Neonicotinoid insecticides are successfully applied to control pests in a variety of agricultural crops; however, they may not only affect pest insects but also non-target organisms such as ...pollinators. This review summarizes, for the first time, 15 years of research on the hazards of neonicotinoids to bees including honey bees, bumble bees and solitary bees. The focus of the paper is on three different key aspects determining the risks of neonicotinoid field concentrations for bee populations: (1) the environmental neonicotinoid residue levels in plants, bees and bee products in relation to pesticide application, (2) the reported side-effects with special attention for sublethal effects, and (3) the usefulness for the evaluation of neonicotinoids of an already existing risk assessment scheme for systemic compounds. Although environmental residue levels of neonicotinoids were found to be lower than acute/chronic toxicity levels, there is still a lack of reliable data as most analyses were conducted near the detection limit and for only few crops. Many laboratory studies described lethal and sublethal effects of neonicotinoids on the foraging behavior, and learning and memory abilities of bees, while no effects were observed in field studies at field-realistic dosages. The proposed risk assessment scheme for systemic compounds was shown to be applicable to assess the risk for side-effects of neonicotinoids as it considers the effect on different life stages and different levels of biological organization (organism versus colony). Future research studies should be conducted with field-realistic concentrations, relevant exposure and evaluation durations. Molecular markers may be used to improve risk assessment by a better understanding of the mode of action (interaction with receptors) of neonicotinoids in bees leading to the identification of environmentally safer compounds.
Despite the global importance of forests, it is virtually unknown how their soil microbial communities adapt at the phylogenetic and functional level to long-term metal pollution. Studying 12 sites ...located along two distinct gradients of metal pollution in Southern Poland revealed that functional potential and diversity (assessed using GeoChip 4.2) were highly similar across the gradients despite drastically diverging metal contamination levels. Metal pollution level did, however, significantly impact bacterial community structure (as shown by MiSeq Illumina sequencing of 16S rRNA genes), but not bacterial taxon richness and community composition. Metal pollution caused changes in the relative abundance of specific bacterial taxa, including Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Planctomycetes and Proteobacteria. Also, a group of metal-resistance genes showed significant correlations with metal concentrations in soil. Our study showed that microbial communities are resilient to metal pollution; despite differences in community structure, no clear impact of metal pollution levels on overall functional diversity was observed. While screens of phylogenetic marker genes, such as 16S rRNA genes, provide only limited insight into resilience mechanisms, analysis of specific functional genes, e.g. involved in metal resistance, appears to be a more promising strategy.
Using two distinct gradients of long-term heavy metal pollution, we found that both microbial community composition as well as functional gene-based structure was only minorly affected by the metal pollution, despite strong differences in metal toxicity along the gradients.
There is an increasing awareness of the threats posed by the worldwide presence of microplastics (MPs) in the environment. Due to their high persistence, MPs will accumulate in the environment and ...their quantities tend to increase with time. MPs end up in environments where often also chemical contaminants are present. Since the early 2000s, the number of studies on the sorption of chemicals to plastic particles has exponentially increased. The objective of this study was to critically review the literature to identify the most important factors affecting the sorption of chemical contaminants to MPs. These factors include the physicochemical properties of both the MPs and the chemical contaminants as well as environmental characteristics. A limited number of studies on soil together with an increased notion of the importance of this compartment as a final sink for MPs was observed. Therefore, we assessed the distribution of model chemicals (two PCBs and phenanthrene) in the soil compartment in the presence of MPs using a mass balance model. The results showed a high variation among chemicals and microplastic types. Overall, a higher partitioning to MPs of chemical contaminants in soil is expected in comparison to aquatic environments. As sorption to a large extent determines bioavailability, the effects of combined exposure to chemicals and MPs on the toxicity and bioaccumulation in biota are discussed. Finally, some considerations regarding sorption and toxicity studies using MPs are given.
