Effect of ageing and chemical form on the bioavailability and toxicity of Pb to the survival and reproduction of the soil invertebrate Enchytraeus crypticus

Multixenobiotic response of Collembola to soil contamination, the phisiological basis for bioindicative environmental monitoring

Collembola are well-established models in ecotoxicological research, extensively employed to investigate the effects of various contaminants, including heavy metals. The Multixenobiotic Resistance Mechanism (MXR) is a physiological response based on transmembrane efflux proteins that play a pivotal role in pumping xenobiotics and conferring resistance. This mechanism is firmly established as a biomarker of aquatic contamination and has recently shown promise as a soil biomonitoring tool. In this study, we aimed to assess the feasibility of utilizing the MXR mechanism as a biomonitoring tool, specifically by investigating the response of two Collembola species exposed to soil contaminated in a real-life situation. Soil samples were obtained from the site of Brazil's largest mine disaster, a dam rupture in Brumadinho-MG. We explored MXR activity in the model species Folsomia candida and a tropical native species, Cyphoderus sp. Our findings reveal efflux activity in both species, confirmed by model MXR protein inhibitors. Moreover, we observed distinct MXR activity levels corresponding to the degree of heavy metal contamination in the soil samples. Consequently, our results underscore the potential of combining an established soil bioindicator, such as Collembola, with the physiological response of a molecular biomarker like MXR. This approach may represent a valuable strategy for biomonitoring terrestrial ecosystems.

Soil habitat function after innovative nanoagriproducts application: Effect of ageing on the avoidance behaviour of the soil invertebrates Enchytraeus crypticus and Folsomia candida

Research on nanotechnology with applications in agriculture has been gathering attention because it may achieve a good balance between agricultural production and environmental integrity. Among the vast nanomaterials, layered double hydroxides (LDHs) are a promising solution for supplying crops with macro- and/or micronutrients. Still, little is known about their safety implications for non-target organisms, such as soil invertebrates. The habitat function of soils might be impacted by potential stressors, which can be assessed through avoidance behaviour tests. This study aimed to assess the effect of two innovative agriproducts, Zn-Al-NO3 LDH and Mg-Al-NO3 LDH, on the avoidance behaviour of the enchytraeid Enchytraeus crypticus and the collembolan Folsomia candida, over time. Simultaneously, Zn and Mg potential release from LDHs to soil was evaluated. Overall, the behaviour of soil invertebrates differed between species, with enchytraeids being more sensitive to LDHs-treated soils than collembolans, possibly explained by their different physiological traits. The behaviour of soil organisms also depended on the LDH structural composition and was time-variable. Soil treated with Zn-Al-NO3 LDH was perceived as less favourable compared to Mg-Al-NO3 LDH, which was preferred to clean soil at most tested concentrations. LDHs toxicity was partly, but not exclusively, related to Zn and Mg release. Cations release over time was demonstrated in the chemical assessment. Still, LDHs toxicity to soil invertebrates decreased as increasing AC50 values were derived over time. Slower dissolution over time might explain the decrease in toxicity. Our study demonstrates that both soil invertebrates could sense LDHs in soil and eventually adapt their behaviour by avoiding or preferring, according to the type and level of LDH present.

Predicting the thresholds of metals with limited toxicity data with invertebrates in standard soils using quantitative ion character-activity relationships (QICAR)

