Emerging Contaminant Imidacloprid in Mediterranean Soils: The Risk of Accumulation Is Greater than the Risk of Leaching

Abstract

Imidacloprid (IMI) is an extensively used neonicotinoid insecticide whose occurrence in the environment is a worldwide problem. Its sorption/transport properties are recognized as one of the key knowledge gaps hindering policymaking regarding its international routine monitoring in soils. Therefore, we studied IMI transport behaviour in Croatian Mediterranean soils using column experiments. Breakthrough curves were analysed using the two-site adsorption model and compared against dimethoate (DIM). Transport parameters were correlated to soil physicochemical properties. The results indicate that IMI shows a high degree of preference for soil organic matter over any other soil constituent. For IMI, the clay did not exhibit any sorption activity, while hematite did act as an active sorbent. Contrarily, hematite increased the leachability of DIM by blocking the active sorption sites on clay platelets. Both hematite and clay sorption acted as type-2 (i.e., rate-limiting) sites. In all soils, IMI exhibited lower short-term leachability than DIM. Combined with a body of data concerning other aspects of IMI environmental behaviour, the results indicate that the risk of accumulation of IMI in the soil is greater than the risk of contamination by leaching. Thus, continuous monitoring of IMI in soils should be incorporated into future soil health protection programs.

Those That Remain: Sorption/Desorption Behaviour and Kinetics of the Neonicotinoids Still in Use

“…It is well known that, from the total neonicotinoid active substance applied in seed treatment, only 2–20% is sorbed by the crop, while the rest is transferred on or through the soil ecosystem [ 12 , 13 , 29 ] (Note that application rates are up to 0.62 kg and 0.57 kg active ingredient per hectare for acetamiprid and thiacloprid, respectively [ 30 , 31 ]). The fate and distribution of those active substances are controlled by the sorption, desorption and degradation processes, which, in turn, depend on soil physico-chemical properties [ 19 , 32 , 33 , 34 , 35 , 36 ]. Generally, soil degradation is faster for acetamiprid, with a half-life in the field of 3 days, compared to 8.8 days for thiacloprid [ 17 ].…”

Those That Remain Caught in the “Organic Matter Trap”: Sorption/Desorption Study for Levelling the Fate of Selected Neonicotinoids

“…By partitioning neonicotinoids between the solid and the liquid phases of the soil, sorption/desorption processes are a decisive factor in determining the fate of pesticides in soil, controlling their availability for other process: sorption by the plant, migration, or degradation [ 9 , 11 , 40 ]. In turn, these processes are affected by the physical and chemical properties of the pesticides and soil [ 42 , 43 , 44 , 45 ]. Typically used in fate and pesticide transport mathematical models, the distribution coefficient K d describes the efficacy of sorption and represents the ratio of the amount of pesticide sorbed to that in soil solution.…”

Environmental Monitoring and Analysis of Persistent Organic Pollutants

“…The fifth article, “Emerging Contaminant Imidacloprid in Mediterranean Soils: The Risk of Accumulation Is Greater than the Risk of Leaching”, brings the results of a Croatian-Polish collaboration in researching the behaviour of the neonicotinoid insecticide imidacloprid in Mediterranean soils [ 5 ]. Although this extensively used insecticide is not considered to be persistent, its frequent occurrence and retention in the environment is of concern worldwide.…”