Arsenic transfer from As-enriched soils to water systems

Resumo

The potential risk of As mobility to water bodies was evaluated in the Anllóns River basin (Galicia, NW Spain) where Au-As mineralizations have been historically exploited. 50 soil samples of C horizons were sampled on a 1 km x 1 km grid along the river course, including the mineralized zone, and were submitted to an exploratory anal- ysis, followed by a detailed study of the 9 soils with the highest As concentration. Total As ranged between 2 and 489 mg kg-1. As leachability using the standard leaching method DIN 38414-S4 was < 0.03 % of total As. Frac- tionation studies indicated that As is mainly bound to crystalline Fe oxides, justifying its low solubility. As mobility increased up to 124 times by increasing pH or liquid:solid ratio, with respect to the DIN method, whereas the addition of 10 mM phosphate increased As leachability up to 1,000 times, and this effect increased up to 2.3 times with contact time. Although standard leaching methods provide useful information in terms of legal limits or com- parable data between laboratories, they can underestimate As mobility under more realistic scenarios, such as those occurring in soils affected by mining activities or contaminant spillages.