Estimating the toxicity of the weak base carbendazim to the earthworm (Eisenia fetida) using in situ pore water concentrations in different soils

The influence of soil organic matter content and substance lipophilicity on the toxicity of pesticides to the earthworm Eisenia andrei

To account for potential differences in bioavailability (and toxicity) due to different soil organic matter (OM) contents in natural and artificial soil (AS), in the current European environmental risk assessment (ERA) a correction factor (CF) of 2 is applied to toxicity endpoints for so called lipophilic pesticides (i.e. log Kow > 2) generated from laboratory tests with soil invertebrates. However, the appropriateness of a single CF is questioned. To improve the accuracy of ERA, this study investigated the influence of soil OM content on the toxicity to the earthworm Eisenia andrei of five active substances used in pesticides covering a wide range of lipophilicity. Laboratory toxicity tests were performed in AS containing 10 %, 5 % and 2.5 % peat, and a natural LUFA 2.2 soil (4.5 % OM), assessing effects on survival, biomass change and reproduction. Pesticide toxicity differed significantly between soils. For all pesticides, toxicity values (LC50, EC50) strongly correlated with soil OM content in AS (r2 > 0.82), with toxicity decreasing with increasing OM content. Obtained regression equations were used to calculate the toxicity at OM contents of 10.0 % and 5.0 %. Model-estimated toxicity between these soils differed by factors of 1.9-3.6, and 2.1-3.2 for LC50 and EC50 values, respectively. No clear relationships between pesticide lipophilicity and toxicity-OM relationships were observed: the toxicity of non-lipophilic and lipophilic pesticides was influenced by OM content in a similar manner. The results suggest that the CF of 2 may not be appropriate as it is based on incorrect assumptions regarding the relationships between lipophilicity, OM content and toxicity. Further research should be conducted to understand the mechanistic link between toxicity and soil OM content to better define more chemically and ecologically appropriate CFs for ERA.

Bioavailability assessment of difenoconazole to earthworms (Eisenia fetida) in soil by oleic acid-embedded cellulose acetate membrane

Passive sampling technology is widely used to evaluate the bioavailability of pollutants. However, relatively few studies have used passive sampling membranes (PSMs) to evaluate the environmental risks of pollutants in soil, particularly pesticides. Here, the bioavailability of difenoconazole to earthworms (Eisenia fetida) was evaluated using an oleic acid-embedded cellulose acetate membrane (OECAM) for the first time. Difenoconazole reached 94 % equilibrium (T94%) within 1 d in OECAM. For soil pore water, the freely dissolved concentration (Cfree) of difenoconazole was determined using OECAM (R2 = 0.969). In the soil system, a strong linear correlation between the difenoconazole concentration in OECAM and earthworms was observed (R2 = 0.913). The bioavailability of difenoconazole was affected by the soil type and biochar content. The higher the content of soil organic matter and biochar, the lower the concentration of difenoconazole in earthworms, OECAM, and soil pore water. The concentrations of difenoconazole in pore water, earthworms, and OECAM decreased by 65.3, 42.0, and 41.6 %, respectively, when 0.5 % biochar was added. Difenoconazole mainly enters OECAM and earthworms through passive diffusion with similar uptake pathways. Therefore, the bioavailability of difenoconazole to earthworms in different soils can be evaluated using the OECAM.

Natural soils in OECD 222 testing - influence of soil water and soil properties on earthworm reproduction toxicity of carbendazim