Terrestrial invertebrates are often used as indicator organisms in ecological risk assessments. However, determining the risk of metals to invertebrates is laborious and time-consuming due to the lengthy testing and ethical approval procedures. In this study, a review of the literature was conducted to provide toxicity data for two standard soils (OECD and LUFA 2.2). An attempt was made to establish models for predicting the toxicity of elements to invertebrates using quantitative ion character-activity relationships (QICARs). In OECD soil, the element toxicity of four groups (Enchytraeus albidus mortality and reproduction, Folsomia candida and Eisenia fetida reproduction) showed significant correlations with atomic number, atomic mass and atomic ionization potential (0.852 ≤ R² ≤ 0.989, P < 0.05). For LUFA 2.2 soil, polarization force parameters and boiling point were most significant parameters for toxicity values of F. candida and Enchytraeus crypticus, respectively (0.866 ≤ R² ≤ 0.962, P < 0.05). Finally, QICAR models were established, and LC₅₀ or EC₅₀ of elements were predicted. Then, models were verified using standard and natural soils, and showed that errors between observed and predicted logLC₅₀/EC₅₀ were mostly < 0.5 orders of magnitude. Thus, the developed QICAR models have potential for predicting the toxicity of elements for soils.

Are structural and functional endpoints of soil communities similarly affected by metal mixtures? - A terrestrial model ecosystem approach

Soils are habitat to a variety of flora and fauna in a linked ecosystem which provides essential ecosystem services. In soil, metals can accumulate at high concentrations, because of anthropogenic activities, leading to toxic effects, threatening the ecosystem and the services it provides. In most real-world contamination scenarios, metals occur as complex mixtures which can interact and produce different toxicity than predicted from individual metal data. Current regulatory guidelines are based on single species responses to individual metals and ignore indirect effects inherent to the inter-linked nature of ecosystems. Also, the evaluation of anthropogenic impacts to the soil communities is usually measured through structural endpoints (e.g. abundance) disregarding functional measurements (e.g. organic matter decomposition rates), which are often seen as tightly related, and thus, similarly affected. In this study we tested three mixture ratios of five metal oxides (lead, copper, nickel, zinc, cobalt) at three dose levels (Low, Med, High) in a terrestrial model ecosystem experiment and measured structural and functional endpoints. Exposure to metal mixtures for 16 weeks did not affect the microarthropod community, but produced severe effects on soil microbial activity (PNR and DHA) reducing activity below 50% compared to control levels, in all dosed treatments. Metal contamination also significantly affected feeding activity and organic matter decomposition, but effects were not as pronounced as on microbial activity. Data suggest that, in the risk assessment of metals and their mixtures, effects on ecosystem structure and functions must be considered to provide adequate environmental protection.

Biochar and urban solid refuse ameliorate the inhospitality of acidic mine tailings and foster effective spontaneous plant colonization under semiarid climate

Phytomanagement is considered a suitable option in line with nature-based solutions to reduce environmental risks associated to metal(loid) mine tailings. We aimed at assessing the effectiveness of biochar from pruning trees combined with compost from urban solid refuse (USR) to ameliorate the conditions of barren acidic (pH ~5.5) metal(loid) mine tailing soils (total concentrations in mg kg^-1: As ~220, Cd ~40, Mn ~1800, Pb ~5300 and Zn ~8600) from Mediterranean semiarid areas and promote spontaneous plant colonization. Two months after amendment addition were enough to observe improvements in chemical and physico-chemical tailing soil properties (reduced acidity, salinity and water-soluble metals and increased organic carbon and nutrients content), which resulted in lowered ecotoxicity for the soil invertebrate Enchytraeus crypticus. Recalcitrant organic carbon provided by biochar remained in soil whereas labile organic compounds provided by USR were consumed over time. These improvements were consistent for at least one year and led to lower bulk density, higher water retention capacity and higher scores for microbial/functional-related parameters in the amended tailing soil. Spontaneous growth of native vegetation was favored with amendment addition, but adult plants of remarkable size were only found after three years. This highlights the existence of a time-lag between the positive effects of the amendment on tailing soil properties being observed and these improvements being translated into effective spontaneous plant colonization.

