Reduction effects of solar radiation, mechanical tension, and soil burial on phthalate esters concentrations in plastic film and soils

Phthalate ester (PAEs) accumulation in wheat tissues and dynamic changes of rhizosphere microorganisms in the field with plastic-film residue

Phthalates acid esters (PAEs) have accumulated in soil and crops like wheat as a result of the widespread usage of plastic films. It is yet unclear, nevertheless, how these dynamic variations in PAE accumulation in wheat tissues relate to rhizosphere bacteria in the field. In this work, a field root-bag experiment was conducted to examine the changes of PAEs accumulation in the rhizosphere soil and wheat tissues under film residue conditions at four different growth stages of wheat, and to clarify the roles played by the microbial community in the alterations. Results showed that the plastic film residues significantly increased the concentrations of PAEs in soils, wheat roots, straw and grains. The maximum ΣPAEs concentration in soils and different wheat tissues appeared at the maturity, with the ΣPAEs concentration of 1.57 mg kg-1, 4.77 mg kg-1, 5.21 mg kg-1, 1.81 mg kg-1 for rhizosphere soils, wheat roots, straw and grains, respectively. The plastic film residues significantly changed the functions and components of the bacterial community, increased the stochastic processes of the bacterial community assembly, and reduced the complexity and stability of the bacterial network. In addition, the present study identified some bacteria associated with plastic film residues and PAEs degradation in key-stone taxa, and their relative abundances were positive related to the ΣPAEs concentration in soils. The PAEs content and key-stone taxa in rhizosphere soil play a crucial role in the formation of rhizosphere soil bacterial communities. This field study provides valuable information for better understanding the role of microorganisms in the complex system consisting of film residue, soil and crops.

Effect of aging on the release of di-(2-ethylhexyl) phthalate from biodegradable and petroleum-based microplastics into soil

Due to microplastics (MPs) being widely distributed in soil, the use of advanced oxidation to remediate organic-contaminated soils may accelerate the aging of MPs in soil and impact the release of di-(2-ethylhexyl) phthalate (DEHP), a potential carcinogen used as a plasticizer in plastics, from MPs. In this study, persulfate oxidation (PO) and temperature treatment (TT) were used to treat biodegradable and petroleum-based MPs, including polylactic acid (PLA), polyvinyl chloride (PVC), and polystyrene (PS). The methods used for evaluating the characteristics changes of MP were X-ray diffraction (XRD) analysis and water contact angle measurement. The effects of aging on DEHP release from MPs were investigated via soil incubation. The results showed PO and TT led to increased surface roughness, oxygen-containing functional group content, and hydrophilicity of the MPs with prolonged aging, consequently accelerating the release of DEHP from the MPs. Interestingly, PLA aged faster than PVC and PS under similar conditions. After 30 days of PO treatment, DEHP release from PLA into the soil increased 0.789-fold, exceeding the increase from PVC (0.454-fold) and PS (0.287-fold). This suggests that aged PLA poses a higher ecological risk than aged PVC or PS. Furthermore, PO treatment resulted in the oxidation and degradation of DEHP on the MP surface. After 30 days of PO treatment, the DEHP content in PLA, PVC, and PS decreased by 19.1%, 25.8%, and 23.5%, respectively. Specifying the types of MPs studied and the environmental conditions would provide a more precise context for the results. These findings provide novel insights into the fate of biodegradable and petroleum-based MPs and the potential ecotoxicity arising from advanced oxidation remediation in contaminated soils.

Exposure risk assessment of representative phthalate acid esters and associated plastic debris under the agricultural land use in typical Chinese regions

Phthalate acid esters (PAEs) are frequently detected in the global environment and can cause potential health hazards. In this study, quantitative exposure risk assessment was undertaken to derive soil generic assessment criteria (GAC) for six representative PAEs under the agricultural land use in the evaluated Chinese regions, which coupled multi-media transport and human exposure models based on multiple exposure pathways including vegetables consumption, dermal absorption, ingestion of soil and dust, and the exposure from non-soil sources. It is identified that the PAEs in agricultural soil are dominated by DEHP and DnBP representing 72-96% of the total PAEs. The GAC for BBP and DEHP, calculated on the basis of region-specific exposure parameters and soil properties in various locations, are stringent, signifying greater potential health risks from exposure to them, warranting more rigorous contamination management. The proposed soil GAC for plastic debris are 100, 107, 73 and 88 mg kg-1 for Heilongjiang Province, Beijing City, Jiangsu and Guangdong Provinces respectively. Additionally, the potential risks of 1.68 × 10-6 and 7 × 10-6 are identified for BBP and DEHP in Guangdong Province as indicated by the exceedance of target risk level of 1 × 10-6, with the consumption of vegetables being the dominant contributor to the total estimated PAEs exposure. Overall, this methodology based on the coupled contaminant transport and exposure models incorporating region-specific data provides a technical framework to derive science-based soil GAC for representative PAEs for maintaining and assessing soil quality and food safety under the agricultural land use.

