Influences of soil properties and leaching on nickel toxicity to barley root elongation

The influence of soil properties on Ni toxicity to barley root elongation was investigated using 17 Chinese soils treated with soluble Ni salts, with and without leaching. The effective concentration of added Ni causing 50% inhibition (EC50) in barley root elongation ranged from 48 to 2519 mg/kg in unleached soils and 46 to >2381 mg/kg in leached soils. Leaching decreased Ni phytotoxicity significantly for approximately 90% of soils, and the effect was most pronounced for soils with pH ≥8.2. Soil pH was the most important factor controlling Ni toxicity in soils, explaining approximately 68% of the variance in unleached and leached EC50 values. Regression models between toxicity thresholds and soil pH, soil organic carbon content, or effective cation exchange capacity were developed. The models showed good agreement with those developed previously for European soils (r²=0.87). These quantitative relationships between Ni toxicity and soil properties are helpful to develop soil-specific guidance on Ni toxicity thresholds for China.     

The Effect of Tributyltin-Oxide on Earthworms, Springtails, and Plants in Artificial and Natural Soils

Chemical bioavailability in Organisation for Economic Co-operation and Development (OECD) artificial soil can contrast with bioavailability in natural soils and produce ecotoxicologic benchmarks that are not representative of species’ exposure conditions in the field. Initially, reproduction and growth of earthworm and Collembolan species, and early seedling growth of a dicotyledonous plant species, in nine natural soils (with a wide range of physicochemical properties) and in OECD soil were evaluated. Soils that supported reproduction and growth of the test species were then used to investigate the toxicity of tributyltin-oxide (TBT-O). Natural soils caused greater toxicity of TBT-O to earthworms (EC₅₀ values varied from 0.5 to 4.7 mg/kg soil dry weight [dw]) compared with toxicity in OECD soil (EC₅₀ = 13.4 mg/kg dw). Collembolans were less sensitive to TBT-O than earthworms in natural soils, with EC₅₀ values ranging from 23.4 to 177.8 mg/kg dw. In contrast, the toxicity of TBT-O to collembolans in OECD soil (EC₅₀ = 104.0 mg/kg dw) was within the range of EC₅₀ values in natural soils. Phytotoxicity tests revealed even greater difference between the effects in natural soils (EC₅₀ values ranged from 10.7 to 189.2 mg/kg dw) and in OECD soil (EC₅₀ = 535.5 mg/kg dw) compared with results of the earthworm tests. Studies also showed that EC₅₀ values were a more robust end point compared with EC₁₀ values based on comparisons of coefficients of variation. These results show that toxicity testing should include studies with natural soils in addition to OECD soil to better reflect exposure conditions in the field.     

Single versus multiple occupancy--effects on toxicity parameters measured on Eisenia fetida in lead nitrate-treated soil

The mortality (7 and 14 d), weight change (7 and 14 d), and metal uptake of Eisenia fetida (Savigny, 1826) kept in Pb(NO3)2-treated Kettering loam soil in single- and multiple-occupancy (10 earthworms) test containers were determined. The number of earthworms to dry mass (g) ratio of soil was 1:50 in both sets of test containers. Lead concentrations were in the nominal range of 0 to 10,000 mg Pb/kg soil (mg/kg hereafter). Levels of mortality at a given concentration were statistically identical between the single- and multiple-occupancy tests, except at 1,800 mg/kg, at which significantly (p < or = 0.05) more mortality occurred in the multiple-occupancy tests. Death of individual earthworms in the multiple-occupancy tests did not trigger death of the other earthworms in that soil. The LC50 values (concentration statistically likely to kill 50% of the population) were identical between the multiple- and single-occupancy soils: 2,662 mg/kg (2,598-2,984, 7 d) and 2,589 mg/kg (2,251-3,013, 14 d) for the multiple-occupancy soils and 2,827 mg/kg (2,443-3,168, both 7 and 14 d) for the single-occupancy soils (values in brackets represent the 95% confidence intervals). Data were insufficient to calculate the concentration statistically likely to reduce individual earthworm mass by 50% (EC50), but after 14 d, the decrease in earthworm weight in the 1,800 and 3,000 mg/kg tests was significantly greater in the multiple- than in the single-occupancy soils. At 1,000, 1,800, and 3,000 mg/kg tests, earthworm Pb tissue concentration was significantly (p < or = 0.05) greater in earthworms from the multiple-occupancy soils. The presence of earthworms increased the NH3 content of the soil; earthworm mortality increased NH3 concentrations further but not to toxic levels.     

