Evaluation of combined noxious effects of siduron and cadmium on the earthworm Eisenia fetida

Soil Cd increased the leaf litter Cd remains of Solanum nigrum and Solanum lycopersicum

Plant litter decomposition is a natural pathway of heavy metal cycling in soil ecosystems, but the dynamics of heavy metal release during litter decomposition are relatively poorly understood. The purpose of this study was to investigate the effects of species, soil fauna and soil Cd addition on litter decomposition and Cd release dynamics. Therefore, we selected two plants, Solanum nigrum and S. lycopersicum with large differences in Cd accumulation capacity. First, they were enriched with Cd during the growing period and leaf litter was harvested after 6 months of pretreatment. Then, the decomposition of leaf litter was conducted with or without soil Cd and Eisenia fetida through lab pot tests. Our results showed that leaf litter Cd led to a significant decrease in litter decomposition rate (K value), with a maximum decrease of 32.1% in S. nigrum and 30.1% in S. lycopersicum. We observed that the presence of E. fetida significantly increased K value, but the effect was similar in the +leaf Cd treatment and the -leaf Cd treatment, both for S. nigrum and S. lycopersicum. Interestingly, the litter Cd concentration did not decrease during decomposition, but showed an increasing trend, especially for S. nigrum in the +soil Cd treatment. Moreover, the litter Cd remains was higher in the +soil Cd treatment compared to the -soil Cd treatment for both S. nigrum and S. lycopersicum, no matter whether with or without E. fetida. This result suggests that the Cd may be transferred from soil to litter, thus increasing the litter Cd remains. Overall, our study shows that leaf litter Cd slowed down the carbon cycling in ecosystems. In addition, the release of litter Cd has a lag, and the litter has a certain adsorption capacity for soil Cd, which intensifies the harm to the ecology during litter transfer.

Unraveling the complexities of Cd-aniline composite pollution: Insights from standalone and joint toxicity assessments in a bacterial community

Cadmium (Cd) and aniline frequently co-occur in industrial settings but have rarely been addressed as composite toxicants in terms of the overall toxicity despite extensive knowledge of the environmental impact of each individual pollutant. In this study, we attempt to assess the relation of individual and combined toxic effects of Cd and aniline using a bacterial consortium cultured from soils as a model system. Results showed that the consortial bacteria exhibited drastically stronger tolerance to stand-alone Cd and aniline in comparison to literature data acquired from single species studies. When occurring simultaneously, the joint toxicity displayed a concentration-dependent behavior that wasn't anticipated based on individual chemical tests. Specifically, additive effects manifested with Cd and aniline at their IC10s, but changed to synergistic when the concentrations increased to IC20, and finally transitioned into antagonistic at IC30s and beyond. In addition, co-occurring aniline appeared to have retarded the cellular accumulation of Cd while increasing the enzymatic activities of superoxide dismutase and catalase relative to that in Cd-alone treatments. Finally, the bacterial community experienced distinct compositional changes under solo and combined toxicities with several genera exhibiting inconsistent behavior between treatments of single and composite toxicants. Findings from this study highlight the complexity of bacterial response to composite pollutions and point to the need for more comprehensive references in risk and toxicology assessment at multi-chemical contamination sites.

Oxidative stress, growth inhibition, and DNA damage in earthworms induced by the combined pollution of typical neonicotinoid insecticides and heavy metals

Heavy metals pollution of soil and widespread application of neonicotinoid insecticides have caused environmental problems worldwide. To evaluate ecological toxicity resulting from the combined pollution of neonicotinoids and heavy metals, typical representatives of neonicotinoid insecticides (imidacloprid, thiamethoxam, dinotefuran) and heavy metals (cadmium, copper, zinc) were selected as soil pollutants; earthworms were used as test organisms. Analysis of the main and interaction effects of a combined pollution process were performed using a uniform design method. Results showed that the reactive oxygen species (ROS) content of earthworms in most treatment groups was higher during exposure than that of the control group. The malondialdehyde (MDA) and ROS content of earthworms demonstrated relatively low values on the 21st day and increased by the 28th day. The interaction between dinotefuran and Cd had significant antagonistic effects on ROS and MDA. The combined pollution adversely affected both the growth and genes of earthworms and also caused damage to the epidermis, midgut, and DNA. The interaction between imidacloprid and Cd was synergistic to ROS, weight inhibition rate, and Olive tail moment (OTM), but was antagonistic to MDA. Of all the single and combined exposures, Zn as a single chemical affected ROS and DNA damage the most, and MDA was significantly enhanced by imidacloprid. Composite pollutants may create different primary effects and interactions causing potential harm to soil organisms.

