Toxic effects of pentachlorophenol and 2,2',4,4'-tetrabromodiphenyl ether on two generations of Folsomia candida

Ecological impacts and potential hazards of nickel on soil microbes, plants, and human health

Nickel (Ni) contamination poses a serious environmental concern, particularly in developing countries: where, anthropogenic activities significantly contributes to Ni accumulations in soils and waters. The contamination of agricultural soils with Ni, increases risks of its entry to terrestrial ecosystems and food production systems posing a threat to both food security and safety. We examined the existing published articles regarding the origin, source, accumulation, and transport of Ni in soil environments. Particularly, we reviewed the bioavailability and toxic effects of Ni to soil invertebrates and microbes, as well as its impact on soil-plant interactions including seed germination, nutrient uptake, photosynthesis, oxidative stress, antioxidant enzyme activity, and biomass production. Moreover, it underscores the potential health hazards associated with consuming crops cultivated in Ni-contaminated soils and elucidates the pathways through which Ni enters the food chain. The published literature suggests that chronic Ni exposure may have long-term implications for the food supply chain and the health of the public. Therefore, an aggressive effort is required for interdisciplinary collaboration for assessing and mitigating the ecological and health risks associated with Ni contamination. It also argues that these measures are necessary in light of the increasing level of Ni pollution in soil ecosystems and the potential impacts on public health and the environment.

Multigenerational and transgenerational effects of azoxystrobin on Folsomia candida

Soil organisms are exposed to various pollutants during several generations. However standard toxicity tests are often based on exposure in only one generation. Research of multigenerational (MG) and transgenerational (TG) effects are still quite scarce, however evidence accumulates that effects observed in one generation can be significantly different in some of the following generations, with different effects observed. Some studies suggest adaptation to pollutants, while others report severe effects in following generations. Azoxystrobin is commonly used in the prevention and treatment of fungal diseases in a wide range of economically important crops. The main aim of this study was to assess the toxic effects of azoxystrobin (AZO) on F. candida over 3 generations through the application of biochemical and population level biomarkers. Results of reproduction tests showed a significant decrease in estimated EC50 values, with EC50 for F0 being estimated at 104.44 mga.i./kgD.W.soil and only 15.4 mga.i./kgD.W.soil for F1. In F1 a significant reduction in the number of juveniles was observed, and at AZO concentration of 50 mga.i./kgD.W and higher, F1 did not reproduce. Significant oxidative stress was observed in all generations, with increased SOD and lipid damage that slowly decreased in subsequent generations. Transgenerational effects were also observed, with a significantly reduced number of juveniles in F1 and significant oxidative stress and lipid damage in all generations. IBRv2 showed that F1 was most affected, followed by F0, and least affected was F3. When considering the whole body energy budget, F1 to F3 had significantly higher WBEB compared to F0, and a shift in proportion of energy reserves occurred in F1, where the proportion of lipids increased while protein decreased. Results of this research show that considering standard toxicity tests, risks for populations of soil organisms are possibly severely underestimated. Therefore, standard toxicity guidelines should be supplemented by multigenerational tests, when possible.

On the importance of longer-term exposure to stressors - A critical review and proposal for multigenerational testing in standard soil invertebrates

Standard laboratory tests to describe the impact of stressors (most notably: chemicals) on organisms offer a good compromise between feasibility and outcome, i.e., they should be reproducible and provide robust results. However, these tests may underestimate the potential effects of prolonged exposures, particularly for persistent contaminants. Within the last years, we have observed an increase in studies aiming to target prolonged exposure, e.g., via an extended test duration or by multigenerational (MG) exposure. Seemingly, both reduced and increased impacts have been observed in these studies, but it is also clear that no unique test setup was used, and test designs vary widely among studies. To better describe long term effects, MG is a highly relevant aspect which deserves more consideration at various testing and assessment levels. Therefore, we conducted a literature review focusing on available studies performed with soil invertebrates, exposed to stressors for periods longer than in standard laboratory tests, i.e., full life cycle tests, as well as extensions to standard and MG tests. So far, it has been recommended that such studies should cover more than one generation, but this statement is probably too vague. In this contribution, we summarize and critically discuss the information provided in the literature, and we provide suggestions for future research. The currently available test results from long-term studies have produced clear evidence to recommend the implementation of long-term tests in existing regulatory testing requirements (e.g., for pesticides), in particular for persistent substances and also for delayed effects. Consequently, we recommend the inclusion of such longer exposure test designs (e.g., as annexes) in current OECD and ISO guidelines. However, when doing so, the long-term test designs proposed so far have to be critically adapted for a selected set of representative soil invertebrate test species.

