Toxin contamination of surface and subsurface water bodies connected with lake Vico’s watershed (Central Italy)

Cyanotoxins are a new class of freshwater risk factors widespread all over the world, whose sanitary implications are not yet fully understood. The environmental destiny of these toxins produced by many cyanobacterial species holds consequences not only for water bodies where blooms occur, but also for public water sources. Drinking water wells in fact can be contaminated by toxins able to migrate through groundwaters feeding lakes and ponds hosting toxic blooms. In Italy cyanobacterial toxic blooms are largely diffused in lakes, fish ponds, channels and even along sinuous rivers, but their health consequences are still poorly investigated. In order to evaluate the contamination degree of groundwaters around lakes with toxic algal populations, a multidisciplinary study was set up during 2005-2007 interesting all the recharge area of the Lake Vico basin, a volcanic crater lake in Central Italy hosting a Planktothrix rubescens population producing the hepatotoxic microcystins. The lake, as part of a natural reservoir, has noticeable environmental and landscape value. Drinking water source for two towns, it has no tributaries and a long renewal time, with tendency to accumulate polluting substances. During a 18 months monitoring plan, five stations on the lake and eleven wells in the drainage basin were monthly sampled to allow the study of P. rubescens population dynamics and the definition of the groundwater circulation scheme, with the quantitative and qualitative characterization of storage and eutrofization state both of the lake basin and the subsurface hydrogeological system. Moreover, a statistical methodology was developed to locate and evaluate the nutrient loads over the study area, identifying the polluting sources on soil and on surface water, also integrating data available from the anthropic and natural systems (climatic data, soil gradation, surface and subsurface water circulation). The groundwater and lake water data and the evaluation of the nutrient amount confirmed the high pollution degree of the stratum feeding the lake. The microcystin concentration in the lake reached values up to 6.5 µg/L, with high concentrations found in October at 15 m depth and fish contamination in spring. Five different MCs were detected. During the autumn-winter months the microcystins also reached ten out of eleven water wells, reaching values up to 123 ng/L and confirming the ability of these pervasive toxins to migrate through groundwater as yet detected in other lakes of Central Italy. Possible recommendations for Lake Vico restoration should be focused on reduction of the nutrient levels deriving from agricultural activities and civil drains. This reduction could be achieved through interventions focused on agronomical technique improvement and on sewage discharging regulation.