Effect of pH on the acute toxicity of hexavalent chromium to rainbow trout (Salmo gairdneri)

The acute toxicity of hexavalent chromium, Cr(VI). to rainbow trout (Salmo gairdneri) increased with decreasing pH in the range from 7.8 to 6.5. Morphological changes that could be associated with acute Cr(VI) poisoning at pH 7.8 were found in gills, kidney and stomach, whereas those at pH 6.5 appeared to be restricted to the gills only. At both pH values, however, similar alterations in plasma osmolality and hematocrit values of blood were found in fish surviving an exposure to acute toxic concentrations.To explain the observed effects, hydroehromate (HCrO₄^?) and chromate (CrO^2?₄) were considered as the toxic species of Cr(VI). An attempt was made to calculate the relative toxicities of these ionic species from empirical toxicity relationships for weak acids in fish, as described in the literature.     

Modification of the acute toxic response of Daphnia magna Straus 1820 to Cr(VI) by the effect of varying saline concentrations (NaCl)

Daphnia magna Straus is a freshwater organism that can strive in environments with a salinity of up to 12 psu, although its life cycle and survival are significantly affected by increasing salinities. Saline environments are not devoid of chemical contaminant influences, such as toxic metals; for freshwater species this could be another stress factor aside from that caused by salinity. In this study, we assessed the acute (48 h) toxicity produced by hexavalent chromium [Cr(VI)] in neonates of a D. magna strain previously acclimated to different salinities induced by adding NaCl to reconstituted hard water. The Mean Lethal Concentration (CL₅₀) values determined for Cr(VI) were 0.14 ± 0.12, 1.35 ± 0.34, 1.79 ± 0.41, 2.0 ± 0.21, 2.02 ± 0.075, and 2.6 ± 0.23 mg l⁻¹ for salinities of 0.3, 1, 2, 3, 4, and 5 psu, respectively, evidencing that D. magna’s sensitivity to Cr(VI) decreased with increasing salinity. The increase in tolerance could be due to a possible antagonic effect of NaCl on Cr(VI) rather than due to a reduction in Cr(VI) bioavailability due to the NaCl concentration. Although it was not demonstrated that the stress produced by salinity increased the sensitivity to the exposed toxicant, care must be exerted in inferring that the impact of contaminants, such as toxic metals, could be lower on freshwater species that sporadically or permanently strive in brackish water environments.     

Effect of Varying Physicochemistry of European Surface Waters on the Copper Toxicity to the Green Alga <Emphasis Type="Italic">Pseudokirchneriella subcapitata</Emphasis>

Most standard toxicity test results, used in present environmental risk assessment and water quality criteria (WQC) setting procedures are obtained with standard test media that are not representative for natural surface waters when metal toxicity modifying factors like pH, water hardness and dissolved organic carbon (DOC) are considered. The aim of this study was, using the green alga Pseudokirchneriella subcapitata, (1) to investigate the individual effects of Ca, Mg (the hardness cations) and pH on the toxicity of copper in reconstituted artificial test waters and (2) to study the copper toxicity in 13 spiked surface waters originating from different European eco-regions. Surface waters were selected such that a broad range of DOC (1.55–20.4 mg/l), pH (5.52–8.30) and water hardness (7–238 mg CaCO₃/l) was covered. Tests in reconstituted artificial waters demonstrated that the 72 h-E_bC50 (expressed as dissolved Cu) increased by about a factor of 3 when the Ca and Mg concentrations increased from 0.25 to 2.5 mM. When pH was increased from 5.8 to 8.0, dissolved 72 h-E_bC50 decreased by a factor of 3. It is suggested that competition between Cu²⁺, Ca²⁺, Mg²⁺ and H⁺ ions at the cell surface are the most likely explanation for these observations. Dissolved 72 h-E_bC50s in the natural surface waters varied between 32.0 and 245 μg Cu/l and were up to a factor 15 higher than the 72 h-E_bC50 in standard artificial medium (16.5±4.8 μg Cu/l). Consequently, Water Effect Ratio’s (WER, the ratio between the EC50 in natural water to the EC50 in standard test water) ranged from 1.9 to 14.8. Linear regression analysis revealed that higher E_bC50 were significantly related to higher DOC-concentration of the natural waters (R ² = 0.69), but that water hardness and pH did not show a significant relation with copper toxicity in these surface waters. In European surface waters, a positive correlation is observed between water hardness and pH. As a result, hardness and pH effects on copper toxicity are counteractive in European surface waters, resulting in the highly significant relation between the 72 h-E_bC50 and DOC-concentration. Normalisation of the obtained effect concentrations using a Biotic Ligand based predictive Cu-toxicity model revealed that variation in DOC and pH are mainly responsible for the observed differences of Cu-toxicity in natural waters.     