Oral toxicity evaluation of genetically modified lactic acid bacteria in three generations of Sprague Dawley rats

Genetic modification has great advantages in improving performance of bacteria, but its oral safety has not been systematically evaluated. In this study, the toxicity including the reproductive toxicity of two genetically modified bacteria engineered using food-grade vectors on three generations of rats (F0, F1 and F2) were studied. Sprague Dawley rats were administrated by gavage with corresponding parent and genetically modified Lactobacillus plantarum and Lactobacillus delbrueckii at 2.5 × 10 ⁹ CFU every other day for 8 weeks. Results showed that the transgenic Lactobacillus had no significant toxicity to the body weight, food intake or blood biochemical parameters of three generations of rats. There was no significant effect on the reproductive parameters (gestational weight and pregnancy time) and related hormones (FSH, LH, estradiol, progesterone and testosterone) of the parent rats (F0 and F1). Consistently, their offsprings had no abnormal physical conditions including body weight, body length and anogenital distances. Moreover, their pups had normal body organ weight and reasonable abnormal sperm rate. Further analyses were conducted to evaluate SOD, MDA and GPX of the ovarium in the F1 and F2 female rats, which showed no malady phenotypes. In conclusion, transgenic Lactobacillus has no toxicity to the three generations of rats.

Applicability of Enchytraeus bulbosus as a model species in ecotoxicology and risk assessment

Enchytraeus bulbosus is listed in the ISO and OECD standard guidelines as a possible test species of enchytraeid. However, in contrast to other listed species, its applicability in ecotoxicological studies as well as its sensitivity is widely unknown. Therefore, copper, pentachlorophenol(PCP), carbendazim, and chloroacetamide have been investigated by performing two-generation studies with multiple endpoints. Comparable toxicity trends to the existing studies were shown for copper and PCP in the two-generation studies of E. bulbosus. Dose-related abnormal swelling of clitella were found for the first time with PCP and chloroacetamide treatments. Sensitivity comparisons of E. bulbosus to other terrestrial test species were also conducted. E. bulbosus showed high sensitivity, it has comparable sensitivity as other sensitive species of genus Enchytraeus ( E. albidus or E. luxuriosus)to different chemicals, and was more sensitive than E. crypticus and earthworm species ( Eisenia fetida or Eisenia andrei). Combined with the phylogenetic and biological characterization, the results lead to the conclusion that E.bulbosus is a suitable model species in ecotoxicology and the chemical risk assessment (especially in multi-generation) because it has a short generation time, comparatively moderate fecundity, ideal and reasonable sensitivity.

Antibiotic Resistance in the Collembolan Gut Microbiome Accelerated by the Nonantibiotic Drug Carbamazepine

The effects of pharmaceuticals as emerging contaminants in soil on the gut microbiome and antibiotic resistome in nontarget soil fauna are largely elusive. In this study, we explored the composition of the bacterial community and the presence of antibiotic resistance genes (ARGs) in the gut of the model soil collembolan (Folsomia candida) upon antiepileptic drug carbamazepine (CBZ) and antibiotic tetracycline (TC) exposure. Results showed that, individually or in combination, exposure to TC or CBZ significantly altered the gut community structure of F. candida, causing some enrichment of the bacteria associated with xenobiotic metabolism, such as Arthrobacter, Achromobacter, Gordonia, and Shinella. More importantly, oral exposure to the nonantibiotic drug CBZ enhanced the abundance and diversity of ARGs in the gut of F. candida, especially for the beta-lactams and multidrug resistance genes. Our results revealed that the most likely hosts of ARGs in the gut of F. candida were Proteobacteria and Actinobacteria. The significant positive correlation between mobile genetic elements (MGEs) and ARGs indicated the potential risk of ARGs transmission in the gut of F. candida. Overall, the nonantibiotic CBZ is likely to disturb the gut microbiota of nontarget soil fauna such as collembolans, thereby enhancing the dissemination of ARGs.

Transcriptional response of springtail (Folsomia candida) exposed to decabromodiphenyl ether-contaminated soil

Decabromodiphenyl ether (BDE209) is a widely used brominated flame retardant that has become a common soil contaminant of concern due to its persistence and toxicity. However, little is known about molecular-level effects of BDE209 on soil invertebrates. Here, we detected changes in gene transcription of the soil springtail, Folsomia candida, exposed to BDE209 (0.81 mg/kg) in soil for 2, 7 and 14 days. We identified 16 and 771 significantly differentially expressed genes after 2 and 7 days of exposure respectively, and no significantly regulated genes were shared among the two time points. No genes were affected after 14 days of exposure. According to the annotation of the significantly differently expressed genes at 2 and 7 day exposure, we found that BDE209 affected the transcription of genes involved in moulting, neural signal transmission and detoxification. Our results suggested that BDE209 could disrupt moulting of F. candida via the ecdysteroid pathway, and cause neurotoxicity through disrupting some neurotransmitter signalling pathways. This study provided insights into the toxic mechanism of BDE209 on F. candida.

