] were higher in the non-native salmonids, which presented the highesttrophic level, than in its prey (crustaceans, insect larvae, small fish). Onthe contrary, native Creole Perch had different trends compared to itspreferred prey (cray­fish). Zooplankton presented the highest [Hg] of all thefood web. No differences were observed in the [Hg] in fish, crustaceans,mussels, and zooplankton before and after the eruption. However, lower [Hg]were recorded in snails and insect larvae after the eruption. Varying [As] wereobserved in the different organisms sampled, with [As] decreasing withincreasing trophic level indicating food web dilution. Before the volcaniceruption, zooplankton presented higher [As] than their main predator, the SmallPuyen. Among invertebrates, mollusks had the highest values suggesting Asuptake from sediments. Omnivorous decapods had inter­mediate [As] and predatoryfish had the lowest values, with the native Creole Perch having higher [As]than introduced salmonids. After the volcanic eruption [As] increased inzooplankton and decreased in snails, mussels, and Creole Perch, probably due tochanges in food availability and therefore As availability.