Cadmium pollution alters earthworm activity and thus leaf-litter decomposition and soil properties

It has been reported that heavy metal contamination can affect litter decomposition and soil properties through its impact on microbial communities. However, it is still unclear whether the expected changes in earthworm activities in responses to heavy metal contamination could affect these properties. Therefore, we quantified earthworm (Eisenia fetida) responses in survival rate to lethal cadmium (Cd) concentrations (0, 50, 100, 150, 200, 250, and 300 mg L^-1), and in burrowing ability, physiological characteristics, and feeding rate (on poplar leaf litter) to sub-lethal Cd concentrations (0, 15, 30, and 45 mg kg^-1). Finally, sub-lethal influences of Cd on the decomposition rate of poplar leaf litter and on soil properties were investigated in the present of E. fetida. The 12-, 24-, 36-, and 48-h LC₅₀ of Cd for E. fetida were 276.0, 208.6, 192.6, 179.8 mg L^-1, respectively. With increasing Cd concentration, malondialdehyde was stimulated, superoxide dismutase first increased and then decreased, while feeding rate, total borrowing length, and maximum burrowing depth consistently decreased. Consequently, leaf-litter decomposition rate and soil nutrient concentrations generally decreased with increasing Cd concentration. Our results indicate that, by affecting earthworm activities, Cd inhibited leaf-litter decomposition and led to the degradation of soil fertility. This study highlights the importance of earthworms in mediating soil functions under heavy metal stress.

Evaluation of joint toxicity of heavy metals and herbicide mixtures in soils to earthworms (Eisenia fetida)

It is widely acknowledged that a simplified and robust approach to evaluating thecombined effects of chemical mixtures is critical for ecological risk assessment (ERA) of contaminated soil. The earthworm (Eisenia fetida) was used as a model to study the combined effects of polymetallic contamination and the herbicide siduron in field soil using a microcosm experiment. The responses of multiple biomarkers, including the activities of catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR) and acetylcholine esterase (AChE), the concentrations of glycogen, soluble protein (SP), malonaldehyde (MDA), and metallothionein (MT), and the neutral red uptake test (NRU), were investigated. Multivariate analysis, Principal Component Analysis (PCA) and Spearman's Rank Correlations analysis (BVSTEP) revealed that the activities of AChE and CAT and the NRU content were the prognostic biomarkers capturing the minimum data set of all the variables. Internal Cd (tissue Cd) in earthworms was closely related to the health status of worms under combined contamination of heavy metals and siduron. The integrated effect (E_mix) calculated based on the activities of AChE and CAT and NRU content using the stress index method had significantly linear regression with internal Cd (p<0.01). E_mix(10), E_mix(20), and E_mix(50) were then calculated, at 1.27, 1.63 and 2.71 mg/kg dry weight, respectively. It could be concluded that a bioassay-based approach incorporating multivariate analysis and internal dose was pragmatic and applicable to evaluating combined effects of chemical mixtures in soils under the guidance of the top-down evaluation concept of combined toxicity.

An analysis of the versatility and effectiveness of composts for sequestering heavy metal ions, dyes and xenobiotics from soils and aqueous milieus

The persistence and bioaccumulation of environmental pollutants in water bodies, soils and living tissues remain alarmingly related to environmental protection and ecosystem restoration. Adsorption-based techniques appear highly competent in sequestering several environmental pollutants. In this review, the recent research findings reported on the assessments of composts and compost-amended soils as adsorbents of heavy metal ions, dye molecules and xenobiotics have been appraised. This review demonstrates clearly the high adsorption capacities of composts for umpteen environmental pollutants at the lab-scale. The main inferences from this review are that utilization of composts for the removal of heavy metal ions, dye molecules and xenobiotics from aqueous environments and soils is particularly worthwhile and efficient at the laboratory scale, and the adsorption behaviors and effectiveness of compost-type adsorbents for agrochemicals (e.g. herbicides and insecticides) vary considerably because of variabilities in structure, topology, bond connectivity, distribution of functional groups and interactions of xenobiotics with the active humic substances in composts. Compost-based field-scale remediation of environmental pollutants is still sparse and arguably much challenging to implement if, furthermore, real-world soil and water contamination issues are to be addressed effectively. Hence, significant research and process development efforts should be promptly geared and intensified in this direction by extrapolating the lab-scale findings in a cost-effective manner.