Laboratory versus field soil aging: Impacts on cadmium distribution, release, and bioavailability

To date, most studies about the aging of metals in soil were based on the controlled laboratory experiments, and few works have attempted to investigate how aging process influences the distribution and bioavailability of metals in soil under the field condition. The purpose of this study was to compare the aging of cadmium (Cd) in soils under the controlled laboratory and the field by monitoring time-dependent soil Cd speciation changes, Cd release kinetics, and Cd bioavailability to plant through the 438-day aging experiments. During the aging process, the proportions of Cd associated with the most weakly bound fraction tended to decrease, with corresponding increases in the more stable binding fractions. After aging, a higher concentration of available Cd was found in the field aging soil (0.74 mg kg^-1) than the laboratory aging soil (0.65 mg kg^-1). The Elovich equation was the best model to describe the soil available Cd aging process. The constant b in the Elovich equation, which was defined as the transformation rate, was in the order of laboratory aging soil > field aging soil. Moreover, higher Cd release amounts were found for the field aging soil (2.74 mg kg^-1) than the laboratory aging soil (2.57 mg kg^-1) at the end of aging. Additionally, higher body Cd concentrations were found for the vegetables grown in the field aging soils (1.49 mg kg^-1, fresh weight) than those grown in the laboratory aging soils (1.32 mg kg^-1, fresh weight). Therefore, this study indicated that the metal distribution process and its bioavailability may be overestimated or underestimated if research data from the laboratory experiments are used to derive soil quality criteria or investigate soil metal bioavailability.

Compartmentation and effects of lead (Pb) in the collembolan, Folsomia candida

The impact of soil lead (Pb) pollution on survival, growth, and reproduction of the collembolan, Folsomia candida, and Pb compartmentation in its gut and remaining body parts were studied by exposing animals to laboratory-spiked soil. The survival, growth, and reproduction of F. candida were significantly reduced by increasing soil Pb concentration. The LC₅₀ values of survival based on total and CaCl₂-extractable Pb concentration in soil were 2562 mg kg^-1 and 351 mg kg^-1, respectively. The EC₅₀ values of reproduction were 1244 mg kg^-1 and 48 mg kg^-1, respectively. The Pb concentration in whole body, gut, and remaining body parts was significantly increased with the increase of soil Pb concentration and followed an exponential increase when the soil Pb concentration was equal to or above a threshold (1000 mg kg^-1 for whole body and remaining body part, 500 mg kg^-1 for gut). Below this threshold, these relationships were linear. The Pb concentration in the gut was higher than whole body and remaining body part of F. candida, and the threshold of internal Pb concentration at which F. candida can compensate was in the range 7-13 mg Pb kg^-1 dry animal (corresponding to soil Pb concentration 500-1000 mg Pb kg^-1 dry soil). The results indicate that reproduction of F. candida was a more sensitive indicator of lead toxicity than survival and growth. Pb was mainly accumulated in the gut of F. candida. We discuss the internal Pb concentration as an indicator of adverse effects in the risk assessment of soil Pb pollution.

Are there any risks of the disposal of pesticide effluents in soils? Biobed system meets ecotoxicology ensuring safety to soil fauna

The biobed is a purification system, which reduces soil pollution for receiving pesticide residues from handling and washing machinery in agricultural areas. The aims of this study were (1) to assess ecotoxicity effects over time to soil fauna, posed by Lorsban^® 480 BR (Chlorpyrifos) and Dithane^® NT (Mancozeb) residues when disposed of in a biobed system compared with two subtropical soils, and (2) to assess ecotoxicity effects over time to soil fauna simulating an accidental spillage with Lorsban^® 480 BR at the biobed. A semi-field experiment was conducted for 420 days in southern Brazil, testing continuous disposal of washing pulverization tanks in biobeds, Typic Haploperox or Typic Hapludults. In addition, different biobeds received a single dose (1 L) of Lorsban^® 480 BR to simulate an accidental spillage. Chronic ecotoxicity tests were performed using Folsomia candida, Eisenia andrei, and Enchytraeus crypticus in different sampling times for both experiments. F. candida was the most sensitive species. The biobed system was able to eliminate effects from residues of both pesticides over time in all species, which did not happen in both natural soils. In accidental spillage simulation, even 420 days after contamination, F. candida did not show reproduction. The biobeds can be a feasible alternative for the disposal and treatment residues of pesticides, also for handling and washing pesticides activities. The system was efficient in promoting degradation and reducing ecotoxicity effects posed by Lorsban^® 480 BR and Dithane^® NT for soil fauna. It is a safe alternative to avoid soil contamination.