Soil sorption properties can influence the bioavailability of substances and consequently the toxicity for soil organisms. Current standardised laboratory testing for the exposure assessment of pesticides to soil organisms uses OECD artificial soil that does not reflect the high variation in chemical-physical soil properties found in natural agroecosystems. According to guideline OECD 222, earthworm reproduction tests with Eisenia fetida and the pesticide carbendazim were performed in four natural soils and OECD artificial soil. By using pF 1.6, which ensures a uniformity in actual soil water availability, the control reproduction performance of E. fetida in all natural soils was at the same level as OECD artificial soil. In a principle component analysis, the variation in toxicity between the tested soils was attributable to a combination of two soil properties, namely total organic carbon content (TOC) and pH. The largest difference of 4.9-fold was found between the typical agricultural Luvisol with 1.03% TOC and pH 6.2 (EC₁₀: 0.17 (0.12-0.21) mg a.i. kg^-1 sdw, EC₅₀: 0.36 (0.31-0.40) mg a.i. kg^-1 sdw) and OECD artificial soil with 4.11% TOC and pH 5.6 (EC₁₀: 0.84 (0.72-0.92) mg a.i. kg^-1 sdw, EC₅₀: 1.07 (0.99-1.15) mg a.i. kg^-1 sdw). The use of typical agricultural soils in standardised laboratory earthworm testing was successfully established with using the measure pF for soil moisture adjustment. It provides a more application-oriented approach and could serve as a new tool to refine the environmental risk assessment at lower tier testing or in an intermediate tier based approach.

Insights into enhanced toxic effects by the binary mixture of carbendazim and procymidone on hepatic lipid metabolism in mice

Carbendazim (CBZ) and procymidone (PRO) are two widely used fungicides in agriculture. However, there are still gaps in knowledge regarding about the potential hazards of joint exposure to CBZ and PRO in animals. Here, 6-week-old ICR mice were exposed to CBZ, PRO and CBZ + PRO for 30 days, and metabolomics were performed to discover the mechanism by which the mixture enhanced the effects on lipid metabolism. Co-exposure to CBZ + PRO elevated the body weights, relative liver weights and relative epididymis fat weights, but not in the single exposure groups. Molecular docking analysis suggested that CBZ and PRO combined with peroxisome proliferator-activated receptor (PPARγ) at the same amino acid site as the agonist rosiglitazone. The RT-qPCR and WB results demonstrated that the levels of PPARγ were higher in the co-exposure group than in the single exposure groups. In addition, hundreds of differential metabolites were discovered by metabolomics and enriched in different pathways, such as pentose phosphate pathway and purine metabolism. A unique effect, a decrease in glucose-6-phosphate (G6P) that promoted more NADPH production, was observed in the CBZ + PRO group. These results demonstrated that exposure to CBZ + PRO caused more serious lipid metabolism disorder in the liver than exposure to a single fungicide, which could provide some new insight for the toxic effects after fungicides joint exposure.

Genotoxicity of organic contaminants in the soil: A review based on bibliometric analysis and methodological progress

Organic contaminants (OCs) are ubiquitous in the environment, posing severe threats to human health and ecological balance. In particular, OCs and their metabolites could interact with genetic materials to induce genotoxicity, which has attracted considerable attention. In this review, bibliometric analysis was executed to analyze the publications on the genotoxicity of OCs in soil from 1992 to 2021. The result indicated that significant contributions were made by China and the United States in this field and the research hotspots were biological risks, damage mechanisms, and testing methods. Based on this, in this review, we summarized the manifestations and influencing factors of genotoxicity of OCs to soil organisms, the main damage mechanisms, and the most commonly utilized testing methods. OCs can induce genotoxicity and the hierarchical response of soil organisms, which could be influenced by the physicochemical properties of OCs and the properties of soil. Specific mechanisms of genotoxicity can be classified into DNA damage, epigenetic toxicity, and chromosomal aberrations. OCs with different molecular weights lead to genetic material damage by inducing the generation of ROS or forming adducts with DNA, respectively. The micronucleus test and the comet test are the most commonly used testing methods. Moreover, this review also pointed out that future studies should focus on the relationships between bioaccessibilities and genotoxicities, transcriptional regulatory factors, and potential metabolites of OCs to elaborate on the biological risks and mechanisms of genotoxicity from an overall perspective.