Terrestrial toxicity evaluation of decabromodiphenyl ethane on organisms from three trophic levels

Decabromodiphenyl ethane (DBDP-Ethane) was evaluated for its potential to effect sewage sludge respiration, soil nitrification, survival and reproduction in Eisenia fetida, and seedling emergence and growth in Zea mays, Lolium perenne, Glycine max, Allium cepa, Lycopersicon esculentum, and Cucumis sativa. The no observed effect concentrations (NOECs) were identified at the limit concentration level for sewage sludge respiration (>10 mg DBDP-Ethane/kg dry soil), >2500 mg/kg dry soil for soil nitrification, >3720 mg/kg dry soil for earthworm survival, and >6250 mg/kg dry soil for seedling emergence and growth in Z. mays, L. perenne, and G. max . Treatment-related effects were identified for E. fetida reproduction, C. sativa survival, and L. esculentum and A. cepa height and dry weight. The most sensitive endpoints were decreased height and dry weight for A. cepa and decreased reproduction for E. fetida with NOECs of 1563_nominal (1540_measured) and 2210_nominal (1907_{mean measured}) mg/kg dry soil. The NOEC for soil nitrification and the lowest NOEC identified for soil (i.e., A. cepa) were used to derive predicted no effect concentrations (PNEC) values of 2500 mg/kg for sewage sludge and 156 mg/kg for soil. The calculated PNECs indicate DBDP-Ethane presents little risk to organisms in the sewage sludge and soil compartments.     

Phytotoxicity of PFOS and PFOA to Brassica chinensis in different Chinese soils

PFOS and PFOA are potential persistent organic pollutants that have raised many concerns in recent years. Research focusing on phytotoxicity of PFOS and PFOA to higher plants is necessary for their risk assessments. However, few toxicity data exist for PFOS or PFOA and higher plants. Here we investigated phytotoxicity of PFOS and PFOA to Brassica chinensis root growth in six different Chinese soils varying widely in soil properties using a standardized root length assay. The effective concentrations of added PFOS and PFOA causing 50% inhibition (EC₅₀) ranged from 95 to >200 mg kg⁻¹ for PFOS and from 107 to 246 mg kg⁻¹ for PFOA, respectively, representing more than 2.1- and 2.3-fold variation among the tested soils. Regressions of soil PFOS and PFOA toxicity threshold values (EC_x and NOECs) with various soil properties showed that the amount of organic matter was the most significant factor affecting their toxicity to B. chinensis.     

Effects of insect growth regulators on the nontarget soil arthropod Folsomia candida (Collembola)

The aim of this study was to assess the effect of several insect growth regulators (IGRs) on the nontarget soil arthropod Folsomia candida (Collembola). The survival and reproduction rates of F. candida were evaluated after 28 days of exposure to six IGRs (methoprene, fenoxycarb, precocene II, tebufenozide, hexaflumuron and teflubenzuron) and to one herbicide (diuron) in artificial soil. The differences in the sensitivity of F. candida to these different substances are high. The chitin synthesis inhibitors teflubenzuron and hexaflumuron were the most toxic compounds with an EC50 of 0.05 mg/kg (dry weight) for teflubenzuron and an EC50 of 0.6mg/kg for hexaflumuron. Teflubenzuron is toxic for F. candida at concentrations that are probably close to environmental levels of this insecticide. Inhibition of reproduction is strongly related to adult survival for the juvenile hormone agonist methoprene and for the antijuvenile hormone precocene II, with an EC50 of 173 mg/kg and a LC50 of 178mg/kg for methoprene and an EC50 of 15 mg/kg and a LC50 of 26 mg/kg for precocene II. Fenoxycarb, another juvenile hormone analog, showed a dose-response curve for mortality different from that of methoprene; at concentrations such as 3052 mg/kg no effect on adult survival was observed. However, the EC50 value of 113mg/kg is of the same order of magnitude as that obtained for methoprene. A test with compressed soil contaminated with fenoxycarb was conducted to observe parameters such as numbers of eggs laid and juveniles hatched. No differences were observed between these two endpoints for fenoxycarb. An EC50 of 109 mg/kg was obtained for the ecdysone agonist tebufenozide. The herbicide diuron showed a relatively high toxicity for F. candida with an EC50 of 20 mg/kg. Our results show that some of the tested IGRs can have effects on Collembola at environmentally relevant concentrations (toxicity/exposure ratios < 5 for teflubenzuron, hexaflumuron, and diuron).     