Is nano ZnO/chlorpyrifos mixture more harmful to earthworms than bulk ZnO? A multigeneration approach

As chlorpyrifos is one of the most widely used organophosphorus insecticides and ZnO-NPs are identified as NPs of the highest concern due to their negative effects on aquatic and soil organisms the objective of this study was to evaluate mixture toxicity of CHP and ZnO (bulk and nanoparticles (20 nm)) on two types of soil, artificial (AS) and natural (NS), and over two generations of earthworms. Primary endpoint measured was reproduction inhibition and biochemical biomarkers (acetylcholinesterase, catalase, glutathione-S transferase and malondialdehyde content). Results showed that mixture toxicity differs in respects to all tested factors: soil type, ZnO particle size and earthworm generation. CHP/ZnO mixtures had synergistic effects and significantly reduced a number of juveniles in both generations in AS, while the effects were additive or even antagonistic in NS. There was no difference in reproduction inhibition in respect to particle size of ZnO used in the mixtures. Negative effects could also be detected on growth dynamics of juvenile earthworms (2nd generation) as they had lower initial body mas, reduced growth rate and lower body mass as adults. Measured enzymes responded differently in respect to ZnO particle size used in the mixtures, with CHP/bZnO producing stronger effects. Measured concentrations of the bioavailable Zn in the soils showed no difference in the concentration of bioavailable Zn²⁺ between mixtures, but significantly more Zn²⁺ was retrieved from AS. General biomarker response indicated that 2nd generation of earthworms had lower capability to cope with oxidative stress.

The toxicity of exogenous nickel to soil-dwelling springtail Folsomia candida in relation to soil properties and aging time

Nickel (Ni) is a toxic metal, but studies on Ni toxicity to soil-dwelling springtail are fairly limited, and did not consider the effects of various soil properties and long aging time. To address this, the chronic toxicity of Ni to model organism-Folsomia candida in relation to soil properties and aging time were evaluated in the laboratory study. The results showed that compared to the soils aged only for 7 d, the concentrations causing 50% mortality (LC₅₀) and inhibiting 50% reproduction (EC₅₀) basing measured total Ni in four soils aged for 120 d increased by 1.30-1.94 fold and 1.27-1.82 fold, respectively. Furthermore, the aging effects significantly correlated with soil pH. The toxicity values of Ni differed in ten soils aged for 120 d, the LC₅₀ values were 279-4025 mg/kg and the EC₅₀ values were 133-1148 mg/kg. When calculating the toxicity values basing water soluble and CaCl₂ extracted Ni, the variations in LC₅₀ values between ten soils decreased, while the variations in EC₅₀ values increased. Regression analysis indicated that soil pH was the most important single factor predicting soil Ni toxicity to springtail, the combination of soil pH and OM could best explain Ni toxicity variance in ten soils (89.1% of the variance in LC₅₀ values and 89.6% of the variance in EC₅₀ values).

The toxicity of exogenous arsenic to soil-dwelling springtail Folsomia candida in relation to soil properties and aging time

Arsenic (As) is a toxic metalloid, but studies on As toxicity to soil-dwelling springtails are fairly limited, and did not consider the effects of various soil properties and long aging time. To address this, the toxicity of As to model organism-Folsomia candida were evaluated in the laboratory studies. The results showed that compared to the soils aged only for 15 d, the concentrations inhibiting 50% reproduction (EC₅₀) significantly increased by 1.3- to 2.0-fold in four soils aged for 150 d, the concentrations causing 50% mortality (LC₅₀) were higher than the highest test concentration in the most soils. Furthermore, the aging effects correlated significantly with soil free Fe oxides contents. The toxicity of As differed in ten soils aged for 150 d, the LC₅₀ were 320-> 1280 mg/kg in acute test and the EC₅₀ were 67-580 mg/kg in chronic test. Regression analysis indicated that soil clay was the most important single factor predicting soil As toxicity to reproduction, explaining 89% of the variance in EC₅₀ values. Soil pH, free Fe oxides and Al oxides could also well explain the toxicity variance (> 65%), indicating that As sorption was a key factor controlling its toxicity.

Effects of polyethylene microplastics on the gut microbial community, reproduction and avoidance behaviors of the soil springtail, Folsomia candida

Microplastics (MPs) are an emerging contaminant and are confirmed to be ubiquitous in the environment. Adverse effects of MPs on aquatic organisms have been widely studied, whereas little research has focused on soil invertebrates. We exposed the soil springtail Folsomia candida to artificial soils contaminated with polyethylene MPs (<500 μm) for 28 d to explore the effects of MPs on avoidance, reproduction, and gut microbiota. Springtails exhibited avoidance behaviors at 0.5% and 1% MPs (w/w in dry soil), and the avoidance rate was 59% and 69%, respectively. Reproduction was inhibited when the concentration of MPs reached 0.1% and was reduced by 70.2% at the highest concentration of 1% MPs compared to control. The half-maximal effective concentration (EC₅₀) value based on reproduction for F. candida was 0.29% MPs. At concentrations of 0.5% dry weight in the soil, MPs significantly altered the microbial community and decreased bacterial diversity in the springtail gut. Specifically, the relative abundance of Wolbachia significantly decreased while the relative abundance of Bradyrhizobiaceae, Ensifer and Stenotrophomonas significantly increased. Our results demonstrated that MPs exerted a significant toxic effect on springtails and can change their gut microbial community. This can provide useful information for risk assessment of MPs in terrestrial ecosystems.