Evaluating the ameliorative effect of natural dissolved organic matter (DOM) quality on copper toxicity to Daphnia magna: improving the BLM

Various quality predictors of seven different natural dissolved organic matter (DOM) and humic substances were evaluated for their influence on protection of Daphnia magna neonates against copper (Cu) toxicity. Protection was examined at 3 and 6 mg l⁻¹ of dissolved organic carbon (DOC) of each DOM isolate added to moderately hard, dechlorinated water. Other water chemistry parameters (pH, concentrations of DOC, calcium, magnesium and sodium) were kept relatively constant. Predictors included absorbance ratios Abs_254/365 (index of molecular weight) and Abs-octanol₂₅₄/Abs-water₂₅₄ (index of lipophilicity), specific absorption coefficient (SAC₃₄₀; index of aromaticity), and fluorescence index (FI; index of source). In addition, the fluorescent components (humic-like, fulvic-like, tryptophan-like, and tyrosine-like) of the isolates were quantified by parallel factor analysis (PARAFAC). Up to 4-fold source-dependent differences in protection were observed amongst the different DOMs. Significant correlations in toxicity amelioration were found with Abs_254/365, Abs-octanol₂₅₄/Abs-water₂₅₄, SAC₃₄₀, and with the humic-like fluorescent component. The relationships with FI were not significant and there were no relationships with the tryptophan-like or tyrosine-like fluorescent components at 3 mg C l⁻¹, whereas a negative correlation was seen with the fulvic-like component. In general, the results indicate that larger, optically dark, more lipophilic, more aromatic DOMs of terrigenous origin, with higher humic-like content, are more protective against Cu toxicity. A method for incorporating SAC₃₄₀ as a DOM quality indicator into the Biotic Ligand Model is presented; this may increase the accuracy for predicting Cu toxicity in natural waters.     

Multilaboratory evaluation of 15 bioassays for (eco)toxicity screening and hazard ranking of engineered nanomaterials: FP7 project NANOVALID

Within EU FP7 project NANOVALID, the (eco)toxicity of 7 well-characterized engineered nanomaterials (NMs) was evaluated by 15 bioassays in 4 laboratories. The highest tested nominal concentration of NMs was 100?mg/l. The panel of the bioassays yielded the following toxicity order: Ag?>?ZnO?>?CuO?>?TiO_2?>_?MWCNTs?>?SiO_2?>_?Au. Ag, ZnO and CuO proved very toxic in the majority of assays, assumingly due to dissolution. The latter was supported by the parallel analysis of the toxicity of respective soluble metal salts. The most sensitive tests/species were Daphnia magna (towards Ag NMs, 24-h EC_50?=_?0.003?mg Ag/l), algae Raphidocelis subcapitata (ZnO and CuO, 72-h EC_50?=_?0.14?mg Zn/l and 0.7?mg Cu/l, respectively) and murine fibroblasts BALB/3T3 (CuO, 48-h EC_50?=_?0.7?mg Cu/l). MWCNTs showed toxicity only towards rat alveolar macrophages (EC_50?=_?15.3?mg/l) assumingly due to high aspect ratio and TiO₂ towards R. subcapitata (EC_50?=_?6.8?mg Ti/l) due to agglomeration of TiO₂ and entrapment of algal cells. Finally, we constructed a decision tree to select the bioassays for hazard ranking of NMs. For NM testing, we recommend a multitrophic suite of 4 in vitro (eco)toxicity assays: 48-h D. magna immobilization (OECD202), 72-h R. subcapitata growth inhibition (OECD201), 30-min Vibrio fischeri bioluminescence inhibition (ISO2010) and 48-h murine fibroblast BALB/3T3 neutral red uptake in vitro (OECD129) representing crustaceans, algae, bacteria and mammalian cells, respectively. Notably, our results showed that these assays, standardized for toxicity evaluation of “regular” chemicals, proved efficient also for shortlisting of hazardous NMs. Additional assays are recommended for immunotoxicity evaluation of high aspect ratio NMs (such as MWCNTs).     