Data-driven analysis on immobilized microalgae system: New upgrading trends for microalgal wastewater treatment

Microalgal immobilization is receiving increasing attention as one of the most viable alternatives for upgrading conventional wastewater treatment. However, an in-depth discussion of the state-of-the-art and limitations of available technologies is currently lacking. More importantly, the reason for the hesitant development of immobilized microalgae for wastewater treatment remains unclear, which hinders its practical application. Thus, comprehensively understanding and evaluating details on immobilized microalgae is urgently needed, especially for the current advances of immobilization of microalgae in wastewater treatment over the last few decades. In this review, scientometric approach is used to explore research hotspots and visualize emerging trends. Data-driven analysis is used to scientifically and methodically determine hotspots in the current research on immobilized microalgal wastewater treatment, along with that the implicit inner connection underlying the frequent co-occurring terms was explored in depth. Four hotspots focusing on immobilized microalgae for wastewater treatment were identified, mainly demonstrating: (1) main factors including light, temperature and immobilization methods would majorly affect the treatment performance of immobilized microalgae; (2) immobilized microalgae membrane bioreactor, immobilized microalgae-based microbial fuel cell and immobilized microalgae-based bed reactor are three dominant treatment systems; (3) immobilized microalgae have a higher robustness and tolerance for treating various types of wastewater; and (4) a complete sustainable circle from wastewater treatment to resource conversion via the immobilized microalgae can be achieved. Finally, several new directions and new perspectives that expose the necessity for fulfilling further research and fundamental gaps are pointed out. Taken together, this review provides helpful information to facilitate the development of innovative and feasible immobilized microalgal technologies thus increasing their viability and sustainability.

Estimating the bioavailability of acetochlor to wheat using in situ pore water and passive sampling

The intensive use of acetochlor in China leads to its extensive existence in soil which may result in contamination of crops and commodities. Therefore, it is vital to assess the bioavailability and phytotoxicity of acetochlor to crops. In this study, four measurements involved in in situ pore water extraction (C_IPW), passive sampling extraction (C_free), ex situ pore water extraction (C_EPW), and organic solvent extraction (C_soil) were conducted to assess the bioavailability and phytotoxicity of acetochlor to wheat plant plants in five soils. The results showed that the acetochlor concentrations accumulated in wheat foliage and roots were in the range of 0.11-0.87 mg/kg and 0.09-2.02 mg/kg in the five tested soils, respectively, and had a significant correlation with the acetochlor values analyzed by C_IPW (R² = 0.83-0.90, p < 0.0001) or the C_free method (R² = 0.86-0.92, p < 0.0001). The acetochlor concentrations in the five soils measured by these two methods were also correlated with the IC₅₀ values of acetochlor in wheat foliage and roots (R² > 0.69, p ≤ 0.05). The results indicated that the C_IPW and C_free methods were effective in evaluating acetochlor toxicity to wheat and the acetochlor concentrations in wheat. The effects of soil physical and chemical properties including pH, organic matter content (OMC), clay content, and cation exchange capacity (CEC) on the acetochlor toxicity to wheat were analyzed, and soil OMC was found to be the dominant factor affecting the toxicity of acetochlor in the soil-wheat system.

Carbendazim shapes microbiome and enhances resistome in the earthworm gut

BACKGROUND

It is worrisome that several pollutants can enhance the abundance of antibiotic resistance genes (ARGs) in the environment, including agricultural fungicides. As an important bioindicator for environmental risk assessment, earthworm is still a neglected focus that the effects of the fungicide carbendazim (CBD) residues on the gut microbiome and resistome are largely unknown. In this study, Eisenia fetida was selected to investigate the effects of CBD in the soil-earthworm systems using shotgun metagenomics and qPCR methods.

RESULTS

CBD could significantly perturb bacterial community and enrich specific bacteria mainly belonging to the phylum Actinobacteria. More importantly, CBD could serve as a co-selective agent to elevate the abundance and diversity of ARGs, particularly for some specific types (e.g., multidrug, glycopeptide, tetracycline, and rifamycin resistance genes) in the earthworm gut. Additionally, host tracking analysis suggested that ARGs were mainly carried in some genera of the phyla Actinobacteria and Proteobacteria. Meanwhile, the level of ARGs was positively relevant to the abundance of mobile genetic elements (MGEs) and some representative co-occurrence patterns of ARGs and MGEs (e.g., cmx-transposase and sul1-integrase) were further found on the metagenome-assembled contigs in the CBD treatments.

CONCLUSIONS

It can be concluded that the enhancement effect of CBD on the resistome in the earthworm gut may be attributed to its stress on the gut microbiome and facilitation on the ARGs dissemination mediated by MGEs, which may provide a novel insight into the neglected ecotoxicological risk of the widely used agrochemicals on the gut resistome of earthworm dwelling in soil. Video abstract.

