Validation and Application of a 3-Step Sequential Extraction Method to Investigate the Fraction Transformation of Organic Pollutants in Aging Soils: A Case Study of Dechlorane Plus

Abstract

A 3-step sequential extraction method was developed to characterize the “labile,” “stable-adsorbed,” and “bound-residue” fractions of Dechlorane Plus (DP) in aging soils. Afterward, the proposed method was used to observe the transformation of DP fractions during aging. Slight decrease of total DP concentrations suggested there was a rather limited degradation, with only 4.2–8.2% of initial DP having degraded after 260 days. The labile fraction, which indicated the bioavailability of DP, decreased from 25.5% to 8.2%. The bound-residue fraction, usually regarded as a route for detoxification, increased from 0.1% to 18.5%. Model simulations were then developed to investigate the transformation, indicating that transformation rates were inconstant and distinguishable over time. Half-lives of DP were estimated to range from 1325 to 2948 days, indicating its environmental persistence in aging soils. Through Sobol Global Sensitivity Analysis (SGSA), degradation was evaluated to be the most sensitive factor of effecting the DP transformation in aging soils. Furthermore, the fsyn values increased from 0.26 to 0.37 in the labile fraction and decreased from 0.25 to 0.18 in the bound-residue fraction. The observed stereoselectivity difference might be the cause of the stereoselective accumulation of DP in terrestrial organisms.

Source, fate and budget of Dechlorane Plus (DP) in a typical semi-closed sea, China

“…This finding differs from previous outputs of black carbon (BC) and heavy metal in the BS revealing the absolutely dominant role of sedimentation (Fang et al, 2015;Liang et al, 2018). DP were relative persistence in the environment (Cheng et al, 2019;Huang et al, 2020). However, previous study had also found dechlorination (DP [-Cl þ H] and ] degradation products) and other unidentified DP-degradation products by photodegradation (Canada, 2019).…”

Fractions Transformation and Dissipation Mechanism of Dechlorane Plus in the Rhizosphere of the Soil–Plant System

“…However, the hydrophobicity of DP (log K ow = 9.0) hindered mobility to the extent that it contributed very little to dissipation. Owing to these effects, the half-life of DP was greatly shortened to 105 days in the root compartment for the S1 soil, while this value was 1325 in the unplanted soil estimated by our previous study …”

“…This procedure was repeated three times, and the combined extracts were filtered through a 0.22 μm PTFE syringe filter and concentrated to 1 mL for instrumental analysis. The fractions of DP in soil were determined using a 3-step sequential extraction method described in our previous study . Analysis of DP was performed with GC–MS (a Thermo DSQ II system) operating in the electron capture negative ionization (ECNI) mode.…”

“…The equations describe fraction transformation of DP in the rhizosphere are modified based on our previous study: where L s , S , and B represent the concentrations of labile, stable-adsorbed, and bound-residue DP in soil, respectively [ng/g]; K i ( i = 1, 2, 3, ···) represents the rate coefficient for transformation of DP between different fractions (day –1 ).…”

“…Dissipation of organic pollutants in soil has generally been assessed by the amount of total solvent-extractable material, ignoring the heterogeneous nature of the soil . Organic pollutants in soil components generally consist of 3 main fractions: labile, stable-adsorbed, and bound-residue . The labile fraction contains the fraction dissolved in soil water, and the rapid absorbing–desorbing fraction at the soil–water interface.…”