Comparative histological studies on liver of mice exposed to Cr(VI) and Cr(V) compounds

Chromium toxicity is strongly dependent on its oxidation state. Cr(VI) is carcinogenic and mutagenic, although its in vivo and in vitro toxic effects are related to its intracellular fate. Inside the cells, Cr(VI) is rapidly reduced to stable Cr(III). As Cr(V) and Cr(IV) species have been reported to be formed in the Cr(VI) reduction pathways, Cr(VI)-induced damage is thought, at least in part, to arise from these hypervalent species. The study of Cr(VI) reduction mechanisms and the characterization of the effects of each reactive intermediate constitute important steps towards a better understanding of chromium toxicity. The purpose of this work is to enlarge the scope of Cr(VI)-induced alterations in mouse to other chromium species. Our studies have led to the in situ preparation of a new Cr(V) complex, 1Cr(V)-BT](2-), a stable compound at neutral pH, which mimics Cr(VI) reduction intermediates. The effect of Cr(V) on the histology of mice liver is assessed and compared with similar Cr(VI) assays. Liver toxicity was examined after single administrations of Cr(VI) or [Cr(V)-BT](2-) to mice. Both compounds produced reversible hepatic damage in a time-dependent manner. However, Cr(V) toxic effects have proved to be more rapid than with Cr(VI), permitting the role of Cr(VI) intermediates formed during intracellular chromium reduction to be highlighted.     

Thiocyanate toxicity to Daphnia magna: modified by pH and temperature

The toxicity of thiocyanate to Daphnia magna was investigated under different conditions of pH (5, 6 and 7) and temperature (8, 12 and 16°C). Water hardness was kept constant at 75 mg/l. Results indicate that at all pH levels an increase in temperature from 8 to 16°C increased toxicity. A rise in temperature from 8 to 16°C at pH 7 showed the greatest increase in toxicity (10-fold); at pH 5, a similar increase in temperature resulted in a 5.5-fold increase in toxicity. At all temperatures tested, an increase in pH from 5 to 7 decreased toxicity. The most toxic combination was found at pH 5 at 16°C. There are two main conclusions to be found based on these data. (1) The currently proposed standard for thiocyanate in effluent is too high to safely maintain D. magna populations. (2) The parameters used, pH and temperature, are important modifying factors of thiocyanate toxicity.     

Ecotoxicity of losartan potassium in aquatic organisms of different trophic levels

The intensive use of the antihypertensive losartan potassium (LOS) has culminated in its high occurrence in aquatic environments. However, insufficient studies had investigated its effects in non-target organisms. In this study, ecotoxicity of LOS was assessed in aquatic organisms from distinct trophic levels (Desmodesmus subspicatus, Daphnia magna, and Astyanax altiparanae). Genotoxicity was assessed by the comet assay in D. magna and A. altiparanae, and biochemical biomarkers for the fish. LOS was more toxic to D. subspicatus (EC_50(72h) = 27.93 mg L⁻¹) than D. magna (EC₅₀ = 303.69 mg L⁻¹). Subsequently, this drug showed to induce more DNA damage in D. magna than A. altiparanae, when exposed to 2.5 mg L⁻¹. No significant stress responses were observed by the fish biomarkers, suggesting that higher trophic levels organisms are more tolerant to LOS toxicity. LOS showed relatively low toxic potential for a short period of exposure, but with different patterns of toxicity for the organisms from distinct trophic levels, contributing to further risk assessment of LOS.     