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•Increasing number of studies investigated the sorption of contaminants to microplastics.•Hydrophobic and electrostatic forces are the main mechanisms for sorption.•Environmental conditions also affect the sorption process.•Higher fractions of contaminant sorbed to microplastics in soil than in aquatic phase.•Sorption may explain the bioavailability of chemicals in the presence of microplastics.
The mechanisms for the sorption of contaminants to microplastics are driven by their interactions, and may greatly affect their environmental fate and toxicity.
Folsomia candida is a model in soil biology, belonging to the family of Isotomidae, subclass Collembola. It reproduces parthenogenetically in the presence of Wolbachia, and exhibits remarkable ...physiological adaptations to stress. To better understand these features and adaptations to life in the soil, we studied its genome in the context of its parthenogenetic lifestyle.
We applied Pacific Bioscience sequencing and assembly to generate a reference genome for F. candida of 221.7 Mbp, comprising only 162 scaffolds. The complete genome of its endosymbiont Wolbachia, was also assembled and turned out to be the largest strain identified so far. Substantial gene family expansions and lineage-specific gene clusters were linked to stress response. A large number of genes (809) were acquired by horizontal gene transfer. A substantial fraction of these genes are involved in lignocellulose degradation. Also, the presence of genes involved in antibiotic biosynthesis was confirmed. Intra-genomic rearrangements of collinear gene clusters were observed, of which 11 were organized as palindromes. The Hox gene cluster of F. candida showed major rearrangements compared to arthropod consensus cluster, resulting in a disorganized cluster.
The expansion of stress response gene families suggests that stress defense was important to facilitate colonization of soils. The large number of HGT genes related to lignocellulose degradation could be beneficial to unlock carbohydrate sources in soil, especially those contained in decaying plant and fungal organic matter. Intra- as well as inter-scaffold duplications of gene clusters may be a consequence of its parthenogenetic lifestyle. This high quality genome will be instrumental for evolutionary biologists investigating deep phylogenetic lineages among arthropods and will provide the basis for a more mechanistic understanding in soil ecology and ecotoxicology.
The aim of this study was to improve our understanding of metal bioavailability in soil by linking the biotic ligand approach with toxicokinetics modelling. We determined cadmium bioaccumulation ...kinetics in Folsomia candida (Collembola) as a function of soil pH. Animals were exposed for 21 days to LUFA 2.2 soil at 5 or 20 μg Cd g−1 dry soil followed by 21 days elimination in clean soil. Internal cadmium concentrations were modelled using a first-order one-compartment model, relating uptake rate constants (k1) to total soil, water or 0.01 M CaCl2 extractable and porewater concentrations. Based on total soil concentrations, k1 was independent of soil pH while it strongly increased with increasing pH based on porewater concentrations explaining the reduced competition of H+ ions making cadmium more bioavailable in pore water at high pH. This shows that the principles of biotic ligand modelling are applicable to predict cadmium accumulation kinetics in soil-living invertebrates.
•Cadmium uptake and elimination in Folsomia candida were investigated.•Animals were exposed to LUFA 2.2 soil at different pH levels.•Langmuir isotherms were used to describe interaction of Ca and protons with Cd.•pH was the main factor affecting Cd toxicokinetics when pore water was considered.
Integrating bioaccumulation kinetics with a BLM approach provides novel insights into the bioavailability of cadmium to springtails in soil.
