Sj. Stangroom et al., Abiotic behaviour of organic micropollutants in soils and the aquatic environment. A review: I. Partitioning, ENV TECHNOL, 21(8), 2000, pp. 845-863
Recent research has confirmed the significance of organic carbon (OC) as th
e key sorbent for hydrophobic organic chemicals (HOC), as well as for many
polar compounds. However, the triazine herbicides exhibit a variable affini
ty for soil organic matter (SOM) which is attributed to the extent of humif
ication of the organic fraction. Charge transfer mechanisms are important f
or triazine sorption to OC and either proton or electron transfer may accou
nt for the reaction mechanism with humic acids. For many uron herbicides (e
.g, chlorotoluron, metabromuron chloroxuron, defenoxuron), sorption correla
tes with SOM. However, specific interactions between uron herbicides and a
limited quantity of active constituents within SOM have also been proposed
to explain deviations from sorption linearity at low herbicide relative con
centration. Other studies indicate that isoproturon sorbs to organic colloi
ds in solution and that a sorption threshold to SOM may be operative. Below
the threshold, isoproturon appears to sorb predominantly to clays, indicat
ing the presence of a limited number of 'active' sorptive sites within clay
minerals. Research suggests that pesticide interactions with clay minerals
may be influenced by near-surface day geometry; the accessibility of the s
orbing region of the sorbate to the active site of the clay; the identity o
f exchangeable cations on the clay and solution electrolytes. These recent
studies indicate that interactions between micropollutants and soils and se
diments often need to be evaluated on a compound-specific basis. This is es
pecially the case for polar compounds which may partition to these environm
ental phases by diverse mechanisms.