Sorption and genotoxicity of sediment-associated pentachlorophenol and pyrene influenced by crop residue ash

Abstract

Purpose The bioavailability and potential toxicity of sedimentassociated organic compounds are affected by sorption processes. The particulate matter (ash) from field burning of crop residues is one of the primary sources for environmental black carbon, which is regarded as supersorbent for organic contaminants and may reduce their ecotoxicity. This study aimed to investigate the influence of ash on sedimentassociated organic pollutants' potential toxicity. Materials and methods Pentachlorophenol (PCP) and pyrene (PYE) were chosen as the target organic pollutants, earthworms (Eisenia fetida) were used to evaluate the genotoxicity of contaminated sediments in the exposure experiments, and the genotoxicity (expressed as DNA damage) was quantified by comet assay. Sediments amended with different levels of ash (1%, 3%, 5%, and 10%) were selected as the sorbent to investigate the influence of ash on the sorption and genotoxicity of sediment-associated organic compounds. In order to study the toxic effect of ash, the ash-amended sediments without pollutants addition were adopted as exposure systems in the comet assay. Results and discussion The sorption capacity for PCP and PYE increased with ash content in the sediment. The high adsorptivity of ash was attributed to the black carbon contained in the ash, which is in line with many previous studies. When spiked at a concentration of 200 μg/kg, both PCP and PYE exerted significant genotoxic effect on earthworms. The genotoxicity of sediment-associated pollutants decreased as the ash content in sediment increased. The DNA damage in the 5% ash-amended exposure showed no significant difference with that in the control exposure, probably due to the strong sorption capactiy of ash, which decreased bioavailability as well as toxicity of sediment-associated pollutants. However, the 10% ash treatment had a higher DNA lesion than that in the 5% charadded exposure. This may have been caused by the genotoxic compounds and high alkalinity contained in the ash. Conclusions Addition of ash increased sorption and inhibited the genotoxicity of sediment-associated organic toxicants. When added at a high rate (e.g., 10%), ash could also exert genotoxic effect. As field burning is a common land-cleaning method in many agricultural areas, the ecological influence of ash should be given much attention in the future study. More research should be conducted to better understand the mechanism of toxic effect of ash.

Adsorption Behaviour of Pymetrozine by Four Kinds of Biochar from Aqueous Solution

“…It has been reported that surface area, porosity and functional groups of BC play important roles in the sorption of organic pollutants (Cui et al 2009;Lou et al 2011). The characteristics of BCs, such as surface area and porosity, helped in capturing pymetrozine through surface coverage, multi-layer adsorption and condensation in capillary pores.…”

Impact of Biochar on Earthworm Populations: A Review

“…Sorption of organic pollutants to the char was determined by evaluating the genotoxicity to the earthworm Eisenia fetida. The charred rice crop residue, containing some black carbon, at low mixture rates (1%, 3% and 5%) reduced genotoxic damage of the organic pollutants, however at a mixture rate of 10% the rice-char itself caused genotoxic damage to the earthworm [47].…”

“…The neutralizing of soil pH was provided as a reason why earthworms were not deterred from burrowing into the charcoal-soil mixtures [46]. The prospect of using char from slash-and-burn management practices in rice crops in China for reducing environmental contaminants was evaluated [47]. Rice crop residue was charred in the laboratory to mimic field slashand-burn residue and mixed into sediment of 4.7% C and a pH of 6.9.…”

“…Even though the chars used in these studies [46,47] are both considered slash-and-burn residue, the materials are quite different as indicated by the high C content of the wood-derived char-soil mixture (39% C) versus the low C of the rice-derived char-soil mixture (11% C). Therefore, one could expect different responses due to the inherent differences in black carbon chemistries.…”

“…Although we cannot discount the potential use of biochar for digestive purposes by field populations, laboratory studies certainly showed that earthworm behaviors were altered, and soil ingestion was reduced. A few of these laboratory studies demonstrated that some biochars are likely to be potential toxins [47] but lethal results likely depend on amendment rates [12]. Beesley and Dickenson [14] did show that leaching of potential toxins, including Pb, As, and Cu, was increased with biochar application, though the biochar might not have been the direct source of these elements.…”