Bioavailability Of Pollutants In Soils Research Articles

Development of a whole-cell biosensor for detecting organophosphorus pesticide methyl parathion in the farmland soil

The evaluation of the bioavailability of pollutants in soil is crucial to accurately assess the pollution risk, and whole-cell biosensor is one of the important tools for such evaluation. This study aimed to develop a novel whole-cell biosensor for the detection of methyl parathion in soil using. First, a whole-cell biosensor was constructed by the screened methyl parathion hydrolase mpd gene, the existing specific induction element pobR, and the pUC19 plasmid skeleton. Then, the detection method of methyl parathion in soil extracts was established using 96-well microtiter plate as carrier and five whole-cell biosensors as indicator. The method was applied in the detection of methyl parathion in tested and field soil extracts. Taking E. coli DH5α/pMP-AmilCP with the best detection performance as an example, this biosensor had a detection limit of 6.21-6.66 µg/L and a linear range of 10-10 000 µg/L for methyl parathion in four soil extracts. E. coli DH5α/pMP-RFP and E. coli DH5α/pMP-AmilCP methods have good detection performance for the analysis of methyl parathion in soil extract samples. This biosensor method can help to quickly assess the bioavailability of methyl parathion in soil, and thus help to understand the risk of soil pollution caused by organophosphorus pesticide methyl parathion.

Role of Root Exudates on the Soil Microbial Diversity and Biogeochemistry of Heavy Metals.

Due to extensive industrialization and escalation in pollution, the world is facing problems related to soil heavy metal pollution. The traditional ways of soil remediation are neither feasible nor cost-effective in most of the real-world scenarios, where metal concentration is relatively low in soil. Therefore, phytoremediation using plants and plant secretions to remediate heavy metal-contaminated soil is recently getting more attention. The plant root exudates act as an ecological driver in the rhizospheric region where they influence and guide the microbial community to function in such a way that can be advantageous for plant growth. They also promote phytoremediation process by altering the bioavailability of pollutants in soil. Root exudates affect the biogeochemical properties of heavy metals as well. In this review, existing literature on the role of root exudates (natural as well as artificial) on the phytoremediation of heavy metal-contaminated (particularly lead) soil is reviewed. The effect of root exudates on the biogeochemistry of lead in soil is also discussed.

Effects of Straw Return and Moisture Condition on Temporal Changes of DOM Composition and Cd Speciation in Polluted Farmland Soil.

Straw return can improve soil quality and change the mobility and bioavailability of pollutants in soil. Elevated cadmium (Cd) contents in farmland soils were often reported. However, the impacts of straw-derived dissolved organic matter (DOM) on Cd speciation in soil remain poorly understood. In this study, the effects of straw return and moisture condition on temporal changes of DOM composition and Cd speciation in farmland soils were explored through a laboratory incubation experiment. The humified components of DOM were negatively correlated with exchangeable, carbonate-bound, and Fe-Mn oxide-bound Cd (p < 0.01), while its protein-like component was negatively correlated with residual Cd (p < 0.01). It was found that selected fluorescence parameters could be used to predict temporal changes of Cd geochemical fractions. Straw addition led to increases in soil DOM content during the first three days of the incubation. Flooding should be avoided in the first three days following the straw application to reduce the risk of DOM-facilitated Cd mobilization.

Effects of earthworm casts on sorption-desorption, degradation, and bioavailability of nonylphenol in soil.

Up to hundreds of milligrams per kilogram (dry weight) of nonylphenol (NP) reportedly entered the soil and sediment through the agricultural reuse of biosolids, pesticide application, etc. Organic pollutants in soil could not only further trigger groundwater contamination via leaching (that highly depends upon sorption-desorption and degradation phenomena) but also harm food safety by crop uptake (that mainly rests with the bioavailability of pollutants in soil). Thus, we first investigated the effects of earthworm casts (EWCs) on the sorption-desorption, degradation, and bioavailability of NP in soil under laboratory microcosm conditions, and then, analyzed the FT-IR spectra of EWC and soil samples (with and without EWC). The application of EWC could notably increase the sorption capacity of soils for NP and in turn significantly inhibited the desorption of NP from soil; responsively lengthened the half-time of NP in the soil; and reduced the uptake and translocation of NP in tomato seedlings and promoted their growth during the first 3weeks. Finally, FT-IR spectra of EWC and soil samples indicated that the application of EWC increased the content of N, P, and organic matter in soil.