Metal oxides and annealed metals as alternatives to metal salts for fixed-ratio metal mixture ecotoxicity tests in soil

In soil metal ecotoxicology research, dosing is usually performed with metal salts, followed by leaching to remove excess salinity. This process also removes some metals, affecting metal mixture ratios as different metals are removed by leaching at different rates. Consequently, alternative dosing methods must be considered for fixed ratio metal mixture research. In this study three different metal mixture dosing methods (nitrate, oxide and annealed metal dosing) were examined for metal concentrations and toxicity. In the nitrate metal dosing method leaching reduced total metal retention and was affected by soil pH and cation exchange capacity (CEC). Acidic soils 3.22 (pH 3.4, CEC 8 meq/100g) and WTRS (pH 4.6, CEC 16 meq/100g) lost more than 75 and 64% of their total metals to leaching respectively while Elora (6.7 pH, CEC 21 meq/100g) and KUBC (pH 5.6, CEC 28 meq/100g) with higher pH and CEC only lost 13.6% and 12.2% total metals respectively. Metal losses were highest for Ni, Zn and Co (46.0%, 63.7% and 48.4% metal loss respectively) whereas Pb and Cu (5.6% and 20.0% metal loss respectively) were mostly retained, affecting mixture ratios. Comparatively, oxide and annealed metal dosing which do not require leaching had higher total metal concentrations, closer to nominal doses and maintained better mixture ratios (percent of nominal concentrations for the oxide metal dosing were Pb = 109.9%, Cu = 84.6%, Ni = 101.9%, Zn = 82.3% and Co = 97.8% and for the annealed metal dosing were Pb = 81.7%, Cu = 80.3%, Ni = 100.5%, Zn = 89.2% and Co = 101.3%). Relative to their total metal concentrations, nitrate metal dosing (lowest metal concentrations) was the most toxic followed by metal oxides dosing while the annealed dosing method was generally non-toxic. Due to the lack of toxicity of the annealed metals and their higher dosing effort, metal oxides, are the most appropriate of the tested dosing methods, for fixed-ratio metal mixtures studies with soil invertebrates.

Lead was mobilized in acid silty clay loam paddy soil with potassium dihydrogen phosphate (KDP) amendment

The immobilization effectiveness between Pb and phosphorus in soil varies with soil types. To clarify the effect of phosphate on the availability of Pb in agricultural soil, a culture experiment with three types of paddy soil was performed with potassium dihydrogen phosphate (KDP) added. EDTA, DGT and in-situ solution extraction methods were used to represent different available Pb content. Results showed that the concentration of EDTA-Pb in HN soil was slightly elevated after exogenous KDP added. The supplement of 300 mg/kg KDP significantly increased the content of soluble Pb in both acid silty clay loam soil and neutral silty loam soil (increased by 104.65% and 65.12%, respectively). However, there was no significant influence of KDP on the concentration of DGT extracted Pb. XANES results showed that Pb(OH)₂, PbHPO₄, humic acid-Pb and GSH-Pb were the major speciation of Pb in soil colloids. The proportion of Pb(OH)₂ and humic acid-bounded Pb in soil colloids were elevated after exogenous KDP added. Our results indicated that there was a mobilization effect of KDP on Pb by increasing the amount of colloidal Pb in soil solution, especially in acid silty clay loam paddy soil. Such colloid-facilitated transport might promote the uptake of Pb in rice and pose a potential threat to human health.