Laboratory study of retention and release of weak acid herbicide MCPA by soils and sediments and leaching potential of MCPA

Abstract

MCPA sorption and desorption in five surface soils (denoted as A1-5), three bottom sediments (S1-3), two river sediments (L1-2) and one subsurface soil (SS) at two initial concentrations in aqueous solution – C₀ = 0.5 and 10 mg/l were studied. No significant effect of the initial concentration on MCPA equilibrium distribution between soil/sediment and aqueous solution was observed. The difference between distribution coefficient K_D at C₀ = 0.5 mg/l and K_D at C₀ = 10 mg/l was found only in the case of one bottom sediment (S2). A simple regression analysis between K_D at C₀ = 0.5 and 10 mg/l and soil/sediment properties indicated that the most important property which determined the variation in MCPA sorption is organic carbon (r = 0.886*** and r = 0.926***, respectively). Similarly, desorption of MCPA was inversely proportional to organic carbon content of the soils and sediments used (r = –0.862* and r = –0.842**). These observations showed that MCPA sorption and desorption in soils and sediments were primarily controlled by organic components of the geosorbents used. Overall, the percentage of MCPA sorption in soils and sediments was low (P_sorp ≈ 3–53%; K_D = 0.077–2.827 l/kg) and the percentage of MCPA desorbed was relatively high (P_des ≈ 11–70%), especially in the soils and sediments with lower organic carbon content. The experimental results and calculated values of groundwater ubiquity score GUS and relative leaching potential index RLPI imply that MCPA is very mobile in all the surface soils and has a potential to contaminate groundwater.