Reverse flow of urban pollutants in sewage irrigated crops in developing countries

Dwindling fresh water supplies in developing countries have led to increased interest in exploring alternative irrigation water sources including untreated or partially treated wastewater. Wastewater originates from a variety of sources including domestic sewage, mixed with industrial effluents, and stormwater. Wastewater irrigation benefits farmers and other stakeholders through better crop yields owing to reliable water and nutrient supply and pollution reduction of rivers and other surface water bodies. However, it poses health risks to farmers and consumers alike due to pathogens, build-up of chemical pollutants especially heavy metals in soils and groundwater contamination. A very small proportion of sewage water (SW) is treated in a few working sewage treatment plants (STPs) in developing countries. Many existing STPs are running above the capacity and only partially treat SW. Many studies on SW in developing countries show the presence of high metal and metalloid concentrations beyond maximum permissible limits. Likewise, several studies evidence increased concentrations of heavy metals in both groundwater and surface waters in developing countries. Repeated use of SW for irrigation may result in accumulation of heavy metals in soils, which can enter the food chain. Review of pertinent literature demonstrates heavy metal accumulation in soils and eventually in edible portion of crops grown in peri-urban areas. Site specific best management practices aimed at curtailing the bioavailability of pollutants in soil and eventual uptake and translocation to edible parts of the crops are required. New STPs and upgradation of the existing STPs are the need of hour. Developing countries need to develop pretreatment standards for industrial waste discharged to the STP collection systems.

Effects of the amendment of biochars and carbon nanotubes on the bioavailability of hexabromocyclododecanes (HBCDs) in soil to ecologically different species of earthworms

Biochar is a promising material used in soil amendment and carbon nanotubes may enter soil due to its increasing application. These carbonaceous materials may change the bioavailability of pollutants in soil. In this concern, 0.5% w/w multi-walled carbon nanotubes (MWCNTs) and 3 corn-straw biochars acquired at different pyrolyzing temperatures were used in soil amendment and their influences on the bioavailability of hexabromocyclododecanes (HBCDs), a brominated flame retardant, to 2 ecologically different earthworm species were studied. The amendment of 4 carbonaceous materials all reduced the bioaccumulation of HBCDs in earthworms by 18.2%–67.3%, which varied depending on the type of carbonaceous materials and the pyrolyzing temperature of biochars. The reduction in HBCDs uptake by Eisenia fetida (an epigeic species) was greater than by Metaphire guillelmi (an anecic species). The 2 earthworm species both showed bioaccumulative selectivity on certain HBCD diastereoisomer and enantiomer in the amended soils, which was similar to that in the control soil. Moreover, Tenax-assisted HBCDs desorption test was carried out for the simulation of their bioavailability. The rapid desorption fraction (Frap), total desorption (15 d), and 24 h desorption all correlated well with the uptake of HBCDs in the earthworms, suggesting that the 24 h-desorption, due to its easy availability, can be a good proxy to predict the bioavailability of HBCDs to earthworms in soil.

土壤有机污染物的吸附–生物降解耦合模型研究进展

污染物的微生物可利用性是控制其环境归趋的主要因素之一，也是决定受污染土壤的微生物修复技术成败的关键。有机污染物进入土壤后发生吸附作用，进而影响其生物可利用性。正确预测有机污染物在土壤环境中的微生物可利用性，需要建立可靠的吸附–降解动力学模型。本文介绍了五种国内外常用的有关农药和多环芳烃在土壤/沉积物上的吸附–降解耦合模型，综述了模型建立过程、评价方法、适用范围，探讨了现有模型在实际应用中的共性问题，以期为土壤污染的控制和修复提供思路。 Bioavailability of pollutants in soil is one of the main factors that determine their environmental fate. It is a key to the successful implementation of bioremediation of polluted soil. Sorption of organic pollutants occurs once they enter soil, and subsequently influence the bioavailability of the pollutants. To accurately predict the bioavailability of organic pollutants in soil, coupled sorption-biodegradation models need to be established. This paper introduces five coupled sorption-biodegradation models used in the literature to account for the bioavailability of pesticides and polycyclic aromatic hydrocarbons in soil and sediment as influenced by sorption. The overall objective of this paper is to offer proper ideas for soil pollution control and remediation. This is achieved by summarizing the establishment of these models, their evaluations and applications, and by discussing potential problems associated with these models.