The protective layer formed by soil particles on plastics decreases the toxicity of polystyrene microplastics to earthworms (Eisenia fetida)

The recent discovery of microplastics contaminants in most ecosystems has raised major health issues, yet knowledge on their impact on soil organisms is limited, especially their toxicity evolution with aging. Herein, the toxicity of polystyrene microplastic (PS-MP) to earthworm (Eisenia fetida) along with aging was investigated. Results showed that the 28 d-LC₅₀ (50% lethal concentration) of PS-MP was 25.67 g kg^-1, whereas that increased to 96.47 g kg^-1 after PS-MP initially aged in soil for 28 days, indicating the toxicity of PS-MP decreased with aging. Laser scanning confocal microscope and scanning electron microscope (SEM) found that the toxicity of PS-MP to earthworm may be due to the ingestion of PS-MP by earthworms and the physical damage (e.g., epidermis abrasion and setae loss) of PS-MP to earthworms. Similarly, the levels of reactive oxygen species, antioxidant enzyme activities and malondialdehyde content increased with PS-MP concentrations from 0.1 to 1.5 g kg^-1, but decreased with aging from 7 to 28 days. The integrated biomarker response index also confirmed that the toxicity of PS-MP decreased with aging. SEM found that PS-MP were progressively covered by soil particles during soil aging, inducing the formation of protective layer and increasing the particle size of PS-MP, which prevented direct contact with earthworms and decreased the ingestion of PS-MP, in turn decreased PS-MP toxicity. Overall, our study provides valuable insights for elucidating the effect of aging on the toxicity of microplastics.

Distinct uptake and accumulation profiles of triclosan in youdonger (Brassica campestris subsp. Chinensis var. communis) under two planting systems: Evidence from 14C tracing techniques

Triclosan is a widely used biocide against microorganisms and is ubiquitously distributed in the environment. Triclosan can be accumulated into plants from soil and hydroponic media. However, little information is currently available on the comparative fate of triclosan in plants under soil and hydroponics cultivation conditions and factors governing uptake. Therefore, this study was designed to comparatively elucidate the uptake mechanism of ¹⁴C-triclosan in youdonger (Brassica campestris subsp. Chinensis var. communis) grown under different soils and hydroponics and clarify dominant uptake factors. Results showed that 77.2% of ¹⁴C were accumulated in youdonger grown in a hydroponic system, while only 1.24%-2.33% were accumulated in the two soil-planting systems. In addition, the bioconcentration factor (BCF) of ¹⁴C-triclosan in soil-plant systems was approximately 400-fold smaller than that in the hydroponics. In the soil-planting system, a strong linear correlation was found between concentrations of triclosan in soil pore water and youdonger plant (R² > 0.85, p < 0.01) at different incubation times. Therefore, triclosan in pore water might be a good indicator to estimate its accumulation in plants and is significantly affected by soil pH, clay, and organic matter contents. The estimated average dietary intakes of triclosan for youdonger grown in hydroponic and soil-planting systems were estimated to be 1.31 ng day^-1 kg^-1 and 0.05-0.12 ng day^-1 kg^-1, respectively, much lower than the acceptable dietary intakes of triclosan (83 μg day^-1 kg^-1), indicating no significant human health risks from youdonger consumption. This study provided insights into uptake routes of triclosan into youdonger plants from both soil and hydroponic systems, bioavailability of triclosan in different soils, and further assessment of human exposure to triclosan from youdonger.

Accumulation of epoxiconazole from soil via oleic acid-embedded cellulose acetate membranes and bioavailability evaluation in earthworms (Eisenia fetida)

