Effects of biochar and foliar application of selenium on the uptake and subcellular distribution of chromium in Ipomoea aquatica in chromium-polluted soils.

The potential toxicity of Cr to plants poses a severe threat to human health. Biochar and Se can reduce the absorption of Cr and its phytotoxicity in plants, but the associated mechanisms at subcellular levels have not been addressed in depth. A study was designed to investigate the effects of biochar, foliar application of Se, and their combination on the physicochemical and biological properties of the soil, Cr availability, Cr absorption, and Cr subcellular distribution in each part of the plant, and biomass and quality of two water spinach (Ipomoea aquatica) genotypes. The results showed that biochar, Se, and their combination increased the organic matter content and available NPK nutrients in the soil and improved the urease, phosphatase, catalase, and sucrase activities in the soil. Furthermore, they also increased the number of bacteria, actinomycetes, and fungi in the soil, were conducive to dry matter accumulation in I. aquatica, and increased the contents of soluble sugar and soluble protein in its leaves. The Cr contents in the roots and shoots of I. aquatica under different treatments were reduced compared with those in the control group. The content of Cr(VI) in the root-soil of I. aquatica with low Cr accumulation and the contents of Cr in various parts of I. aquatica were lower than those in I. aquatica with high Cr accumulation, and the absorbed Cr was mainly accumulated in the roots. Cr was mainly distributed in the cell walls and soluble fractions of the roots, stems, and leaves of I. aquatica and was less distributed in the organelles. Biochar and Se helped to increase the proportion of Cr in the cell walls of the roots and soluble fractions of the leaves of I. aquatica. The effects of improving the soil properties, passivating and inhibiting Cr absorption by I. aquatica, and reducing the Cr proportion in the organelles of biochar were superior to those of Se application. The foliar application of Se and biochar had no synergistic effect on inhibiting Cr absorption by I. aquatica. Based on these findings, the application of biochar in Cr-contaminated soil or foliar application of Se with low Cr-accumulating plants may be effective means of reducing the Cr absorption by plants and its toxicity to ensure the safe production of agricultural products in Cr-contaminated regions.

Responses of two kidney bean (Phaseolus vulgaris) cultivars to the combined stress of sulfur deficiency and cadmium toxicity.

Plants suffer from combined stress of sulfur deficiency and cadmium toxicity in some agricultural lands. However, little is known about the reaction in plants, such as responses in antioxidant enzymes and non-protein thiol compounds, to such combined stress. Therefore, in this study, four treatments, S-sufficiency (TS-Cd), S-deficiency (T-S-Cd), Cd stress (TS+Cd) and combined stress of S-deficiency and Cd stress (T-S+Cd), were set up to investigate (1) the effects of sulfur deficiency or sulfur sufficiency on Cd toxicity to kidney bean cultivar seedlings and the related mechanisms, and (2) the responses of two kidney bean cultivars to combined stress of S-deficiency and Cd-tolerance. The results showed significant increases in hydrogen peroxide (H2O2) and malondialdehyde contents and significant increases in antioxidant enzyme (superoxide dismutase, catalase, peroxidase, and glutathione S-transferase) activities and non-protein thiol compounds (non-protein thiols, reduced glutathione, phytochelatins) synthesis in the plants in TS+Cd and T-S+Cd. On the tissue level, higher proportion of Cd was found to be immobilized/deposited in roots, while on the sub-cell level, higher proportion of Cd was located in cell walls and vacuole fractions with lower in cell organelles. Taken together, the results indicated that Cd detoxification was achieved by the two kidney bean cultivars through antioxidant enzyme activation, non-protein thiol compound synthesis and sub-cellular compartmentalization. In addition, the results indicated that sufficient S supply helped to relieve Cd toxicity, which is of special significance for remediation or utilization of Cd-contaminated soils as S is a plant essential nutrient.

Survival strategies in arsenic-contaminated environments: Comparative insights from native and exotic aquatic species.