Toxicity of four nitrogen-heterocyclic polyaromatic hydrocarbons (NPAHs) to soil organisms

The aims of this study were: (i) to investigate the toxicity of N-heterocyclic polyaromatic hydrocarbons (NPAHs) quinoline, acridine, phenazine, and 1,10-phenanthroline to the soil invertebrates Eisenia fetida, Enchytraeus crypticus, Folsomia candida, and Caenorhabditis elegans, (ii) to compare the toxicity of four NPAHs and the species sensitivity, and (iii) to discuss possible risks of these compounds in soils. Different toxicities were found for the tested NPAHs which might be partially explained by their structure and properties. Effect concentrations expressed as soil pore-water concentrations were related to log K_ow, which indicated narcosis as the most probable mode of toxic action. The species sensitivity decreased in the rank: springtails >enchytraeids=earthworms> nematodes. Predicted no-effect concentration (PNEC) values were calculated for all tested species giving values from 0.5 to 6.8 mg/kg. It is unlikely that there is a risk for soil organisms in natural soils where lower NPAHs concentrations are expected.     

Effect of soil properties on lead bioavailability and toxicity to earthworms

Soil properties are important factors modifying metal bioavailability to ecological receptors. Twenty-one soils with a wide range of soil properties (USA; http://soils.usda.gov/technical/classification/taxonomy/) were amended with a single concentration of Pb (2,000 mg/kg) to determine the effects of soil properties on Pb bioavailability and toxicity to earthworms. Earthworm mortality ranged from 0 to 100% acute mortality following exposure to the same total concentration of Pb (2,000 mg/kg) in amended field soils. Internal Pb concentrations in earthworms ranged from 28.7 to 782 mg/kg, with a mean of 271 mg/kg. Path analysis was used to partition correlations in an attempt to discern the relative contribution of each soil property. Results of path analysis indicated that pH was the most important soil property affecting earthworm mortality (p < 0.01) and internal Pb (p < 0.05). Soil pH was related inversely to mortality and internal Pb, soil solution Pb, and Pb bioavailability. The most important soil property modifying reproduction was amorphous iron and aluminum oxides (FEAL). Because FEAL is rich in pH-dependent cation-exchange sites, several soil properties, including pH, FEAL, and cation-exchange capacity, have a causal effect on Pb adsorption and soluble Pb. Path analysis is useful for assessing contaminated soils with a wide range of soil properties and can assist in ecological risk assessment and remediation decisions for contaminated sites. Soil properties are important factors modifying metal bioavailability and toxicity and should be considered during the ecological risk assessment of metals in contaminated soils.     

Toxicity of uranium, molybdenum, nickel, and arsenic to Hyalella azteca and Chironomus dilutus in water-only and spiked-sediment toxicity tests