Effects of single and combined exposure to nano and bulk zinc-oxide and propiconazole on Enchytraeus albidus

Organisms in soil are often exposed to different mixtures of contaminants. These contaminants may interact with each other and, consequently, may have a different effect on organisms than each of them alone. We wanted to investigate possible effects of ZnO mixtures in bulk and nano form and fungicide propiconazole (PCZ) on biochemical parameters and reproduction in Enchytreus albidus. These compounds were applied separately and in binary mixture. In the single exposure experiment the EC₅₀ values for the number of juveniles were calculated: nano ZnO (641.21 ± 88.82 mg kg^-1), bulk ZnO (445.78 ± 148.4 mg kg^-1) and PCZ (3.63 ± 1.68 mg kg-1), respectively. These concentrations were subsequently used in the binary exposure experiment. Calculated combination indices (CI), that allow quantitative determination of chemical interactions at different concentration and effect level, indicated additive or antagonistic interactions (CI ≥ 1) of applied mixture ratios. The only ratio that showed synergistic interaction (CI < 1) was 75% EC₅₀ nZnO/25% EC₅₀ PCZ. Both ZnO forms caused acetylcholinesterase (AChE) activity increase of up to 40% of control level, as well as increased catalase (CAT) and glutathione S-transferase (GST) activities and malondialdehyde (MDA) level. PCZ did not affect AChE and CAT activities, yet it increased GST activity and MDA level. Induced levels of measured biomarkers indicate an oxidative stress after binary exposure, as well. These effects were not enhanced after binary exposure but reflected the effects on biomarkers that corresponding concentrations of these compounds generated in a single exposure experiment.

In-Situ Remediation of Cadmium and Atrazine Contaminated Acid Red Soil of South China Using Sepiolite and Biochar

The in-situ immobilization effect of sepiolite and biochar on the compound pollution of cadmium (Cd) and atrazine in acid red soil of south China was studied. Results showed that in a certain concentration range, sepiolite and biochar can improve the germination rate, ensure normal growth and increase biomass of pakchoi, reduce the content of Cd in edible parts of pakchoi in different degrees and meet international standards, and restrain absorption of atrazine in pakchoi completely. Sepiolite was more effective than biochar for the immobilization of Cd, while biochar was more effective than sepiolite for the immobilization of atrazine. Combined application of sepiolite and biochar in soil contaminated by Cd and atrazine was better than individual applications of sepiolite or biochar. The remediation method applied in this research can effectively repair the acid red soil with combined pollution of Cd and atrazine in south China, while also providing ideas for in-situ remediation of farmland soil with combined pollution of pesticides and metals.

Characterization of adsorption and desorption of lawn herbicide siduron in heavy metal contaminated soils

Siduron is a widely used herbicide in urban lawn and has been frequently detected in urban and suburban surface water. However, characteristics of its environmental behavior in soil are seldom reported. The combined pollution of heavy metals, especially for Cu, Pb, Cd, Zn and siduron would be common because of the widely existence of heavy metal pollution in urban soils. In this study, four soils with similar physicochemical properties but different levels of preexisting heavy metals were selected to investigate the adsorption and successive desorption of siduron using batch experiments. The results revealed a low sorption of siduron to all the tested soils. The organic carbon normalized distribution coefficient (K_oc) of siduron in the studied soils ranged from 117 to 137 L kg^-1 and was not significantly correlated to heavy metal levels. No apparent desorption hysteresis was observed with the hysteresis index (HI) ranging from 0.921 to 1.11. More than 50% of the sorbed siduron was readily released into soil solution. Results suggested that siduron was highly mobile and bioavailable in the studied soils. Significant correlation was found between adsorption/desorption parameters and soil organic carbon (SOC) in four soils. soil organic matter was thus considered as the dominant factor determining the adsorption and desorption of siduron in soils. Different from most of reported studies conducted by laboratory-amended soils, the influence of preexisting heavy metals on the adsorption-desorption of siduron was not significant in this work.