The aim of this work was to study the sublethal effects, biokinetics, subcellular partitioning and detoxification of arsenic in two native Chinses species, Bellamya quadrata and Cipangopaludina cathayensis, as well as an exotic South American species, Pomacea canaliculata. The exotic species exhibited higher tolerance than native species. Physiologically based pharmacokinetic model results showed that the exotic species P. canaliculata exhibited a lower bioaccumulation rate and a greater metabolism capacity of As. Subcellular partitioning of As revealed that P. canaliculata exhibits superior As tolerance compared to the native species B. quadrata and C. cathayensis. This is attributed to P. canaliculata effective management of the metal sensitive fraction and enhanced accumulation of As in the biologically detoxified metal fraction. Under As stress, the biochemical parameters (superoxide dismutase, malondialdehyde, glutathione and glutathione S-transferase) of the exotic species P. canaliculata changed less in the native species, and they returned to normal levels at the end of depuration period. Our study provides evidence of the superior survival capability of the exotic species P. canaliculata compared to the native species B. quadrata and C. cathayensis under environmentally relevant levels of As contamination.

Effects of arsenic on gut microbiota and its bioaccumulation and biotransformation in freshwater invertebrate.

This study aimed to investigate the impact of arsenic stress on the gut microbiota of a freshwater invertebrate, specifically the apple snail (Pomacea canaliculata), and elucidate its potential role in arsenic bioaccumulation and biotransformation. Waterborne arsenic exposure experiments were conducted to characterize the snail's gut microbiomes. The results indicate that low concentration of arsenic increased the abundance of gut bacteria, while high concentration decreased it. The dominant bacterial phyla in the snail were Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota. In vitro analyses confirmed the critical involvement of the gut microbiota in arsenic bioaccumulation and biotransformation. To further validate the functionality of the gut microbiota in vivo, antibiotic treatment was administered to eliminate the gut microbiota in the snails, followed by exposure to waterborne arsenic. The results demonstrated that antibiotic treatment reduced the total arsenic content and the proportion of arsenobetaine in the snail's body. Moreover, the utilization of physiologically based pharmacokinetic modeling provided a deeper understanding of the processes of bioaccumulation, metabolism, and distribution. In conclusion, our research highlights the adaptive response of gut microbiota to arsenic stress and provides valuable insights into their potential role in the bioaccumulation and biotransformation of arsenic in host organisms. ENVIRONMENTAL IMPLICATION: Arsenic, a widely distributed and carcinogenic metalloid, with significant implications for its toxicity to both humans and aquatic organisms. The present study aimed to investigate the effects of As on gut microbiota and its bioaccumulation and biotransformation in freshwater invertebrates. These results help us to understand the mechanism of gut microbiota in aquatic invertebrates responding to As stress and the role of gut microbiota in As bioaccumulation and biotransformation.

Effects of naturally aged microplastics on the distribution and bioavailability of arsenic in soil aggregates and its accumulation in lettuce.

Naturally aged microplastics (NAMPs) and arsenic (As) have been reported to coexist in and threaten potentially to soil-plant ecosystem. The research explored the combined toxic effects of NAMPs and As to lettuce (Lactuca sativa L.) growth, and the distribution, accumulation and bioavailability of As in soil aggregates. The As contaminated soil with low, medium and high concentrations (L-As, M-As, H-As) were treated with or without NAMPs, and a total of six treatments. The results displayed that, in comparison to separate treatments of L-As and M-As, the presence of NAMPs increased the total biomass of lettuce grown at these two As concentrations by 68.9 % and 55.4 %, respectively. Simultaneous exposure of NAMPs and L-As or M-As led to a decrease in As content in shoot (0.45-2.17 mg kg-1) and root (5.68-14.66 mg kg-1) of lettuce, indicating an antagonistic effect between them. In contrast, co-exposure to H-As and NAMPs showed synergistic toxicity, and the leaf chlorophyll and nutritional quality of lettuce were also reduced. NAMPs altered the ratio of different soil aggregate fractions and the distribution of bioavailable As within them, which influenced the absorption of As by lettuce. In conclusion, these direct observations assist us in enhancing the comprehend of the As migration and enrichment characteristics in soil-plant system under the influence of NAMPs.

Transcriptomic and metabolomic analysis of the mechanisms underlying stress responses of the freshwater snail, Pomacea canaliculata, exposed to different levels of arsenic.