Toxic effects of Triclosan on the detoxification system and breeding of Daphnia magna

The toxic effects of different concentrations of Triclosan (TCS) (1–128 μg/L) on Daphnia magna (D. magna) were investigated by acute (48 h) and chronic (21-day) toxicity tests. The response of antioxidase system and Phase I metabolism process of D. magna exposed to TCS were investigated by measuring a series of biomarkers including glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), malondialdehyde (MDA), 7-ethoxyresorufin O-deethylase (EROD), Erythromycin N-demethylase (ERND) and Aminopyrine N-demethylase (APND). The 48 h LC₅₀ of TCS was 330 μg/L for D. magna. In the chronic test, total number of neonates per female, body length and the intrinsic rate of natural increase (r) of D. magna increased at the low exposure concentrations (1–16 μg/L) and decreased at the high concentrations (64–128 μg/L), while the total number of molting per adult decreased continually. The GST and CAT activities showed no significant increase in all treatments, and SOD activities were induced after 24-h exposure and inhibited after 48-h exposure at 4–128 μg/L of concentrations. The MDA content increased after 6-h exposure but decreased after 48-h exposure at 4–128 μg/L. EROD activities initially increased after 6-h exposure, but decreased after 24 and 48-h exposure, ERND and APND activities showed a similar temporal pattern among different treatments groups. SOD, MDA and APND were sensitive to TCS, thus they are suitable as potential biomarkers for the exposure to TCS.     

Use of the biotic ligand model to predict pulse-exposure toxicity of copper to fathead minnows (Pimephales promelas)

Concentrations of cationic metals (e.g., Ag, Cd, Cu, Ni, Pb, Zn) and other water quality parameters (e.g., pH, alkalinity, hardness, dissolved organic carbon (DOC) concentration) often cycle daily in surface waters, and the toxicity of the metals to aquatic organisms is altered by variations in those water quality parameters. Consequently, a method is needed to predict the LC50s (median lethal concentrations) of dissolved metals in temporally varying water quality. In this study, we combined the biotic ligand model (BLM), which predicts toxicity of cationic metals across a wide range of water quality conditions, with a one-compartment uptake-depuration (OCUD) model, which predicts toxicity of a chemical at any exposure time in either continuous or time-variable exposures, to test whether we could accurately predict pulse-exposure toxicity of Cu to fathead minnow (FHM; Pimephales promelas) larvae. First, we conducted continuous-exposure toxicity tests to calculate 1- to 96-h Cu LC50s for the FHM larvae. Then we re-parameterized the default Cu BLM for FHM until the corresponding predicted Cu LA50s (medial lethal accumulations at the biotic ligand) collapsed together into a narrow band and also fit the generalized pattern of an OCUD model [i.e., a steeply sloping plot of ln(LA50) versus ln(time) at short exposure times, followed by a gradual approach to an incipient lethal level at longer exposure times]. Next, in 72-h tests, we exposed FHM larvae to 2- or 8-h square-wave pulses of elevated Cu concentration followed by recovery in uncontaminated water for the remaining 22 or 16 h in each of three consecutive 24-h pulse-and-recovery cycles, at pH 6 or 7 in water containing either 0.5 or 2 mEq/L hardness and 0 or 20 mg DOC/L. Using the combined BLM-OCUD model developed from continuous-exposure data, we then predicted the Cu LA50s in the pulse-exposure tests and compared those LA50s to the observed pulse-exposure Cu LA50s. Although predicted pulse-exposure LA50s were within approximately 4x of the observed pulse-exposure LA50s, delayed deaths during the recovery phases of the exposures precluded more accurate predictions of pulse-exposure Cu LA50s and, as a consequence, of pulse-exposure dissolved Cu LC50s. We conclude that one global OCUD equation linked to a re-parameterized Cu BLM for FHM can be used to predict the acute toxicity of continuous and pulse exposures of Cu to FHM larvae across a range of water quality conditions; but to improve the accuracy of those predictions, a mechanism must be developed to account for delayed deaths.     

Oxygen and chromium transfer in perfused gills of rainbow trout (salmo gairdneri) exposed to hexavalent chromium at two different pH levels

An in vitro study was performed on uptake and transfer of hexavalent chromium, Cr(VI), in gills of rainbow trout (Salmo gairdneri). Gills were perfused according to the isolated head perfusion technique, and externally exposed to Na₂CrO₄ solutions containing ⁵¹CrO₄². Experiments were conducted at a concentration of 10 $\text{mg}\text{l}$ Cr and at pH values of 8.1 and 6.5. The results show that the transfer of chromium is directly coupled with the transfer of oxygen from the external solution to the internal perfusion medium. Under similar conditions of oxygen transfer, however, chromium transfer was significantly more effective at pH 6.5 than at pH 8.1. In addition more chromium was accumulated by the gill tissue at the lower pH. Gill preparations of trout which had been pre-exposed in vivo for 4 days to 10 $\text{mg}\text{l}$ Cr(VI) at pH 6,5, exhibited an impaired oxygen transfer. This could be well explained by the structural alterations seen after histological examination of the perfused gills.     

