Uptake and bioavailability of persistent organic pollutants by plants grown in contaminated soil

Abstract

This paper assesses the uptake of persistent organic pollutants (POP’s) into plants. In particular, uptake of α-endosulfan, β-endosulfan and endosulfan sulfate from lettuce. The lettuce plants were grown on compost that had previously been contaminated at 10 and 50 μg g⁻¹ per POP. The soil was slurry spiked by adding the appropriate amount of POP in acetone in an approximate ratio of 1 ∶ 2, w/v soil ∶ solvent. The solvent was left to evaporate at ambient temperature for 24 hours. Lettuce plants were grown under artificial daylight for 12 hours a day. The influence of soil ageing on the recovery of POP’s from spiked soil samples was also assessed. The average recovery of endosulfan compounds from slurry spiked soil (10, 20 and 40 μg g⁻¹) was consistent (92.9 ± 4.4% for n = 9). However, ageing of endosulfan compounds on the slurry spiked soil resulted in lower recoveries (average losses were 12.5% after 14 days ageing of slurry spiked soil). The uptake of POP’s was assessed by measuring the amount of endosulfan compounds in roots and leaves from lettuce plants after 10, 20 and 33 days. In addition, control plants grown in uncontaminated soil were monitored and analysed. It was found that endosulfan compounds were present in the roots of all lettuce plants irrespective of soil spike level or age of plant. In the 33 day lettuce plants where the soil was spiked at the highest level (50 μg g⁻¹) endosulfan compounds were determined in the leaves. The root to leaf ratio was found to be 3.1 for α-endosulfan, 46.0 for β-endosulfan, and 24.3 for endosulfan sulfate. Spiked lettuce samples were subjected to in vitro gastrointestinal extraction to assess the bioavailability of endosulfan compounds. No detectable endosulfan compounds were determined in the gastric extracts while small quantities (range 0.06–0.12 μg g⁻¹) were found in the intestinal extraction. All samples (soil and lettuce) were extracted using pressurised fluid extraction and analysed using gas chromatography with mass selective detection.