Ecological risk evaluation of combined pollution of herbicide siduron and heavy metals in soils

Combined pollution of agrichemicals and heavy metals in urban lawn soils were commonly observed throughout the world, and the co-existed two chemicals could interact with each other both in environment behavior and toxic effect. However, little has been reported on the ecological risk of their combined pollution, especially in field due to lack of systematic methodology. In this study, four soils (C, N1, N2, N3) from two public parks in Beijing, China, with similar properties but contrasting heavy metal contaminated level were chosen to assess the ecological risks of co-existed herbicide siduron and heavy metals. Environmental behaviors of siduron in studied soils were investigated with batch experiments in lab, based on which the environmental exposure level of siduron was simulated with HYDRUS-1D. Results suggested that soil organic matter (SOM) rather than the co-existed heavy metals was the dominant factor affecting the fate and the accumulation of siduron in soils. Soil N2 with the highest SOM, showed the strongest tendency to retain siduron among the studied soils. Significant joint effect of siduron and heavy metals on cucumber root elongation was observed through lab experiments. Thus, the joint toxicity of siduron and heavy metals were calculated based on single toxicology data of them using independent action (IA) and concentration addition (CA) model. Then, the predicted no effect concentration (PNEC_soil) of siduron was calculated with equilibrium partitioning method and extrapolation techniques. The PNEC_soil of siduron was the lowest in heaviest heavy metal contaminated soil N3. The risk characterization ratios (RCR) of siduron in four soils were all >1. The highest RCR of siduron in soil N3 suggested that it was the joint toxicity of siduron and heavy metals to organisms determining the ecological risks of siduron in combined polluted soils.

Ecotoxicological effects of binary mixtures of siduron and Cd on mRNA expression in the earthworm Eisenia fetida

This study aimed to investigate the eco-toxicological responses of earthworm (Eisenia fetida) exposed to combined siduron (herbicide) and cadmium (Cd). Eisenia fetida gene expressions including metallothionein (MT) and heat shock protein70 (Hsp70) were analyzed using real-time Polymerase Chain Reaction after individual and combined siduron (0.90, 1.80, 3.60 and 7.20μgcm^-2) and Cd (0.225, 0.45, 0.90 and 1.80μgcm^-2) sublethal exposures. Where, the nature of the toxicological interactions between siduron and Cd in inducing or suppressing MT and Hsp70 expression was determined by applying the Combination index (CI)-isobologram model. The results revealed significant variations in MT and weak changes in Hsp70 expression when the earthworms were exposed to individual Cd. The individual siduron exposure exhibited a significant down-regulation (p<0.01) in MT during all treatments and in Hsp70 expression only at 7.20μgcm^-2 concentration; while the mixtures of siduron and Cd exposures resulted a significant down regulation (p<0.05) in both MT and Hsp70 expressions. Moreover, the combined siduron and Cd exposure revealed nearly additive effect (CI=1) at the lower effect levels and significant synergistic effect (CI<1) at the higher effect levels for both MT and Hsp70 expression. The synergistic effects of combined siduron and Cd suggest that there might be a potential risk connected to the co-occurrence of these chemicals in the environment.

The eco-toxic effects of pesticide and heavy metal mixtures towards earthworms in soil

Earthworms are the key soil organisms, contribute to many positive ecological services that could be degraded by pesticides and other soil pollutants such as heavy metals. Chemicals usually occur as mixtures in the environmental systems which can lead synergistic effects. The assessment and characterization of soil pollutants that effects risks are very difficult due to the complexity of soil matrix, poor understanding about the fate and effects of chemical combinations like pesticide and metal mixtures in terrestrial systems, and scarcity of toxicological data on mixtures of pollutants. In this review we summarized the current studies on individual and joint effects of pesticides and metals on earthworms and indicate the mixture that cause the synergistic interactions. The review explores the methods and models used previously to evaluate the toxicity of chemical mixtures, and suggests the perspective approaches for a better knowledge of combine effects as well as research methods The summarized report indicates that pesticide and metal mixtures at all organization levels affect the earthworms negatively. Whereas, the combined pollution generated by mixtures of pesticides and metal ions could induce the DNA damage, disruption in enzyme activities, reduction in individual survival, production and growth rate, change in individual behavior such as feeding rate, and decrease in the total earthworm community biomass and density. Among the pesticides organophosphates were identified the most toxic pesticides causing the synergistic effects. The findings indicate the scarcity of toxicological data concerning the assessment of pesticide and metal mixtures at genome level; while the mechanisms causing synergism were still not sufficiently explored.