Arsenic (As) pollution poses an important problem, but limited information is available about the physiological effects of As on freshwater invertebrates. Here, we investigated the physiological effects of chronic As exposure on Pomacea canaliculata, a freshwater invertebrate. High level of As (Ⅲ, 5 mg/L) inhibited the growth of P. canaliculata, whereas low level of As (Ⅲ, 2 mg/L) promoted growth. Pathological changes in shell and cellular ultrastructure due to As accumulation likely explain the growth inhibition at high As level. Low level of As simulated the expression of genes related to DNA replication and chitosan biosynthesis, potentially accounting for the growth promotion observed. High level of As enrichment pathways primarily involved cytochrome P450, glutathione, and arachidonic acid-mediated metabolism of xenobiotics. ATP-binding cassette (ABC) transporters, specifically the ABCB and ABCC subfamilies, were involved in As transport. Differential metabolites were mainly associated with the metabolism and biosynthesis of amino acids. These findings elucidate the dose-dependent effects of As stress on P. canaliculata growth, with low levels promoting and high levels inhibiting. Additionally, our findings also provide insights into As metabolism and transport in P. canaliculata.

Individual and joint toxicity of three chloroacetanilide herbicides to freshwater cladoceran Daphnia carinata.

Individual and joint toxicity of three chloroacetanilide herbicides to a freshwater cladoceran were studied. The 48 h-LC50 values of alachlor, acetochlor and butachlor to Daphnia carinata Dc42 were 11.1, 11.8 and 3.45 mg L(-1), respectively. The toxicity was significantly (p < 0.05) related to hydrophobicity. The additive indexes of binary mixtures of three herbicides were less than zero and it showed antagonism. The body length of D. carinata treated with high concentration of herbicides was shorter than that of control group significantly (p < 0.05). It suggests that joint actions must be considered when assessing the acute toxicity of chloroacetanilide herbicides to D. carinata.

Polyaspartic acid assisted-phytoremediation of cadmium-contaminated farmland: Phytoextraction efficiency, soil quality, and rhizosphere microbial community.

Cadmium is highly toxic and one of the most dangerous metal pollutants in soil, and poses a serious threat to human health through soil-crop-food chain transmission. Polyaspartic acid (PASP) is a biodegradable additive that is environment-friendly compared to traditional chelating agents. Current studies have explored its effect on auxiliary phytoextraction at a laboratory scale; however, the method is still rarely reported at the field scale. Therefore, this study used two ecotypes of Pennisetum sinese in a field experiment for 3 years in Jiaoxi Township, Liuyang City, Hunan Province, China, to understand the effect of PASP on the phytoremediation of Cd-contaminated soil and soil quality through long-term field studies. Moreover, because the soil microbial community responds well to the phytoremediation effect of heavy metal (including Cd)-contaminated soil, the changes in rhizosphere soil microbial community diversity and composition were analyzed. After 2 years of PASP-enhanced phytoremediation, the PASP application increased the total Cd reduction in soil by 237 % and 255 %, and the soil DTPA-extractable Cd content decreased to 0.092 and 0.087 mg kg-1. When the application of PASP ceased in the third year, the two ecotypes of P. sinese obtained after harvest could achieve feed safety. Our study showed that the application of PASP could significantly increase the Cd extraction capacity and shoot biomass of P. sinese, and maintain soil health by optimizing the composition and structure of rhizosphere bacterial communities. The rhizosphere bacterial community structure was improved and dominated by Acidobacteriota, Proteobacteria, and Chloroflexi at the phylum level, and the increased abundance of Acetobacter, Enterobacter, Pseudomonas, and Stenotrophomonas at the genus level may promote heavy metal detoxification in soil, plant growth, and phytoremediation. Long-term field monitoring demonstrated that the low-cost and eco-friendly features of PASP made it a good candidate for enhancing phytoextraction efficiency and regulating soil microbial communities for remediation.

Acute toxicity of butachlor and atrazine to freshwater green alga Scenedesmus obliquus and cladoceran Daphnia carinata.

Both single and joint toxicity of atrazine and butachlor to freshwater green alga Scenedesmus obliquus and cladoceran Daphnia carinata isolated from South China were investigated in the present study. The 96 h-EC(50) values of atrazine and butachlor to S. obliquus were 0.0147 and 2.31 mg L(-1), while the 48 h-LC(50) values to D. carinata were 60.6 and 3.40 mg L(-1), respectively. These results suggest that atrazine could be highly toxic to S. obliquus and slightly toxic to D. carinata, while butachlor exhibits moderate toxicity to both organisms. The additive indexes of atrazine and butachlor mixtures were -2.68 (-3.02 to -2.32) to S. obliquus and 0.054 (-0.025 to 0.238) to D. carinata, respectively. Therefore, the joint action of two herbicides was significant antagonism to S. obliquus, while significant synergism was not shown to D. carinata. Moreover, significant linear correlation between the natural logarithm of herbicide concentrations and growth rates of alga S. obliquus was observed. Taken together, it is the first study reporting the toxicity endpoints for mixture of atrazine and butachlor against S. obliquus and D. carinata isolated from south China. The present results would be helpful to provide data to assess the ecological risk of both herbicides to aquatic organisms.