Chemical composition and toxicity of waste dump leachates using Selenastrum capricornutum Printz (Chlorococcales,Chlorophyta)

Chemical composition and toxicity of leachates from a municipal waste dump in Buenos Aires Province were analyzed. Three sets of samples, obtained in 1996 and 1997, were compared. Levels of nitrogen, phosphorus, and organics (expressed as COD) were distinctly lower in 1997. Such differences were mainly attributed to higher rainfall in that year. The Selenastrum capricornutum assay showed a high sensitivity to heavy metals (Cd=0.049 mg L⁻¹; Cr hexavalent=0.247 mg L⁻¹ and Zn=0.037 mg L⁻¹). Cu, Zn, and Pb concentrations were toxic to algae in leachate samples of the first year, while the EC₅₀ leachates were slightly toxic (86.6 and 99.31%). Most likely, high levels of organics (COD=4640 and 3470 mg L⁻¹) form complex mixtures with metals reducing their toxicity. The EC₅₀ leachate=48.5% in the last year may be explained by high concentrations of Pb and Cu. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 76–80, 2000     

Ecotoxicity and Environmental Risk Assessment of Larvicides Used in the Control of Aedes aegypti to Daphnia magna (Crustacea,Cladocera)

Dengue transmitted by mosquitoes of the genus Aedes, species aegypti, is a major public health concern in Brazil. The chemical control of the mosquito larvae has been performed with the larvicide temephos since 1967. However, vector resistance was reported to temephos in several Brazilian states, and the Ministry of Health ordered the replacement of this larvicide by diflubenzuron (DFB), an inhibitor of chitin synthesis. Both insecticides are diluted in water with larvae and are able to reach aquatic environments in which they subsequently adversely damage nontarget organisms. The aims of this study were to (1) determine the acute toxicity (EC50) and environmental risk (RQ) of DFB and temephos to the microcrustacean Daphnia magna, and (2) evaluate the chronic toxicity (no-observed-effect concentration [NOEC] and lowest-observed-effect concentration [LOEC]) of these larvicides to D. magna. The experiments were performed according to a completely randomized design. The estimated 48-h EC₅₀ of temephos was 0.15 μg/L (lower limit = 0.1 and upper limit = 0.2 μg/L) and the 48-h EC₅₀ of DFB was 0.06 μg/L (lower limit = 0.03 and upper limit = 0.1 μg/L). RQ values were 4.166.7 to DFB and 6.666.6 to temephos. NOEC and LOEC values were respectively 2.5 and 5 ng/L for DFB, and respectively 6.2 and 12.5 ng/L for temephos. Thus, temephos and DFB are classified as highly toxic to Daphnia magna and pose a high environmental risk to this species. Mortality of D. magna was observed at concentrations lower than those used in the field to control A. aegypti larvae.     

Evaluation of the toxic and genotoxic potential of acid mine drainage using physicochemical parameters and bioassays

Carboniferous activity generates acid mine drainage (AMD) which is capable of unleashing toxic effects on the exposed biota. The aim of this study was to evaluate the toxic and genotoxic potential of untreated-AMD and AMD treated with calcinated sediment, using physicochemical parameters and bioassays. Results revealed that untreated-AMD presented low pH values and elevated concentrations of the metals Fe, Al, Mn, Zn and Cu. High acute toxicity was observed in Artemia sp. and Daphnia magna, and sub-chronic toxicity and genotoxicity in Allium cepa L. as well as scission of plasmid DNA exposed to untreated-AMD. Treatment of AMD with calcinated sediment promoted the reduction of acidity and the removal of metals, as well as a reduction in toxic and genotoxic effects. In conclusion, the calcinated sediment can be used as an alternative AMD treatment.     

