Levels of microcystins in two Argentinean reservoirs used for water supply and recreation: differences in the implementation of safe levels

Toxic cyanobacterial blooms are an increasing problem in Argentina. The production of cyanobacterial hepatotoxins (microcystins) and their presence in drinking and recreational waters represent a growing danger to human and animal health. Risk management deals with the probability that a certain exposure to toxins will lead to specific health outcomes. Various model schemes for risk management have been portrayed, most of which have some common elements. These include the need for an information base on which to make decisions. Thus, seasonal variability in the concentrations of total microcystins and cyanobacterial cells was studied in two reservoirs: San Roque and Paso de las Piedras. Both reservoirs are eutrophic water bodies and mainly used to supply drinking water and for recreation. Because San Roque is an important recreational spot, the spatial distribution of microcystins was also investigated. Sampling of the San Roque Reservoir occurred from 1998 to 2000 and of the Paso de las Piedras Reservoir from June to December 2002 (late autumn, winter, and spring). Microcystins were identified by LC-MS, and their concentrations were measured using the enzyme-linked immunosorbent assay. These hepatotoxic compounds were detected in all seasons, and even during winter relatively high concentrations were observed. Concentrations in the San Roque Reservoir varied from undetectable to 920 microg/L. On the contrary, in the Paso de las Piedras Reservoir the concentration remained below 1 microg/L, which is the provisional guideline value proposed by the World Health Organization (WHO; Chorus and Bartram, 1999) for microcystin-LR in drinking water. Comparison of cell number and concentration of total microcystins indicated that the phytoplankton in San Roque Reservoir contained more toxic cyanobacterial strains than did the Paso de las Piedras Reservoir. This indicates that the threshold of 2000 cell/mL proposed by WHO as a alert level should be adjusted: it should be reduced for the San Roque Reservoir, whereas it seems appropriate for the Paso de la Piedras Reservoir.