Phytotoxicity of Citric Acid and Tween® 80 for Potential Use as Soil Amendments in Enhanced Phytoremediation

Enhanced phytoremediation adding biodegradable amendments like low molecular weight organic acids and surfactants is an interesting area of current research to overcome the limitation that represents low bioavailability of pollutants in soils. However, prior to their use in assisted phytoremediation, it is necessary to test if amendments per se exert any toxic effect to plants and to optimize their application mode. In this context, the present study assessed the effects of citric acid and Tween® 80 (polyethylene glycol sorbitan monooleate) on the development of alfalfa (Medicago sativa) plants, as influenced by their concentration and frequency of application, in order to evaluate the feasibility for their future use in enhanced phytoremediation of multi-contaminated soils. The results showed that citric acid negatively affected plant germination, while it did not have any significant effect on biomass or chlorophyll content. In turn, Tween® 80 did not affect plant germination and showed a trend to increase biomass, as well as it did not have any significant effect on chlorophyll levels. M. sativa appeared to tolerate citric acid and Tween® 80 at the tested concentrations, applied weekly. Consequently, citric acid and Tween® 80 could potentially be utilized to assist phytoremediation of contaminated soils vegetated with M. sativa.

Oral sealing using glue: a new method to distinguish between intestinal and dermal uptake of metals in earthworms

Earthworms may take up chemicals from soil and pore water, both through their skin (dermal) and by ingestion (oral). It remains unclear, however, what the relative importance of these pathways is. To assess bioavailability of pollutants in soil to earthworms, it is necessary that the contribution of each pathway is known. Lumbricus rubellus were sealed by means of medical histoacryl glue, to block ingestion of soil particles and pore water. For 6 d, these earthworms showed good survival and vitality and no soil ingestion was found. Equal metal uptake was found by sealed and unsealed earthworms exposed to an inert sand matrix continuously flushed with contaminated water. Therefore, pore water uptake via ingestion contributes little to metal accumulation. Uptake rates of Cd, Cu and Pb in sealed and unsealed earthworms exposed to two contaminated field soils were similar. Uptake and elimination kinetics of Zn were significantly lower in sealed earthworms exposed to one of the two field soils. Body concentrations of Cu and Pb could be completely attributed to the dermal route. For internal Cd and Zn concentrations, however, 0–17 and 21–30%, respectively, were derived from ingestion. It is concluded that for metals the dermal route is the uptake route of importance. The sealing method described here may be useful in a variety of earthworm nutrition and contamination-effect studies.

Concentration‐dependent kinetics of pollutant desorption from soils

Sorption-desorption kinetics play a major role in transport and bioavailability of pollutants in soils. Contaminant concentration is a potentially important factor controlling kinetics. A previous paper dealt with the effect of solute concentration on fractional uptake rates of phenanthrene and pyrene from a finite aqueous source. In this study we determined the effect of initial phenanthrene sorbed concentration (q(0)) on the fractional mass desorption rates from each of six soils to a zero-concentration solution, approximated by including a polymer adsorbent (Tenax) as a third-phase sink. The soils were preequilibrated with phenanthrene for 180 d. Consistent with theory, the fractional desorption rates determined by empirical curve fitting increased with q(0) provided the isotherm was nonlinear. After 500 to 600 d of desorption at the steepest possible concentration gradient, all soils retained a highly resistant fraction, which ranged from 4 to 31% of q(0), except for one soil at a high q(0). The highly resistant fraction decreased with increasing q(0), for nonlinear isotherm cases, but increased with q(0) for linear or nearly linear isotherm cases. Application of a nonlinear diffusion model, the dual-mode diffusion model (DMDM), to the nonresistant fraction gave reasonably good fits. The DMDM attributes the increase with concentration of the apparent diffusivity to a decrease in the proportion of sorbate occupying immobile sites (holes) in soil organic matter. The concentration-dependent term in the expression for the apparent diffusivity correlated with either of two indices that reflect the linearity of the sorption isotherm. Bunker C oil present in one soil acted as a partition domain. The findings of this study are consistent with heterogeneous models of soil organic matter, and indicate that concentration effects should be taken into account whenever desorption rate is important.