Influence of hail suppression systems over silver content in the environment in Aragón (Spain). II: Water, sediments and biota.

The silver content in soils in the area in the surroundings of the Gallocanta Lake (Aragón, NE Spain) is lower than expected considering the estimated silver emission during the last 50 years by hail suppression systems. To understand the silver accumulation processes, selected water (4 surface, 3 groundwater), biota and sediment (6 surface sediments and 3 cores from Gallocanta and Campillo de Dueñas Lakes and Used Reservoir) samples have been analysed. An essay comparing the growth of wheat in pots with different silver iodide concentrations has been carried out. Finally, silver content in 7 tissues from two sheep that graze in areas both with and without hail suppression systems during 6-8 years were analysed. Our results show that after 50 years of silver iodide emissions to the atmosphere, silver accumulation in the waters and sediments of the lowlands, including some wetlands of high ecological value, has not been significant. Sediment cores did not show any peaks associated to silver emission. We propose that constant absorption of silver by plants could explain the low concentration in water and sediments. Crops and grass could accumulate the excess silver, as both wheat and sheep are able to absorb significant amounts of silver. These bio - accumulation processes could have helped to avoid a progressive environmental deterioration of the surroundings of the Gallocanta Lake. However, this hypothesis should be corroborated and quantified by further research on the analysis of natural and agricultural areas under the influence of hail suppression systems.