A passive sampler in the soil environment is a relatively novel technique and has had quite limited applications, especially for pesticides. Oleic acid-embedded cellulose acetate membranes (OECAMs) were developed to evaluate the bioavailability of epoxiconazole (EPO) to earthworms (Eisenia fetida). The uptake of EPO by OECAMs (R² = 0.975) and earthworms (R² = 0.938) was compared and found to follow a two-compartment kinetic model. EPO sampling by OECAMs reached equilibrium (94%) within 2 d. OECAM could be used to determine the concentration of EPO in soil porewater. Furthermore, a significant linear relationship (R² = 0.990) was observed between the EPO concentrations in earthworms and the OECAMs. The EPO concentrations in the porewater and OECAMs were lower in soils with a higher organic matter (OM) content. The EPO concentrations in the porewater, earthworms, and OECAMs decreased by 64.4, 49.0, and 56.1%, respectively, in the presence of 0.5% biochar, compared with the control. Furthermore, the use of OECAMs versus earthworms for soil testing also allows you to avoid factors that increase variance in organisms, such as avoidance behaviors or feeding. Therefore, OECAMs show good potential for use as a passive sampler to evaluate the bioavailability of EPO.

Bioavailability and toxicity of imazethapyr in maize plant estimated by four chemical extraction techniques in different soils

The bioavailability and toxicity of herbicides on the crop depend on its uptake efficiency from the soil, and thus the assessment of the bioavailable fraction of herbicides in soil is a crucial work. In this study, we investigated the uptake concentration and toxicity of imazethapyr in maize plant using four chemical measurements, including the extraction of in situ pore water (C_IPW), ex situ pore water (C_EPW), organic solvent (C_soil) and passive sampling (C_free) in five soils. The results obtained that the C_IPW in a specific soil had the most significant correlation with the uptake concentration of imazethapyr in maize plant (R² = 0.8851-0.9708), followed by C_EPW (R² = 0.8911-0.9565) and C_free (R² = 0.7881-0.9673). However, C_free showed a higher correlation when considering all five soils, and thus C_free can describe the bioavailability beyond the types of soil. Additionally, the median inhibition concentrations (IC₅₀) of imazethapyr to maize plant ranged from 5.0 to 6.9 mg/kg in five soils, and the C_IPW, C_EPW and C_free had better relationships with the IC₅₀ (R² > 0.8681) than the C_soil (R² = 0.6782). The effects of soil properties on the phytotoxicity of imazethapyr, including pH, organic matter content, cation exchange capacity and clay content, were studied, and the soil pH was shown to be a main factor. This study demonstrated that the freely dissolved fraction and soil pore water concentration of imazethapyr in soil can be used to evaluate its bioavailability and toxicity to maize.

Chemical factors affecting uptake and translocation of six pesticides in soil by maize (Zea mays L.)

Uptake of residual pesticides in a soil by a certain crop plant may be governed by their physicochemical properties. Uptake and translocation of pesticides (imidacloprid, acetamiprid, tricyclazole, azoxystrobin, tebuconazole and difenoconazole) with the octanol/water partition coefficient (log K_ow) ranging from 0.57 to 4.36 were investigated in soil with maize as a model plant. The results show that all tested pesticides in soil were uptaken by maize with accumulation amount of 27.73, 17.75, 18.96, 12.56, 10.66 and 2.13 μg for imidacloprid, acetamiprid, tricyclazole, azoxystrobin, tebuconazole and difenoconazole at 14 d, respectively. The accumulation amount was negatively correlated with adsorption coefficients and positively correlated with pesticide concentration in in situ pore water (C_IPW). Root bioconcentration factor varied widely from 0.61 for imidacloprid to 974.64 for difenoconazole was positively correlated with log K_ow and molecular weight but negatively with water solubility. Conversely, translocation factor varied from 0 for difenoconazole to 1.64 for imidacloprid was negatively correlated with log K_ow but positively with water solubility. It determined that uptake, accumulation and translocation of the pesticides in soil by maize are governed by their physicochemical properties, especially log K_ow. C_IPW is an appropriate candidate to evaluate the accumulation of pesticides in maize from soil.