A series of laboratory spiked-sediment toxicity tests with the amphipod Hyalella azteca and the midge Chironomus dilutus were undertaken to determine acute and chronic toxicity thresholds for uranium (U), molybdenum (Mo), nickel (Ni), and arsenic (As) based on both whole-sediment (total) and pore water exposure concentrations. Water-only toxicity data were also generated from separate experiments to determine the toxicities of these metals/metalloids under our test conditions and to help evaluate the hypothesis that pore water metal concentrations are better correlated with sediment toxicity to benthic organisms than whole-sediment metal concentrations. The relative toxicity of the four elements tested differed depending on which test species was used and whether whole-sediment or pore water metal concentrations were correlated with effects. Based on measured whole-sediment concentrations, Ni and As were the two most acutely toxic elements to H. azteca with 10-d LC50s of 521 and 532 mg/kg d.w., respectively. Measured pore water concentrations indicated that U and Ni were the two most acutely toxic elements, with 10-d LC50s to H. azteca of 2.15 and 2.05 mg/L, respectively. Based on pore water metal concentrations, the no-observed-effect concentrations (NOECs) for growth were (H. azteca and C. dilutus, respectively) 0.67 and 0.21 mg/L for U, <0.37 and 0.60 mg/L for Ni, and 16.43 and <0.42 mg/L for As. Pore-water lowest-observed-effect concentrations (LOECs) for growth were (H. azteca and C. dilutus, respectively) 2.99 and 0.48 mg/L for U, 0.37 and 2.33 mg/L for Ni, and 58.99 and 0.42 mg/L for As. For U and Ni, results from 96-h water-only acute toxicity tests correlated well with pore water metal concentrations in acutely toxic metal-spiked sediment. This was not true for As where metalloid concentrations in overlying water (diffusion from sediment) may have contributed to toxicity. The lowest whole-sediment LOEC reported here for As was 6.6- and 4-fold higher than the Canadian Council of Ministers of the Environment interim sediment quality guideline and the Canadian Nuclear Safety Commission (CNSC) lowest effect level (LEL), respectively. The lowest whole-sediment LOECs reported here for Ni, U and Mo were 4-, 17.5-, and >260-fold higher, respectively, than the CNSC LELs for these metals/metalloids. Data on pore water metal concentrations in toxic sediment would be a useful addition to future Guidelines documents.     

Suitability of lysosomal membrane stability in Eisenia fetida as biomarker of soil copper contamination

Accumulated metals in soils negatively affect dwelling organisms. Earthworms, which are widespread and perform various essential functions, are able to accumulate metals that can damage the coelomic cells. The aim of this work was to evaluate the effect on Eisenia fetida lysosomal membrane stability both during and after copper exposure, and finally to link this to internal concentrations. E. fetida specimens were exposed to a reference soil and two Cu-spiked soils (35 and 350 mg kg⁻¹ d.w.) for 14 days (uptake period) and then transferred into the reference soil for other 18 days (elimination period). After 3 days of uptake, internal Cu concentrations increased and were higher in the specimens exposed to soils spiked with 350 mg Cu kg⁻¹ d.w. After 2 days of elimination, a strong decrease of internal Cu concentrations was always observed. The lysosomal membrane stability, measured as neutral red retention-times, was approximately 50 min for the earthworms exposed to the reference soils, whereas it decreased, at the end of the uptake period, to 21 and 13 min, respectively, for the organisms exposed to soils spiked with 35 and 350 mg Cu kg⁻¹ d.w. A full recovery of the lysosomal membrane stability was reached after 14 and 18 days of the elimination period, respectively, for the organisms exposed to soils spiked with 35 and 350 mg Cu kg⁻¹ d.w. The neutral-red assay would seem a good biomarker since the lysosomal membrane stability of E. fetida appeared to respond rapidly and strongly to soil copper contamination.     

Bioavailability indices for uranium: Effect of concentration in eleven soils

Bioavailability indices have not been developed for uranium (U) in soils. Eleven soils, covering a broad range in soil properties, were treated to achieve U concentrations ranging from background to 10,000 mg U/kg dry soil. Uptake by radish and beans, accumulation by earthworms and extraction with two chemicals were investigated. The extraction efficiency of NaHCO₃ was very high and reflected total soil U levels rather than bioavailable soil U levels. The extraction efficiency of CH₃COONH₄ was lower and was well correlated to the concentration ratios for plants and earthworms. These latter three indices were all negatively correlated to soil cation exchange capacity and organic matter contents. These indices were not constant across soil U concentrations. In several soils, the bioavailability of U was at a minima in the range of 10 to 100 mg U/kg dry soil. The mechanism for this is not clear, but sublethal toxicity may be involved.     

Microbial Toxicity of Cd and Hg in Different Soils Related to Total and Water-Soluble Contents