Interaction between BSM-contaminated soils and Italian ryegrass.

The interaction among the bensulfuron-methyl, growth of Italian ryegrass, and soil chemical/biochemical/microbiological parameters was investigated in a microcosm experiment. The bensulfuron-methyl added to the soil can be rapidly degraded by certain fungi and actinomycetes present in the original paddy rice soil. The growth of Italian ryegrass significantly accelerated the in-soil degradation of bensulfuron-methyl in its rhizosphere. The uptake of bensulfuron-methyl by ryegrass increased with increasing dosage level of bensulfuron-methyl. However, the phytoextraction of bensulfuron-methyl by ryegrass contributed insignificantly to the total removal of the soil bensulfuron-methyl. Within the dosage range set in this study, the root development of ryegrass was not adversely affected by the presence of the soil bensulfuron-methyl although the fresh biomass of shoot was slightly reduced in the higher dosage treatments. This can be attributed to the adsorption of the added bensulfuron-methyl by soil colloids and consequently the reduction of bensulfuron-methyl level in the soil pore water to a concentration sufficiently lower than the toxic level. The growth of ryegrass significantly increased soil pH and the activities of phosphatase and peroxidase but reduced the EC and the activities of urease in the rhizospheric soil.

Dual drive acute lethal toxicity of methylene blue to Daphnia magna by polystyrene microplastics and light.

Microplastics (MPs) can adsorb and influence the toxicity of traditional pollutants significantly. Although the complex toxicity of MPs and molecular pollutants were frequently reported, rare work has been done on the influence of MPs on the phototoxicity of photosensitive pollutants under light illumination condition. Herein, polystyrene microplastics (PS) (~1 µm in diameter, 5.0 mg/L) was used as a model MP to investigate its influence on the phototoxicity of a soluble blue dye, methylene blue (MB) using Daphnia magna as a model organism. The results indicate that PS could adsorb MB effectively and quickly, thus led to concentrated MB on PS/water interface. D. magna ingested MB-adsorbed PS very quickly within tens of minutes. Although MB or PS alone led to negligible lethal phototoxicity to D. magna, PS significantly enhanced the lethal phototoxicity of MB (0.25 mg/L) to D. magna after light illumination (10 h) with the survival rate decreased by 63.3 % compared with the control in the dark. Further, the phototoxicity of MB was found positively consistent with PS concentration from 0.50 mg/L to 7.50 mg/L. The singlet oxygen fluorescence assay indicates that the presence of PS did not increase the total amount of singlet oxygen in the aquatic environment but increased the local concentration in the gut area via non-selective ingestion of D. magna. High level singlet oxygen generated in the gut might possibly be the main reason that led to the massive death of D. magna. Surface adsorption of photosensitive pollutants may transform inert MPs into persistent solid sources of singlet oxygen production and become a new potential lethal threat to aquatic small organisms and ecological equilibrium. This kind of MPs and light dual drive phototoxicity of photosensitive pollutants needs to paid more attention in understanding the uncertain ecological risk of MPs.

Combined effects of perchlorate and hexavalent chromium on the survival, growth and reproduction of Daphnia carinata.

Perchlorate and hexavalent chromium (Cr(VI)) are common cocontaminants in aquatic environments due to their high water solubility, stability, mobility, and some coapplications. However, few studies have investigated their combined toxicity to organisms. In this work, we studied the acute and chronic toxicities of perchlorate and Cr(VI), alone and in combination, with survival, growth, and reproduction as endpoints using Daphnia carinata as a model organism. For a single contaminant, Cr(VI) was found to be more toxic than perchlorate to D. carinata not only in terms of survival but also in terms of growth and reproduction. In regard to the combined pattern, the interactive effects on survival, growth, and reproduction were mainly additivity, antagonism, and synergism, respectively, suggesting that the interactive response of perchlorate and Cr(VI) is endpoint-specific. Due to significant synergism, over 21 days of observation, the inhibition of 0.1 mg/L perchlorate and 0.2 mg/L Cr(VI) on cumulative offspring per female in the first seven broods reached 63.9 ± 3.6%, suggesting that long-term exposure to perchlorate and Cr(VI) at environmentally relevant concentrations may affect D. carinata reproduction in the natural environment. Our results will be significant for understanding the complicated combined toxicity of perchlorate and Cr to aquatic organisms.