A Ca2+ chelator ameliorates chromium (VI)-induced hepatocyte L-02 injury via down-regulation of voltage-Dependent anion channel 1 (VDAC1) expression

Hexavalent chromium could result in cell malfunctions. Intracellular Ca²⁺ ([Ca²⁺]_i) content and VDAC1 expression are both important features related to cell survial. This study aimed to explore the mechanism of cell injury induced by Cr(VI) and tentatively offer clues to repairing this cell damage using [Ca²⁺]_i and VDAC1. L-02 hepatocytes were treated with Cr(VI)/BAPTA, and the levels of [Ca²⁺]_i and cell injury associated with Cr(VI) were determined in addition to the effect of BAPTA. The expression of VDAC1 in Cr(VI)-induced cells was evaluated. The results showed a dose-dependent elevation of the level of VDAC1 and the mRNA level of the VDAC1 biogenesis-related gene Sam50. BAPTA could ameliorate less severe damage induced by 4 μM Cr(VI) via reducing VDAC1 and Sam50. Additionally, cell injury caused by less than 4 μM Cr(VI) could be ameliorated by VDAC1 knockdown. Taken together, the findings of this study suggest that inhibition of intracellular Ca^2± overload could protect cells from damage and that VDAC1 plays a considerable role in Cr(VI)-induced liver injury.     

Acute toxicity of 50 metals to Daphnia magna

Metals are essential for human life and physiological functions but may sometimes cause disorders. Therefore, we conducted acute toxicity testing of 50 metals in Daphnia magna: EC50s of seven elements (Be, Cu, Ag, Cd, Os, Au and Hg) were < 100 µg l^?1; EC50s of 13 elements (Al, Sc, Cr, Co, Ni, Zn, Se, Rb, Y, Rh, Pt, Tl and Pb) were between 100 and 1000 µg l^?1; EC50s of 14 elements (Li, V, Mn, Fe, Ge, As, In, Sn, Sb, Te, Cs, Ba, W and Ir) were between 1,001 and 100,000 µg l^?1; EC50s of six elements (Na, Mg, K, Ca, Sr and Mo) were > 100,000 µg l^?1; and. 7 elements (Ti, Zr, Bi, Nb, Hf, Re and Ta) did not show EC50 at the upper limit of respective aqueous solubility, and EC50s were not obtained. Ga, Ru and Pd adhered to the body of D. magna and physically retarded the movement of D. magna. These metals formed hydroxides after adjusting the pH. Therefore, here, we distinguished this physical effect from the physiological toxic effect. The acute toxicity results of 40 elements obtained in this study were not correlated with electronegativity. Similarly, the acute toxicity results of metals including the rare metals were also not correlated with first ionization energy, atomic weight, atomic number, covalent radius, atomic radius or ionic radius. Copyright © 2014 John Wiley & Sons, Ltd.     

Differentiation of the toxicities of silver nanoparticles and silver ions to the Japanese medaka (Oryzias latipes) and the cladoceran Daphnia magna

Abstract

Silver nanoparticles (AgNPs) are increasingly used in various fields. However, little is known about the environmental effects of widespread use of products containing AgNPs. The objective of this study was to determine the ecotoxicity caused by AgNPs. The 48-h effective concentration 50 (EC₅₀) values for Daphnia magna of suspensions of 60 nm and 300 nm AgNPs were 1.0 (95% confidence interval [CI] = 0.1–1.3) and 1.4 (95% CI = 0.3–2.1) μg Ag/l, respectively. The 96 h LC₅₀ values for Oryzias latipes of 60 nm and 300 nm AgNP suspensions were 28 (95% CI = 23–34) and 67 (95% CI = 45–108) μg Ag/l, respectively. To show that toxicity is caused only by Ag⁺ and not by AgNPs, Ag⁺ was adsorbed onto the synthesized sorbents packed in a column and D. magna was exposed to the column-passed-300 nm AgNP suspensions. There was no acute toxicity with the AgNP suspensions not containing Ag⁺.     