Microbial toxicity tests with Cd and Hg and up to 18 soil samples were combined with sorption and solubility measurements. The data ought to indicate to what extent toxic effects of the metals are influenced by sorption and the other factors that may alter their biocidal action. The microbial reduction of Fe(III) oxides to Fe²⁺ions was used as a parameter of microbial activity to calculate the total amounts of Cd and Hg that cause 10, 50, and 90% inhibition [effective doses (ED)₁₀, ED₅₀, ED₉₀]. The corresponding solution concentrations [effective concentrations: (EC)₁₀, EC₅₀, EC₉₀] were derived from Freundlich adsorption isotherms. The very large variability in ED values in different soils (ED₁₀: Cd, 5–95 mg/kg; Hg, 0.125–125 mg/kg) can be related to the sorption and solubility behavior of the metals. Nevertheless, the EC values of both metals also indicate a considerable variation (EC₁₀: Cd, 0.01–1.13 mg/liter; Hg, <0.001–0.041 mg/liter). The influence of soluble soilborne substances on metal speciation is the main reason for their varying toxic potential in different soil solutions. The strong and complex influence of soil properties on the toxicity of heavy metals in soils indicates that both chemical and biological methods of soil analysis are needed to assess the risks of soil contamination adequately.     

Effect of soil properties and aging on the toxicity of copper for Enchytraeus albidus, Enchytraeus luxuriosus, and Folsomia candida

In the present study, the effect of the heavy-metal salt copper chloride (CuCl2.2H2O) in soils freshly spiked (3 d) and aged (70 +/- 10 d; mean +/- SD) was studied in the test species Enchytraeus albidus, E. luxuriosus, and Folsomia candida. Up to nine soils were used: Besides the Organisation for Economic Co-operation and Development (OECD) artificial soil and the Agricultural Testing and Research Agency (Landwirtschaftliche Untersuchungs- und Forschungsanstalt, Speyer, Germany) 2.2 natural standard soils, the others were selected based on the EURO Soil approach, taking into account the effect of different soil parameters (pH, organic matter, grain size distribution, and carbon to nitrogen ratio). Additionally, the effect of the chloride ions was studied separately. The results revealed the following: First, a soil effect was observed; for example, in F. candida, median effective concentrations (EC50s) varied between 262 mg/kg in a sample from the same site as the original EURO Soil 5 soil and greater than 1,000 mg/kg in OECD soil. Second, an aging effect was observed, mainly in F. candida. For example, toxicity of offspring survival was increased twofold in the OECD soil and approximately eightfold with aging in the EURO Soil 7 soil, whereas the enchytraeid species did not react differently after aging. Third, an effect of chloride ions on reproduction of the animals was found; however, this effect was independent of the aging period. Fourth, species variation was seen in terms of sensitivity (EC50), decreasing in the following order: E. luxuriosus > E. albidus > F. candida. Differences in toxicity of offspring survival between enchytraeids and F. candida might be explained by the different routes of uptake.     

Ecotoxicity of a polycyclic aromatic hydrocarbon (PAH)-contaminated soil

Soil samples from a former cokery site polluted with polycyclic aromatic hydrocarbons (PAHs) were assessed for their toxicity to terrestrial and aquatic organisms and for their mutagenicity. The total concentration of the 16 PAHs listed as priority pollutants by the US Environmental Protection Agency (US-EPA) was 2634+/-241 mg/kgdw in soil samples. The toxicity of water-extractable pollutants from the contaminated soil samples was evaluated using acute (Vibrio fischeri; Microtox test, Daphnia magna) and chronic (Pseudokirchneriella subcapitata, Ceriodaphnia dubia) bioassays and the EC values were expressed as percentage water extract in the test media (v/v). Algal growth (EC50-3d=2.4+/-0.2% of the water extracts) and reproduction of C. dubia (EC50-7d=4.3+/-0.6%) were the most severely affected, compared to bacterial luminescence (EC50-30 min=12+/-3%) and daphnid viability (EC50-48 h=30+/-3%). The Ames and Mutatox tests indicated mutagenicity of water extracts, while no response was found with the umu test. The toxicity of the soil samples was assessed on the survival and reproduction of earthworms (Eisenia fetida) and collembolae (Folsomia candida), and on the germination and growth of higher plants (Lactuca sativa L.: lettuce and Brassica chinensis J.: Chinese cabbage). The EC50 values were expressed as percentage contaminated soil in ISO soil test medium (weight per weight-w/w) and indicated severe effects on reproduction of the collembola F. candida (EC50-28 d=5.7%) and the earthworm E. fetida (EC50-28 d=18% and EC50-56 d=8%, based on cocoon and juvenile production, respectively). Survival of collembolae was already affected at a low concentration of the contaminated soil (EC50-28 d=11%). The viability of juvenile earthworms was inhibited at much lower concentrations of the cokery soil (EC50-14 d=28%) than the viability of adults (EC50-14 d=74%). Only plant growth was inhibited (EC50-17d=26%) while germination was not. Chemical analyses of water extracts allowed us to identify inorganic water-extractable pollutants as responsible for toxicity on aquatic species, especially copper for effects on D. magna and C. dubia. The soil toxicity on collembolae and earthworms could be explained by 4 PAH congeners-fluorene, phenanthrene, pyrene, and fluoranthene. Yet, toxicity of the cokery soil as a whole was much lower than toxicity that could be deduced from the concentration of each congener in spiked soils, indicating that pollutants in the soil became less bioavailable with ageing.     