Wastewater treatment plants (WWTPs) are important routes for releasing microplastics into the environment, with the produced sludge acting as a recipient of microplastics from wastewater. There is ...little information on the impact of sludge processes on the number of microplastics in sludge. In this study, the presence of microplastics in sludge produced by the Sari WWTP in northern Iran was investigated. Samples were taken in 3 replications and microplastics larger than 37 μm were extracted. The sludge from primary settling tank, clarifier, after sludge thickener and after aerobic digester, and after dewatering contained 214, 206, 200, 238, and 129 microplastics/g dry weight, respectively. According to the amount of sludge produced for each unit, this equals 280, 362, 599, 601, and 276 million microplastics/day, respectively, of which more than 85% were fibers. The numbers of microplastics in the sludge from the output of the sludge thickener and the aerobic digester did not significantly differ. However, their numbers decreased by more than 50% after dewatering, probably due to the destruction of flocs in the digestive process and the release of attached microplastics, which are returned into the wastewater treatment process with the rejected water. Polyester and polyethylene were the predominant types of fibers and particles, respectively. Given the annual amount of sludge produced, more than 100 billion microplastics enter the environment per year. Wastewater sludge, therefore, is an important source for the emission of microplastics, especially fibers, to the environment, warranting further evaluation of the associated environmental hazards.
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•Primary and secondary sludge contribute most to the separation of MPs from wastewater.•Fibers are the predominant type of MPs in wastewater sludge.•Dewatering reduced the numbers of MPs in sludge by more than 50%.•Large amounts of MPs are returned to the aeration tank by rejected water.
This study aimed at relating the abundance and diversity of invertebrate communities of urban soils to chemical and physical soil characteristics and to identify the taxa most sensitive or tolerant ...to soil stressors. The invertebrate community of five urban soils in Naples, Italy, was sampled. To assess soil quality invertebrate community indices (Shannon, Simpson, Menhinick and Pielou indices), Acarina/Collembola ratios, and the soil biological quality index (QBS) were calculated. The chemical and physical characteristics of the soils strongly differed. Abundance rather than taxa richness of invertebrates were more affected by soil characteristics. The community was more abundant and diverse in the soils with high organic matter and water content and low metal (Cu, Pb, Zn) concentrations. The taxa more resistant to the urban environment included Acarina, Enchytraeids, Collembola and Nematoda. Collembolans appeared particularly sensitive to changing soil properties. Among the investigated indices, QBS seems most appropriate for soil quality assessment.
► The abundance and diversity of invertebrate communities was related to properties and metal contents of urban soils. ► Several (biodiversity) indices were calculated and compared to evaluate soil quality. ► Metal contamination affected invertebrate density and diversity. ► The taxa more tolerant to metal contamination were Acarina, Enchytraeids, Collembola and Nematoda. ► The soil biological quality index QBS index was most appropriate for soil quality assessment.
Soil metal contamination negatively affected soil invertebrate abundance and diversity.
To assess the effect of long-term dissolution on bioavailability and toxicity, triethoxyoctylsilane coated and uncoated zinc oxide nanoparticles (ZnO-NP), non-nano ZnO and ZnCl2 were equilibrated in ...natural soil for up to twelve months. Zn concentrations in pore water increased with time for all ZnO forms but peaked at intermediate concentrations of ZnO-NP and non-nano ZnO, while for coated ZnO-NP such a clear peak only was seen after 12 months. Dose-related increases in soil pH may explain decreased soluble Zn levels due to fixation of Zn released from ZnO at higher soil concentrations. At T = 0 uncoated ZnO-NP and non-nano ZnO were equally toxic to the springtail Folsomia candida, but not as toxic as coated ZnO-NP, and ZnCl2 being most toxic. After three months equilibration toxicity to F. candida was already reduced for all Zn forms, except for coated ZnO-NP which showed reduced toxicity only after 12 months equilibration.
► Triethoxyoctylsilane coated ZnO-NP is more toxic than uncoated ZnO-NP. ► ZnO-NP addition causes Zn porewater concentrations to increase for >1 year. ► Soluble Zn decreases at higher concentrations due to dose-related increases in pH. ► Toxicity of uncoated ZnO-NP to F. candida decreased after 3 months equilibration. ► Toxicity of triethoxyoctylsilane coated ZnO-NP decreased only after one year.
ZnO-NP addition causes Zn porewater concentrations to increase for more than one year, with higher toxicity for coated than for uncoated ZnO-NP.
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