Effect of suspended soil material and pig slurry on the facilitated transport of pesticides, phosphate and bromide in sandy soil

The colloid-facilitated transport of pesticides and other pollutants to gro undwaters is a source of concern to authorities in the European Union and o ther countries. It has been suggested that colloids are good sorbents for p esticides and other pollutants, and it is now suspected that the spreading of animal manures increases the potential for colloid-facilitated transport . In experiments in lysimeters of sandy soil to which phosphate, triallate, chlordane and bromide were applied to the surface, the first concentration peaks of the other chemicals always appeared before that of bromide, sugge sting that their transport was facilitated by colloidal or suspended soil m aterial. Chlordane was transported only when sorbed on suspended soil mater ial and was associated most closely with the coarsest of suspended material (>1.2 mum), possibly because it contained the most organic matter. Phospha te was also associated with this class but probably because of the clay it contained. Applying pig slurry to the soil significantly increased the loss of triallate from the lysimeters but not that of chlordane, probably becau se the latter was held strongly by the soil's organic matter. The loss of t riallate was not associated with that of any of the size classes of suspend ed soil material, which may imply that it was transported in association wi th dissolved or colloidal organic matter. Neither the pig slurry nor an equ ivalent amount of inorganic phosphate significantly increased the loss of p hosphate. The amounts of triallate and chlordane applied were 100 times the standard agricultural applications, but the largest concentration of chlor dane measured was still less than the European Union limit of 0.1 mug l(-1) . That of triallate was greater than the limit but would almost certainly h ave been less than it with the standard application. The greatest cumulativ e losses of phosphate, triallate and chlordane were, respectively, 1%, 0.00 3% and 0.00002% of the amounts applied. All the results suggest there is on ly a very small pollution risk to groundwaters from the pesticides and phos phate.