Supercritical carbon dioxide extraction as a predictor of polycyclic aromatic hydrocarbon bioaccumulation and toxicity by earthworms in manufactured-gas plant site soils

The toxicity and uptake of polycyclic aromatic hydrocarbons (PAHs) by earthworms were measured in soil samples collected from manufactured-gas plant sites having a wide range in PAH concentrations (170-42,000 mg/kg) and soil characteristics. Samples varied from vegetated soils to pure lampblack soot and had total organic carbon contents ranging from 3 to 87%. The biota-soil accumulation factors (BSAFs) observed for individual PAHs in field-collected earthworms (Aporrectodea caliginosa) were up to 50-fold lower than the BSAFs predicted using equilibrium-partitioning theory. Acute toxicity to the earthworm Eisenia fetida was unrelated to total PAH concentration: Mortality was not observed in some soils having high concentrations of total PAHs (>42,000 mg/kg), whereas 100% mortality was observed in other soils having much lower concentrations of total PAHs (1,520 mg/kg). Instead, toxicity appeared to be related to the rapidly released fraction of PAHs determined by mild supercritical CO2 extraction (SFE). The results demonstrate that soils having approximately 16,000 mg rapidly released total PAH/kg organic carbon can be acutely toxic to earthworms and that the concentration of PAHs in soil that is rapidly released by SFE can estimate toxicity to soil invertebrates.     

Bioaccumulation of Total and Methyl Mercury in Three Earthworm Species (Drawida sp., Allolobophora sp., and Limnodrilus sp.)

We determined total and methyl mercury contents in soil, three earthworm species and their vomitus to study the species-specific differences of mercury bioconcentration in Huludao City, a heavily polluted region by chlor-alkali and nonferrous metal smelting industry in Liaoning Province, northeast China. Total and methyl mercury contents were 7.20 mg/kg and 6.94 ng/g in soil, 1.43 mg/kg and 43.03 ng/g in Drawida sp., 2.80 mg/kg and 336.52 ng/g in Alolobophora sp., respectively. Total mercury contents were 0.966 mg/kg in Drawida sp. vomitus and 4.979 mg/kg in Alolobophora sp. vomitus, respectively. Total mercury contents in earthworms and their vomitus were significantly species-specific different and were both in decreasing with earthworms body lengths, which might due to the growth dilution. Among the soil, earthworms and their vomitus, total mercury contents were in the order of soil > earthworms > earthworm vomitus. Methyl mercury was about 3.01% of total mercury in Drawida sp., 12.02% of total mercury in Alolobophora sp., respectively. It suggested that mercury was mostly in inorganic forms in earthworms. Bioaccumulation factors of methyl mercury from soil to earthworms were much higher than those of total mercury, which suggested that methyl mercury might be more easily absorbed by and accumulated in earthworms because of its lipid solubility.     

Using the critical body residue approach to determine the acute toxicity of cadmium at varying levels of water hardness and dissolved organic carbon concentrations

The linkage between acute adverse effects of cadmium and internal cadmium levels were investigated for the oligochaete worm Lumbriculus variegatus in water at varying degrees of hardness and two different dissolved organic carbon (DOC) concentrations. The LC₅₀s for the effect of cadmium on the survival of the worms greatly differed depending on water hardness and DOC. We found less variability in internal metal toxicity metrics (lethal residue; LR₅₀s) than in external toxicity metrics (lethal concentration; LC₅₀s): LC₅₀s varied from 2.4 to 66.1 μmol/L, while LR₅₀s varied only from 226 to 413 μmol/kg wet weight. The cadmium body burden appeared to be independent of exposure conditions. From our experimental data, a critical cadmium body residue (324±78 μmol/kg wet weight) associated with 50% lethality was derived. The protective role of DOC and water hardness against cadmium toxicity was evident.     

