Risk of cyanobacterial toxins in Riga waters (Latvia)

Riga, the capital of Latvia, is surrounded by several lakes. Being domestic and industrial wastewater recipients, these lakes are eutrophic. One of them, Lake Mazais Baltezers is used for artificial recharge of the groundwater (Quaternary aquifer) through infiltration basins. The water quality of this lake is crucial as the groundwater is eventually used as a source of drinking water. Important cyanobacterial blooms occurred in this lake at the end of summer. These blooms were toxic and microcystin-LR was analysed in the algal biomass. Microcystins were analysed using protein phosphatase inhibition assay and high-performance liquid chromatography. Toxins were analysed in surface water samples as well as drinking water samples to assess the soil cleaning efficiency. This study showed that the Lake Mazais Baltezers was vulnerable due to human activities and its water quality could vary quickly due to cyanobacteria. The soil of this area was not efficient enough to protect the groundwater and the drinking water from toxins during the blooming period (August–September) and it appeared that toxins were not degraded in the soil, which is a cause of concern since the consumption of sub-acute levels may be deleterious to human health. The toxin concentrations indicated that, in the future, the water source should be monitored and that measures should be introduced to control blooms and to remove toxins from the water.