Acute and chronic toxicity of the fungicide carbendazim to the earthworm Eisenia fetida under tropical versus temperate laboratory conditions

Research efforts into the potential side-effects of pesticides on beneficial organisms have focused on temperate test species and conditions. There is thus a need for studies into the ecotoxicity of a vaster range of pesticides under tropical conditions. The present study therefore aimed to compare the acute and chronic toxicity of the fungicide carbendazim to the earthworm Eisenia fetida under tropical and temperate conditions. To this end, laboratory toxicity tests were conducted with a tropical and European strain of E. fetida, using different artificial (OECD and TAS) and natural (LUFA and TNS) soils, and under different test temperatures (20 °C and 28 °C). In the acute lethality tests with artificial soils, the tropical strain of E. fetida was three to four order of magnitude less sensitive than the European strain, which is ascribed to the higher test temperature and (hence) higher microbial activity/pesticide degradation. The tropical strain was particularly sensitive in the tropical natural soil, which was attributed to the low pH (3.9) of this soil. The chronic toxicity tests overall also showed a lower sensitivity of the tropical strain on reproduction. These findings thus support the use of toxicity data generated under temperate conditions in tropical pesticide effect assessments. However, intensive agricultural practices in the tropics may dictate that exposure levels (and hence potentially also risks) are higher.

Biochar reduced Chinese chive (Allium tuberosum) uptake and dissipation of thiamethoxam in an agricultural soil

Information about the effect of biochar on the environmental fate of pesticide thiamethoxam (THI) in soil-vegetable ecosystems is limited. Therefore, the influence of a wood-derived biochar produced at 450 °C (BC450) on the uptake of THI by Chinese chive (Allium tuberosum) and its dissipation in soil was investigated using a 42-day pot experiment. BC450 addition decreased THI uptake and its metabolite clothianidin (CLO) by 22.8 % and 37.6 %, respectively. However, the half-life of THI in soil rose from 89.4-120 days, indicating that BC450 increased soil THI's persistence. The decreased bioavailability and increased persistence of THI resulted mainly from the higher sorption capacity of BC450 to THI and CLO, which, in turn, enhanced the soil sorption capacity. Consequently, the application of BC450 increased the soil microbial diversity and altered the structure of the microbial community. Although the abundance of Actinobacteria associated with the biodegradation of THI, increased the persistence of THI in the BC450-amended soil, mainly due to the decrease in bioavailable THI. Our findings provide valuable information about the effect of biochar on the fate of THI and its metabolites in agricultural soil and will help to guide the practical application of biochar to remediate soils contaminated with neonicotinoid pesticides.

Effect of Biochar on the Enantioselective Soil Dissipation and Lettuce Uptake and Translocation of the Chiral Pesticide Metalaxyl in Contaminated Soil

Enantioselectivity is usually ignored when assessing potential biochar-based methods of redressing pesticide contamination of soils. In this study, the effect of woodchip biochar (WBC) on the enantioselective dissipation of metalaxyl in soil and its uptake and translocation by lettuce were investigated. S-metalaxyl (T1/2 = 29.8 days) dissipated more quickly than R-metalaxyl (T1/2 = 36.4 days) in unamended soil. The addition of WBC to the soil decreased the dissipation rate and the enantioselectivity of metalaxyl. Metalaxyl distribution showed opposing enantioselectivity in lettuce, with roots and shoots showing preferences for R-metalaxyl and S-metalaxyl, respectively. Enrichment with WBC decreased the concentrations of metalaxyl and metalaxyl acid enantiomers in lettuce and reduced the ability of the shoots to transport the highly toxic R-metalaxyl from roots. This is the first study to provide evidence that amending soil with biochar affects the enantioselective uptake and translocation of a chiral pesticide.

Adsorption and Desorption of Carbendazim and Thiamethoxam in Five Different Agricultural Soils

The adsorption and desorption behaviors of carbendazim (CBD) and thiamethoxam (TMX) were systematically studied in five different agricultural soils. The adsorption and desorption isotherms of CBD and TMX in the five different soils were fitted well by the Freundlich model. The Freundlich adsorption coefficient (K_f^ads) and Freundlich desorption coefficient (K_f^des) of CBD in the five different soils were 1.46-19.53 and 1.81-3.33, respectively. The corresponding values of TMX were 1.19-4.03 and 2.07-6.45, respectively. The adsorption affinity and desorption ability of the five different soils for CBD and TMX depended mainly on soil organic matter content (OMC) and cation exchange capacity (CEC). Desorption hysteresis occurred in the desorption process of CBD and TMX in the five different agricultural soils, especially for TMX. It is concluded that the adsorption-desorption ability of CBD was much higher than that of TMX in the five different agricultural soils, which was attributed to soil OMC and CEC.