The migration of cadmium and lead in soil columns and their bioaccumulation in a multi-species soil system.

A soil microcosm experiment was carried out to quantify the transfer of cadmium (Cd) and lead (Pb) in a multi-species soil system (MS·3). Red earth from Jiangxi (S1), fluvo-aquic soil from Henan (S2), fluvo-aquic soil from Beijing (S3), and black soil from Heilongjiang (S4) were used for soil column packing with S1, S3, or S4 as the 20-50 cm layer and S2, which was Cd- and Pb-contaminated, as the top 0-20 cm layer. For each soil combination, four treatments were set up: CK (no wheat and no earthworm), W (only wheat), E (only earthworm), and E + W (earthworm and wheat). The results showed that the coexistence of earthworm with wheat reduced Cd and Pb contents in wheat plants and earthworms, and increased plant biomass, but had no significant effect on the survival rate and mean weight change rate of earthworms. Total Cd and Pb decreased remarkably in the 0-20 cm layer while increased in the 20-50 cm layer, and approximately 32.8%-51.1% of Cd and 0.35%-7.0% of Pb migrated down into the 20-50 cm soil layers from the 0-20 cm soil layers. The migration varied between the treatments from S2 to S1, S2, and S3. In S2-S1 and S2-S4 columns, the amount of Cd migration decreased when the earthworms coexisted with wheat, while in S2-S3 column, there was no significant difference on such amount regardless of the coexistence of earthworms with wheat. Taken together, the results indicated that the migration of Cd and Pb was not only associated with wheat and earthworm, but also depended on soil types.

Effects of biochar and crop straws on the bioavailability of cadmium in contaminated soil.

Numerous studies have been investigated the potential of biochar (BC) derived from various materials and crop straw (CS) to decrease the bioavailability of heavy metals in soil contaminated with cadmium (Cd), and thereby reduce their potential risk to human health and the ecological environment. However, little attention has been given to the comparison of heavy metal remediation efficiency using BC and CS such as peanut vine (PV) and rice straw (RS), especially in soil contaminated with Cd. Here, we explore if Cd bioavailability is affected in contaminated soil by BC and CS. Peanuts were grown in plastic pots, which contained BC or CS at 5% (dry weight, w/w) in controlled environment mesocosms. The bioavailability of Cd in contaminated soil was measured by Cd concentration in the plant and the concentrations of various forms of Cd in the soil. At the same plant age, growth with BC (compared with PV and RS) led to 13.56% and 8.28% lower rates of Cd content in the aboveground parts, 40.65% and 35.67% lower rates of Cd content in the seeds, yet 9.08% and 7.09% lower rates of Cd content in the roots, yet 35.80% and 28.48% lower rates of exchangeable Cd content in the soil. Moreover, BC amendment enhanced the biomass of peanut and physiological quality. Thus, BC had a greater impact on immobilizing Cd in the soil. The results imply that BC was more significantly (P < 0.05) remarkable in decreasing the Cd bioavailability and improving the biomass of peanut. BC has greater potential for enhancing soil quality and promoting peanut growth. In conclusion, this research demonstrates an understanding of employing BC as a promising inexpensive and eco-friendly amendment to remediate soil contaminated with Cd.

The compound effects of biochar and iron on watercress in a Cd/Pb-contaminated soil.