Canadian water quality guidelines for chromium

Canadian Water Quality Guidelines (CWQG) are numerical or narrative limits that protect designated water uses. Development of CWQG is based on review of chromium's properties, uses, fate in the environment, ambient levels, accumulation in biota, and toxicity. Chromium's principal uses and entry into the environment include electroplating, production of paints and pigments, tanning, wood preservation, chromium chemicals production, metal smelting, and pulp and paper production. Concentrations of chromium in Canada range between 1 and 545,000 ng·m⁻³ in air, 0.001 and 0.165 mg·L⁻¹ in water, nondetectable and 31,000 mg·kg⁻¹ in sediments, 10 and 5000 mg·kg⁻¹ in soils, 0.006 and 18 mg·kg⁻¹ in plants, and 0.03 and 1.6 mg·kg⁻¹ in animals. In nature, trivalent chromium sorbs to various ligands and forms insoluble entities becoming unavailable for uptake by biota. Hexavalent chromium forms many soluble salts that can enter body membranes and induce a toxic response. Estimates of toxicity of hexavalent chromium to aquatic life range from 0.0006 mg·L⁻¹ (reduction in algal growth) to 1000 mg·L⁻¹ (decrease in rest time of Chironomus tentans). For trivalent chromium the toxicity ranges from 0.002 mg·L⁻¹ (reduction in filtering rate of Perna perna) to 937 mg·L⁻¹ (48-h LC₅₀ of Asellus aquaticus). Plants are affected by the concentrations of hexavalent chromium ranging from 0.16 mg·L⁻¹ (growth reduction in lettuce) to 75 mg·L⁻¹ (no effects in sweet orange). For trivalent chromium the toxicity ranges between 0.104 mg·L⁻¹ (reduction in root growth of oats) and 50 mg·L⁻¹ (stunted growth of corn and tomato). Terrestrial animals such as the beagle dog can be affected by concentrations exceeding 62.7 mg·L⁻¹ (Cr VI). Mice can tolerate 100 mg·L⁻¹ of hexavalent chromium. Trivalent chromium has adverse effects on rats and mice at 28.0 mg·L⁻¹. For freshwater life, guidelines of 0.001 (Cr VI; full) and 0.008 (Cr III; interim) mg·L⁻¹ are recommended. For marine life, guidelines of 0.001 (Cr VI; draft) and 0.05 (Cr III; interim) mg·L⁻¹ are recommended. Irrigation guidelines are set at 0.008 (Cr VI) and 0.005 (Cr III). A guideline of 0.05 mg·L⁻¹ is recommended for drinking and livestock waters. © 1997 by John Wiley & Sons, Inc. Environ Toxicol Water Qual 12: 123–183, 1997     

Efficient adsorption of chlorpheniramine and hexavalent chromium (Cr(VI)) from water system using agronomic waste material

In present study, we report Cornulaca-monacantha stem (CS) and its activated carbon (CS-AC) for the removal of Cr(VI) and chlorpheniramine (CP) from aqueous system. The chemical composition and surface characteristics of samples were investigated using instrumental techniques such as Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM) and energy dispersive X-ray (EDX). The surface area was determined by Brunauer-Emmett-Teller(BET) method. The BET surface area of CS-AC (288.67 m²/g) was found higher as compared to CS adsorbent (47.58 m²/g). The adsorption behavior of adsorbates was extremely dependent on the solutions pH. The maximum uptake for Cr(VI) and CP were observed at pH of 2.0 and 8.0, respectively. The equilibrium data adequately follow the Langmuir isotherm (R² = 0.98–0.99), suggesting the monolayer sorption of adsorbate molecules. Kinetic investigations indicated that sorption behavior of Cr(VI) follow the pseudo-second-order model. While in case of CP, both pseudo-second-order and Elovich model provides the higher value of regression coefficient (R²). This revealed the chemical adsorption of adsorbate molecules. Thermodynamic study indicated the feasible, spontaneous and endothermic sorption of adsorbate molecules. The regeneration study implies that adsorbent was efficiently recovered from Cr(VI) and CP under different desorbing agents.The CS-AC adsorbent was possess 89.19% and 88.45% uptake for Cr(VI) and CP after 5th cycles of desorption-adsorption, respectively. Finally, we summarize that prepared adsorbent (CS-AC) is highly proficient, versatile and cost-effectively explored for Cr(VI) and CP decontamination from water system.