Arsenic accumulation in irrigated agricultural soils in Northern Greece

The accumulation of arsenic in soils and food crops due to the use of arsenic contaminated groundwater for irrigation has created worldwide concern. In the Chalkidiki prefecture in Northern Greece, groundwater As reach levels above 1000 ?g/L within the Nea Triglia geothermal area. While this groundwater is no longer used for drinking, it represents the sole source for irrigation. This paper provides a first assessment of the spatial extent of As accumulation and of As mobility during rainfall and irrigation periods. Arsenic content in sampled soils ranged from 20 to 513 mg/kg inside to 5- 66 mg/kg outside the geothermal area. Around irrigation sprinklers, high As concentrations extended horizontally to distances of at least 1.5 m, and to 50 cm in depth. During simulated rain events in soil columns (pH=5, 0 ?g As/L), accumulated As was quite mobile, resulting in porewater As concentrations of 500- 1500 ?g/L and exposing plant roots to high As(V) concentrations. In experiments with irrigation water (pH=7.5, 1500 ?g As/L), As was strongly retained (50.5-99.5%) by the majority of the soils. Uncontaminated soils (b30 mg As/kg) kept soil porewater As concentrations to below 50 ?g/L. An estimated retardation factor Rf=434 for weakly contaminated soil (b100 mg/kg) indicates good ability to reduce As mobility. Highly contaminated soils (N500 mg/kg) could not retain any of the added As. Invoked mechanisms affecting As mobility in those soils were adsorption on solid phases such as Fe/Mn-phases and As co-precipitation with Ca. Low As accumulation was found in collected olives (0.3-25 ?g/kg in flesh and 0.3-5.6 ?g/kg in pits). However, soil arsenic concentrations are frequently elevated to far above recommended levels and arsenic uptake in faster growing plants has to be assessed.