Pot experiment was conducted to evaluate the effect of two types of biochar (2% (w/w)), Pennisetum sinese Roxb biochar (PB) and coffee grounds biochar (CB), combined with iron fertilizer (1.3 g kg-1 Fe) on the growth, quality, Cd/Pb accumulation in watercress, soil physicochemical properties, soil fertility, soil enzyme activities, and fraction distribution of Cd/Pb in soil. The results showed that the two types of biochar combined with iron fertilizer (BC-Fe) amendments could increase the shoot height, root length, plant biomass, soluble sugar and soluble protein of watercress, soil pH value, soil organic matter (SOM), ammonium nitrogen (NH4+-N), available phosphorus, and available potassium. CB-Fe amendment enhanced soil urease, sucrose, and catalase activities, while PB-Fe amendment only enhanced soil urease activity among the three enzymes. The two BC-Fe amendments decreased exchangeable-Cd/Pb and reducible-Cd/Pb concentrations, while enhanced oxidizable-Cd/Pb and residual-Cd/Pb concentrations. Furthermore, the two BC-Fe amendments decreased significantly Cd and Pb accumulation in watercress root and shoot. The reduction rate for Cd and Pb in shoot by 42.9%, 20.0%, and 68.2%, 58.4% under PB-Fe and by 38.1%, 20%, and 62.5%, 48.8% under CB-Fe, respectively, for the first crop and the second crop. In conclusion, BC-Fe amendment could improve soil physicochemical properties and soil fertility, promote Cd and Pb transfer to the stable form, thus, reduce the bioavailability and mobility of Cd and Pb, and further, decrease Cd and Pb ecotoxicity and its accumulation in watercress and improve watercress quality.

Soil properties and cultivars determine heavy metal accumulation in rice grain and cultivars respond differently to Cd stress.

Field and pot experiments were conducted to evaluate the factors affecting heavy metal (HM) accumulation in rice grain and subsequently to explore their cultivar difference when exposed to Cd. Forty-seven paired soil and rice cultivar samples were collected from Jiangxi province, China. The contents of Cd, Cu, Zn, Pb, Cr, and Ni in soils and grains were determined. It showed that among these metals, Cr and Cd were the dominant contaminants in samples from the test areas, with 100.0% and 59.6% of all grain samples exceeding the maximum permissible concentration. Random forest analysis showed that soil pH, soil organic matter (SOM), Fe fraction and cultivar were four most important factors affecting HMs accumulation in grain. Based on bioconcentration factors, two cultivars with high Cd (HCd) accumulation ability and two cultivars with low Cd (LCd) accumulation ability in rice grain were chosen to explore their physiological and growth responses when exposed to 0, 50, 100 and 1000 µmol L-1 Cd. The results showed that the Cd phytotoxicity is Cd level- and cultivar-dependent. The height and weight decreased, while Cd accumulation increased in shoot and root for the four rice cultivars with the increasing of Cd content. The HCd cultivars showed less membrane damage, higher superoxide dismutase (SOD) activity and higher Cd accumulation than that of LCd cultivars. In conclusion, heavy metal accumulation in rice grain is soil property- and cultivar-dependent. And different rice cultivars respond differently to Cd stress.

In situ immobilisation of toxic metals in soil using Maifan stone and illite/smectite clay.

Clay minerals have been proposed as amendments for remediating metal-contaminated soils owing to their abundant reserves, high performance, simplicity of use and low cost. Two novel clay minerals, Maifan stone and illite/smectite clay, were examined in the in situ immobilisation of soil metals. The application of 0.5% Maifan stone or illite/smectite clay to field soils significantly decreased the fractions of diethylenetriaminepentaacetic acid (DTPA)-extractable Cd, Ni, Cr, Zn, Cu and Pb. Furthermore, reductions of 35.4% and 7.0% in the DTPA-extractable fraction of Cd were obtained with the Maifan stone and illite/smectite clay treatments, respectively, which also significantly reduced the uptake of Cd, Ni, Cr, Zn, Cu and Pb in the edible parts of Brassica rapa subspecies pekinensis, Brassica campestris and Spinacia oleracea. Quantitatively, the Maifan stone treatment reduced the metal uptake in B. rapa ssp. Pekinensis, B. campestris and S. oleracea from 11.6% to 62.2%, 4.6% to 41.8% and 11.3% to 58.2%, respectively, whereas illite/smectite clay produced reductions of 8.5% to 62.8% and 4.2% to 37.6% in the metal uptake in B. rapa ssp. Pekinensis and B. campestris, respectively. Therefore, both Maifan stone and illite/smectite clay are promising amendments for contaminated soil remediation.

Effects of soil properties on copper toxicity to earthworm Eisenia fetida in 15 Chinese soils.