Sensitivity of the Endogeic Tropical Earthworm <Emphasis Type="Italic">Pontoscolex corethrurus</Emphasis> to the Presence of Heavy Crude Oil

Contamination of soil with petroleum is common in oil-producing areas across the tropical regions of the world. There is limited knowledge on the sensitivity of endogeic tropical earthworms to the contamination of soil with total petroleum hydrocarbons (TPH) present in crude oil. Pontoscolex corethrurus is a dominant species in tropical agroecosystems around oil-processing facilities. The sensitivity of P. corethrurus to soil artificially contaminated with “Maya” Mexican heavy crude oil was investigated through avoidance and acute ecotoxicity tests, using the following measured concentrations: 0 (reference soil), 551, 969, 4845, 9991 and 14,869 mg/kg. The avoidance test showed that P. corethrurus displayed a significant avoidance behavior to heavy crude oil at a concentration of 9991 mg/kg or higher. In contrast, acute toxicity tests indicate that the median lethal concentration (LC₅₀) was 3067.32 mg/kg; however, growth (weight loss) was more sensitive than mortality. Our study revealed that P. corethrurus is sensitive to TPH, thus highlighting the importance of P. corethrurus for petroleum ecotoxicological tests.     

Effects of the Fungicide Benomyl on Earthworms in Laboratory Tests Under Tropical and Temperate Conditions

Soil organisms play a crucial role in the terrestrial ecosystem. Plant protection products (PPPs) are known to affect soil organisms and might have negative impacts on soil functions influenced by these organisms. Little research has been performed to date on the impact of PPPs on tropical soil ecosystems. Therefore, in this study it was investigated whether the effects of the fungicide benomyl (chosen as a model substance) differ between tropical and temperate regions and whether data generated under temperate conditions can be used for the Environmental Risk Assessment (ERA) in tropical regions. The effect of benomyl on earthworms was evaluated in acute and chronic laboratory tests modified for tropical conditions. These tests were performed at two temperatures (20°C and 28°C) and with two strains (temperate and tropical) of the compost worm Eisenia fetida. The fungicide was spiked in two natural and two artificial soils. In addition to the organization for economic cooperation and development (OECD) artificial soil, a tropical artificial soil (TAS), containing a tropical fern product (xaxim) instead of peat, was developed in this study. The results from the laboratory tests and a literature review showed that the effects of benomyl were, on average, lower under tropical conditions (LC₅₀: 450–630 mg active ingredient (a.i.)/kg; EC₅₀: 0.8–12.9 mg a.i./kg) than under temperate conditions (LC₅0: 61–67 mg a.i./kg; EC₅₀: 1.0–1.6 mg a.i./kg) by a maximum factor of 10.3 (acute tests) and 12.9 (chronic tests). This result might be caused by an increased degradation of benomyl, and/or its first metabolite carbendazim, at higher temperatures, but a different sensitivity of the two worm strains cannot be ruled out. Despite the lower toxicity under tropical conditions and assuming comparable application rates, a preliminary assessment confirms the risk of benomyl to soil invertebrates under both conditions.     

Ecotoxicity study of titania (TiO₂) NPs on two microalgae species: Scenedesmus sp. and Chlorella sp

In view of their increasing commercial applications metal oxide NPs like titania have elevated chances of entry to the environment. The ecotoxicity analyses are required to assess their environmental risks. The present work aims to demonstrate the effect of titania NPs on microalgae isolated from freshwater environment (Scenedesmus sp. and Chlorella sp.). The growth inhibitory effect of titania NPs was observed for both the species (72 h EC₅₀ value, 16.12 mg/L for Chlorella sp.; 21.2 mg/L for Scenedesmus sp.). Bulk micron-sized titania also showed toxicity though to a lesser extent (72 h EC₅₀ value, 35.50 mg/L for Chlorella sp.; 44.40 mg/L for Scenedesmus sp.). A concentration dependent decrease in chlorophyll content was observed in the treated cells compared to the untreated ones, more effect being notable in case of NPs. Preliminary results based on FT-IR studies and microscopic images suggest interaction of the NPs with the cell surface.