Effect of particle size and environmental conditions on the release of di(2-ethylhexyl) phthalate from microplastics

The extensive use and improper handling of plastics have caused extensive microplastic (MP) pollution in terrestrial environments. Di(2-ethylhexyl) phthalate (DEHP), the main additive used in plastics, is toxic to organisms and may pose risks to human and animal reproductive functions. However, research on the release behavior of DEHP from MPs is scarce. In this study, the effects of particle size and environmental conditions (temperature, pH, ionic strength, and cation type) on DEHP release from polylactide (PLA), polystyrene (PS), and polyvinyl chloride (PVC) MPs were determined by performing leaching experiments. The results showed that when particle size decreased, the content of DEHP in the MPs and the amount of released DEHP increased though increasing specific surface area. An increase in temperature also promoted DEHP release; when the temperature increased from 15 °C to 45 °C, the amount of DEHP released from PLA, PS, and PVC increased by 38.4%, 71.0%, and 109%, respectively. The lower the crystallinity, the greater the increase in the amount of DEHP released. Ionic strength inhibited the release of DEHP from MPs. When Na+ concentration increased from 0 to 200 mM, the amount of DEHP released from PLA, PS, and PVC decreased by 27.4%, 41.6%, and 35.3%, respectively. The effect of Ca2+ on DEHP release from MPs was greater than that of Na+. In addition, the process of DEHP release from MPs fit well with a pseudo-first-order kinetic model. The results of this study provide a theoretical basis for managing and controlling the risks associated with plastic wastes.

Synthetic bacterial consortia enhanced the degradation of mixed priority phthalate ester pollutants

Dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butyl benzyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP), and di-n-octyl phthalate (DOP) are hazardous chemicals listed as priority pollutants that disrupt endocrine systems. According to available reports, these six priority phthalate esters (PAEs) are considered the most polluting; however, no studies have been conducted on the efficient remediation of these PAEs. We therefore designed and constructed a synthetic bacterial consortium capable of the simultaneous and efficient degradation of six priority PAEs in minimal inorganic salt medium (MSM) and soil. The consortium comprised Glutamicibacter sp. ZJUTW, which demonstrates priority for degrading short-chain PAEs; Cupriavidus sp. LH1, which degrades phthalic acid (PA) and protocatechuic acid (PCA), intermediates of the PAE biodegradation process; and Gordonia sp. GZ-YC7, which efficiently degrades long-chain priority PAEs, including DEHP and DOP. In MSM containing the six mixed PAEs (250 mg/L each), the ZJUTW + YC + LH1 consortium completely degraded the four short-chain PAEs within 48 h, and DEHP (100%) and DOP (62.5%) within 72 h. In soil containing the six mixed PAEs (DMP, DEP, BBP, and DOP, 400 mg/kg each; DBP and DEHP, 500 mg/kg, each), the ZJUTW + YC + LH1 consortium completely degraded DMP, DEP, BBP, and DBP within 6 days, and 70.84% of DEHP and 66.24% of DOP within 2 weeks. The consortium efficiently degraded the six mixed PAEs in both MSM and soil. We thus believe that this synthetic microbial consortium is a strong candidate for the bioremediation of environments contaminated with mixed PAE pollutants.

Residual status and source analysis of phthalate esters in Ulungur Lake, China

Ulungur Lake is the largest lake in northern Xinjiang and undertakes important aquatic tasks. It is the No. 1 fishing ground in northern Xinjiang, and the problem of persistent organic pollution in the water has received much attention. However, there are few studies on phthalate esters (PAEs) in the water of Ulungur Lake. Understanding the pollution levels, distribution characteristics and sources of PAEs is of great significance for the protection and prevention of water. Fifteen sampling sites are established in Ulungur Lake to collect water samples during flood and dry periods, then seventeen PAEs are extracted from the water samples and purified by liquid-liquid extraction-solid-phase purification. Gas chromatography-mass spectrometry is used to detect the pollution levels and distribution characteristics of the 17 PAEs and analyse their sources. Results show that the concentrations of PAEs in the dry and flood periods are 0.451-9.97 µg/L and 0.0490-6.38 µg/L, respectively. The concentration of ∑PAEs with time is characterised by the dry period > the flood period. The change in flow is the main reason for the diverse concentration distributions of PAEs in different periods. The concentration of ΣPAEs in the dry period is much lower on the side near the lake entrance of the Ulungur River and Irtysh River. In the dry period, PAEs mainly come from chemical production and the use of cosmetics and personal care products; in the flood period, they mainly come from chemical production. River input and atmospheric sedimentation are the main sources of PAEs in the lake.

