Differences in sorption behaviour of carbaryl and phosalone in soils from Australia, Pakistan, and the United Kingdom

Sorption of 2 nonionic pesticides, carbaryl (1-naphthyl methylcarbamate) an d phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O,O-diethyl phosphorodithioate), was investigated for 48 soils from Australia, Pakistan , and the United Kingdom. A wide variation in sorption affinities of the so ils to carbaryl and phosalone was observed. The sorption coefficient (K-d) values for carbaryl ranged from 0.19 to 23.0 L/kg in Australian soils, from 0.99 to 59.7 L/kg in Pakistani soils, and from 1.09 to 23.0 L/kg in the UK soils. The K-d values for phosalone ranged from 4.8 to 443 L/kg in Austral ian soils, from 15.5 to 1182 L/kg in Pakistani soils, and from 18.1 to 205 L/kg in the UK soils. To eliminate the effect of variation in organic carbo n content among the soils, the K-d values were normalised to the fraction o f soil organic carbon (K-oc). However, K-oc values for both pesticides vari ed by about an order of magnitude across the soils, decreasing in the follo wing order: Pakistani > Australian > UK soils. Correlation between K-d and organic carbon content of the soils was poor (r(2) = 0.44 and 0.46). The pa rticulate organic C (53 mum-2 mm) was only slightly better correlated with K-d than the total organic C in the <2 mm fraction of the soils. Thus soil organic C content alone is not a good predictor of sorption even for nonion ic pesticides such as carbaryl and phosalone. Caution is needed during extr apolation of overseas data to predict sorption under local conditions.