Sorption and Mobility of Ivermectin in Different Soils

Abstract

Avermectins are widely used to treat livestock for parasite infections. Ivermectin, which belongs to the group of avermectins, is particularly hazardous to the environment, especially to crustaceans and to soil-dwelling organisms. Sorption is one of the key factors controlling transport and bioavailability. Therefore, batch studies have been conducted to characterize the sorption and desorption behavior of ivermectin in three European soils (Madrid, York, and artificial soil). The solid-water distribution coefficient (K(d)) for ivermectin sorption to the tested soils were between 57 and 396 L kg(-1) (determined at 0.1 microg g(-1)), while the organic carbon-normalized sorption coefficients (K(oc)) ranged from 4.00 x 10(3) to 2.58 x 10(4) L kg(-1). The Freundlich sorption coefficient (K(F)) was 396 (after 48 h) for the artificial soil over a concentration range of 0.1 to 50 microg g(-1), with regression constants indicating a concentration-dependent sorption. The obtained data and data in the literature are inconclusive with regard to whether hydrophobic partitioning or more specific interactions are involved in sorption of avermectins. For abamectin, hydrophobic partitioning seems to be one of the dominant types of binding, while hydrophobicity is less important for ivermectin, which is probably due to the lower lipophilicity of the molecule. Furthermore, the presence of cations such as Ca(2+) leads to decreasing sorption. Thus, it is presumed that ivermectin binds to soil by formation of complexes with immobile, inorganic soil matter. In contrast to abamectin, hysteresis could be excluded for ivermectin in the studied soils for the evaluation of sorption and desorption. The sorption mechanism is highly dependent on physicochemical properties of the avermectin.

Fate and effects of ivermectin on soil invertebrates in terrestrial model ecosystems

“…Physico-chemical properties of ivermectin have been summarised recently by Liebig et al (2010). Noteworthy is its log Koc value (4.4; Krogh et al 2008), which indicates a high adsorption potential in soil. Ivermectin was applied via artificial slurry made from spiked cow dung.…”

Chronic toxicity of ivermectin to the benthic invertebrates Chironomus riparius and Lumbriculus variegatus

“…With organic carbon normalised sorption coefficients (K OC ) ranging from 12,800 to 25,800 (Halley et al 1989;Krogh et al 2008a), sorption of ivermectin to soil and organic matter is high. Therefore, erosion of ivermectincontaining particulate matter and direct excretion of treated pasture animals into small watercourses, ponds or lakes are the most relevant entry pathways into the freshwater environment (Kövecses and Marcogliese 2005).…”

Bioaccumulation of ivermectin from natural and artificial sediments in the benthic organism Lumbriculus variegatus

“…Although pH could influence the sorption strength by affecting adduct formation and complexation of compounds, this is probably not the case for ivermectin which is unionized at pH values between 5 and 9 (Krogh et al 2008). …”

“…For example, pH and cation exchange capacity have an effect on the formation of adducts and complexation with inorganic soil matter constituents (Fent and Looser 1995;Oppel et al 2004). Krogh et al (2008) measured log K oc values of ivermectin in different soils and found that they were not related to the OC content of those soils, which indicates that the potential of ionic binding of ivermectin to soil does also depend on other sediment characteristics besides OC (Krogh et al 2008). Therefore, our hypothesis for study B was that sediment characteristics influence the availability of ivermectin for worms.…”