Content level and risk assessment of phthalate esters in surface water of Bosten Lake, China

Bosten Lake is the main fishing and grazing area in Xinjiang. The pollution of phthalate esters (PAEs) in water has attracted much attention, but limited research has been conducted on PAEs in Bosten Lake. The distribution of PAEs in fifteen sampling sites of surface water in the dry and flood seasons were investigated to explore the content level of PAEs in Bosten Lake, and the risk was evaluated. Seventeen PAEs were detected by GC-MS after liquid-liquid and solid-phase purification. Results showed that the content of ∑PAEs in the water during dry and flood seasons is ND-26.226 μg/L and ND-7.179 μg/L. The content of PAEs in the water of Bosten Lake is at a medium level. DBP and DIBP are the main PAEs. The content of PAEs is related to the physicochemical properties of water, and the physicochemical properties of water in dry season have a more serious impact on PAEs. PAEs in water mainly come from domestic pollution and chemical production. The results of health risk assessment indicate that PAEs in water do not pose a carcinogenic risk or a non carcinogenic risk to human, which can meet the conditions of Bosten Lake as a fishing ground and livestock base, but the pollution of PAEs cannot be ignored.

The content of PAEs in field soils caused by the residual film has a periodical peak

The wide use of plastic film mulch has led to the release of phthalate esters (PAEs), which seriously threatens the soil environment and the safety of crop production. However, it is unknown whether there is a maximum threshold of soil PAEs accumulation induced by plastic film residue, and the dynamic changes of soil PAEs under field conditions are still unclear. To address these issues, a field experiment was conducted to investigate the temporal fluctuations of soil PAEs content and the response of microbial community structure in the field with plastic film residue. Results showed that the content of soil PAEs fluctuated during an observation period of one year, had a periodical peak in winter and summer, and was exacerbated by the increase in the aging degree and residual amount of plastic films. The PAEs content in soil with black films was higher than the US soil allowable criteria. High-throughput sequencing analysis showed that the addition of residual film significantly increased the alpha diversity of bacterial communities, changed the structure of bacterial community, and generated significant disturbances in bacterial function. Besides, the residual film recruited more microbiota related to plastic film and PAEs degradation. Results of the present study provide insight into the dynamic variation of soil PAEs caused by plastic film residue in one year, which is important to help evaluate the pollution risk of PAEs on soils and crops caused by residual plastic film.

Occurrence, source, ecological risk, and mitigation of phthalates (PAEs) in agricultural soils and the environment: A review

The widespread distribution of phthalates (PAEs) in agricultural soils is increasing drastically; however, the environmental occurrence and potential risk of PAEs in agricultural systems remain largely unreviewed. In this study, the occurrence, sources, ecotoxicity, exposure risks, and control measures of PAEs contaminants in agricultural soils are summarized, and it is concluded that PAEs have been widely detected and persist in the soil at concentrations ranging from a few μg/kg to tens of mg/kg, with spatial and vertical variations in China. Agrochemicals and atmospheric deposition have largely contributed to the elevated contamination status of PAEs in soils. In addition, PAEs cause multi-level hazards to soil organisms (survival, oxidative damage, genetic and molecular levels, etc.) and further disrupt the normal ecological functions of soil. The health hazards of PAEs to humans are mainly generated through dietary and non-dietary pathways, and children may be at a higher risk of exposure than adults. Improving the soil microenvironment and promoting biochemical reactions and metabolic processes of PAEs are the main mechanisms for mitigating contamination. Based on these reviews, this study provides a valuable framework for determining future study objectives to reveal environmental risks and reduce the resistance control of PAEs in agricultural soils.

Effect of plastic film mulching and film residues on phthalate esters concentrations in soil and plants, and its risk assessment

The application of plastic film mulching can greatly improve dryland productivity, while the release of toxic phthalate esters (PAEs) from the plastic film has generated concern. This study investigated the effects of mulched plastic film and residual plastic film on the PAE concentrations in the soil-crop system and assessed the risks to people eating crop products. The PAEs concentration in the 0-25 cm soil layer of plastic mulched farmland was 0.45-0.81 mg/kg, while the average PAEs concentration of 0.37-0.73 mg/kg in non-mulched farmland decreased by 19%. The PAEs concentration in mulched soil reached the highest in July, being 0.80-0.84 mg/kg, while in the non-mulched soil, the PAEs also appeared and gradually decreased from May at 0.62-0.74 mg/kg to October, and the PAEs concentrations were almost the same in the mulched and non-mulched soils at the harvest time in October at 0.37-0.44 mg/kg. With the amounts of residual film in farmland increasing from 0 kg/ha to 2700 kg/ha (equivalent to the total amount of residual film after 60 years of continuous plastic film mulching), the PAEs concentrations were no significant changes, being 0.54-0.93 mg/kg. Maize (Zea mays L.) roots could absorb and accumulate PAEs, and the bio-concentration factor (BCF) was 1.6-2.3, and the average PAEs concentrations in stems, leaves, and grains were 79%-80% of those in roots at 0.77-1.47 mg/kg. For the ingestion of maize grains or potato (Solanum tuberosum L.) tubers grown in plastic film mulched farmland or farmland containing residual film of 450-2700 kg/ha, the hazard index (HI) were less than 1, the carcinogenic risks (CRs) were 2.5 × 10^-7-2.2 × 10^-6, and the estrogenic equivalences were 6.17-17.73 ng E₂/kg. This study provides important data for the risk management of PAEs in farmlands.