The bioavailability and toxicity of metals in soil are influenced by a variety of soil properties, and this principle should be recognized in establishing soil environmental quality criteria. In the present study, the uptake and toxicity of Cu to the earthworm Eisenia fetida in 15 Chinese soils with various soil properties were investigated, and regression models for predicting Cu toxicity across soils were developed. The results showed that earthworm survival and body weight change were less sensitive to Cu than earthworm cocoon production. The soil Cu-based median effective concentrations (EC50s) for earthworm cocoon production varied from 27.7 to 383.7 mg kg(-1) among 15 Chinese soils, representing approximately 14-fold variation. Soil cation exchange capacity and organic carbon content were identified as key factors controlling Cu toxicity to earthworm cocoon production, and simple and multiple regression models were developed for predicting Cu toxicity across soils. Tissue Cu-based EC50s for earthworm cocoon production were also calculated and varied from 15.5 to 62.5 mg kg(-1) (4-fold variation). Compared to the soil Cu-based EC50s for cocoon production, the tissue Cu-based EC50s had less variation among soils, indicating that metals in tissue were more relevant to toxicity than metals in soil and hence represented better measurements of bioavailability.

Varietal differences in the growth of rice seedlings exposed to perchlorate and their antioxidative defense mechanisms.

A hydroponic experiment was conducted to investigate perchlorate (ClO4 (-) ) phytotoxicity in different rice varieties. Considerable variations were observed when 24 rice varieties were treated with ClO4 (-) . The shoot height, root length, and biomass of most varieties were significantly reduced by ClO4 (-) . The roots were more sensitive than the shoots. Hierarchical clustering analysis demonstrated primarily 4 groups: ClO4 (-) -sensitive, medium ClO4 (-) -sensitive, medium ClO4 (-) tolerant, and ClO4 (-) -tolerant. Gannuoxiang (a ClO4 (-) -tolerant variety) and IR65598-112-2 (a ClO4 (-) -sensitive variety) were chosen to explore their antioxidant response when exposed to 0.2 mmol/L, 2.0 mmol/L, and 4.0 mmol/L ClO4 (-) . The results showed that the activities of superoxide dismutase and catalase increased in the shoots and roots of gannuoxiang with increasing doses of ClO4 (-) , but both of them decreased at higher concentrations of ClO4 (-) in IR65598-112-2. The addition of ClO4 (-) led to a significant increase in peroxidase activities for both of the varieties, whereas the increase was more pronounced in gannuoxiang than in IR65598-112-2. No significant difference was found in malondialdehyde (MDA) contents in gannuoxiang, whereas the addition of ClO4 (-) increased the MDA level significantly in IR65598-112-2. The results indicated that gannuoxiang has higher activities of antioxidant enzymes than IR65598-112-2 to cope with oxidative damage caused by ClO4 (-) stress, which may be the main cause of its high tolerance.

Effects of perchlorate on growth of four wetland plants and its accumulation in plant tissues.

Perchlorate contamination in water is of concern because of uncertainties about toxicity and health effects, impact on ecosystems, and possible indirect exposure pathways to humans. Therefore, it is very important to investigate the ecotoxicology of perchlorate and to screen plant species for phytoremediation. Effects of perchlorate (20, 200, and 500 mg/L) on the growth of four wetland plants (Eichhornia crassipes, Acorus calamus L., Thalia dealbata, and Canna indica) as well as its accumulation in different plant tissues were investigated through water culture experiments. Twenty milligrams per liter of perchlorate had no significant effects on height, root length, aboveground part weight, root weight, and oxidizing power of roots of four plants, except A. calamus, and increasing concentrations of perchlorate showed that out of the four wetland plants, only A. calamus had a significant (p<0.05) dose-dependent decrease in these parameters. When treated with 500 mg/L perchlorate, these parameters and chlorophyll content in the leaf of plants showed significant decline contrasted to control groups, except the root length of E. crassipes and C. indica. The order of inhibition rates of perchlorate on root length, aboveground part weight and root weight, and oxidizing power of roots was: A. calamus > C. indica > T. dealbata > E. crassipes and on chlorophyll content in the leaf it was: A. calamus > T. dealbata > C. indica > E. crassipes. The higher the concentration of perchlorate used, the higher the amount of perchlorate accumulation in plants. Perchlorate accumulation in aboveground tissues was much higher than that in underground tissues and leaf was the main tissue for perchlorate accumulation. The order of perchlorate accumulation content and the bioconcentration factor in leaf of four plants was: E. crassipes > C. indica > T. dealbata > A. calamus. Therefore, E. crassipes might be an ideal plant with high tolerance ability and accumulation ability for constructing wetland to remediate high levels of perchlorate polluted water.