Mechanism of the effect of pH and biochar on the phytotoxicity of the weak acid herbicides imazethapyr and 2,4-D in soil to rice (Oryza sativa) and estimation by chemical methods

The existing form of an ionizable organic compound can simultaneously affect its soil adsorption and plant bioactivity. In this experiment, the adsorption and bioactivity of two weak acid herbicides (WAHs), imazethapyr and 2,4-D, were studied to explore the predominant mechanism by which the soil pH and the addition of biochar can influence the phytotoxicity of WAHs in soil. Then, the WAH concentration extracted by hollow fiber-based liquid-phase microextraction (C_HF-LPME), the in situ pore water concentration (C_IPW) and the added concentration (C_AC) were employed to estimate the phytotoxicity. The results showed that with increased pH from 5.5 to 8.5, the phytotoxicity of the WAHs to rice increased about 1-fold in the soil, but decreased in aqueous solutions, the IC₅₀ values for imazethapyr and 2,4-D at pH 5.0 were 3- and 2-fold higher than that at pH 8.0. In addition, the soil adsorption decreased, indicating that the adsorption process was the dominant factor for the variation of the phytotoxicity of the WAHs in the tested soil instead of the decreasing bioactivity. The concentration that inhibits plant growth by 50% (IC₅₀) calculated by the C_AC in different pH and biochar soils ranged from 0.619 to 3.826 mg/kg for imazethapyr and 1.871-72.83 mg/kg for 2,4-D. The coefficient of variation (CV) of the IC₅₀ values reached 65.61% for imazethapyr and 130.0% for 2,4-D. However, when IC₅₀ was calculated by C_IPW and C_HF-LPME, the CVs of the IC₅₀ values decreased to 23.51% and 36.23% for imazethapyr and 40.21% and 50.93% for 2,4-D, respectively. These results suggested that C_IPW and C_HF-LPME may be more appropriate than C_AC for estimating the phytotoxicity of WAHs.

Amelioration of acidic soil increases the toxicity of the weak base carbendazim to the earthworm Eisenia fetida

Ameliorating acidic soils is a common practice and may affect the bioavailability of an ionizable organic pollutant to organisms. The toxicity of the weak base carbendazim to the earthworm (Eisenia fetida) was studied in an acidic soil (pH-H₂O, 4.6) and in the ameliorated soil (pH-H₂O, 7.5). The results indicated that the median lethal concentration of carbendazim for E. fetida decreased from 21.8 mg/kg in acidic soil to 7.35 mg/kg in the ameliorated soil. To understand why the amelioration increased carbendazim toxicity to the earthworm, the authors measured the carbendazim concentrations in the soil porewater. The authors found increased carbendazim concentrations in porewater, resulting in increased toxicity of carbendazim to earthworms. The increased pore concentrations result from decreased adsorption because of the effects of pH and calcium ions.

Ecotoxicity of climbazole, a fungicide contained in antidandruff shampoo

Emerging pollutants such as personal care products can reach the environment via effluents from wastewater treatment plants (WWTPs) and digested sludge. Only recently, the antidandruff agent and antimycotic climbazole was detected for the first time in a WWTP effluent with concentrations up to 0.5 µg/L. Climbazole acts as a C14-demethylase inhibitor (DMI) fungicide and thus has a high efficacy against fungi, but knowledge of its potential environmental impact is lacking. Therefore, the aim of the present study was to characterize climbazole's ecotoxicity by conducting standard biotests with organisms representing different trophic levels from the aquatic as well as the terrestrial ecosystems. It was found that the toxicity of climbazole is mostly similar to that of other DMI fungicides, whereas it proved to be particularly toxic to primary producers. The lowest median effective concentrations (EC50s) were determined for Lemna minor, at 0.013 mg/L (biomass yield), and Avena sativa, at 18.5 mg/kg soil dry weight (shoot biomass). Reduction of frond size in water lentils and shoot length in higher plants suggested an additional plant growth-retarding mode of action of climbazole. In addition, it was demonstrated here that for an ionizable compound such as climbazole, the soil pH can have a considerable influence on phytotoxicity.