Microbial transformation of thiocyanate

Thiocyanate is present in appreciable concentration in coal carbonization wastewater along with other toxicants like phenols, cyanide, sulphide and ammonia. This paper encompasses studies on biodegradation of thiocyanate by a microbial consortium obtained from a biological treatment plant receiving coal carbonization wastewater. Effects of secondary toxicants and growth stimulants on thiocyanate oxidation by the consortium, and thiocyanate transformation in actual and partially treated coal carbonization waste, have also been studied. Results indicate that the consortium can degrade thiocyanate up to 1400 mg litre(-1) in batch culture with 10 mg litre(-1) of initial inoculum within a period of 6 days. Phenol above 500 mg litre(-1) and cyanide at 10 mg litre(-1) completely inhibits thiocyanate oxidation. Sulphide at 32 mg litre(-1) and ammonia at 4000 mg litre(-1) at neutral pH prolongs thiocyanate oxidation from 3 to 6 days and from 4 to 7.5 days, respectively. These studies reveal that elimination of phenolics, their oxidized products, ammonia, cyanides and sulphides is a pre-requisite for effective thiocyanate removal from the waste by the consortium. Bacteria of the genera Pseudomonas and Bacillus dominate the consortium.     

Effects of long- and short-term exposure to carbaryl on survival, growth and reproduction of Daphnia ambigua

In laboratory experiments a cladoceran, Daphnia ambigua, was exposed for six instars to the insecticide carbaryl at five different concentrations (1, 2, 3, 4, 5 microg litre(-1)) or received short-term (10-h) exposure to 5 microg carbaryl litre(-1) at different life stages of the animal. In the long-term exposure experiments carbaryl at 1 microg litre(-1) did not have any detectable effects on the animals, whereas 2 microg litre(-1) reduced the survival, growth and reproduction of the animals, and higher concentrations killed all the animals examined before they grew to the fifth instar. These results indicate that the range of sublethal concentrations of carbaryl for D. ambigua is narrow. In the short-term exposure experiments the animals did not suffer any damage when they were exposed to the chemical during the egg stage. However, their growth and egg production were reduced when the short-term exposure was conducted during the life stages from the final embryo stage to the third instar. The effect was most marked when the animals were treated during the first instar, indicating that this is the stage when the animals are most sensitive to the chemical.     

Effects of herbicides on two submersed aquatic macrophytes, Potamogeton pectinatus L. and Myriophyllum sibiricum Komarov, in a prairie wetland

Clopyralid, picloram, 2,4-D and a mixture of 2,4-D plus picloram, (Tordon 202C) were added to the water of 1 m square enclosures in a prairie wetland in Saskatchewan, Canada to produce concentrations of 0.01 and 0.1 mg active ingredient litre(-1). Effects on the submersed macrophytes, Potamogeton pectinatus and Myriophyllum sibiricum, were monitored by taking repeated measurements of plant weight, flower and tuber production and inspecting for injuries at 30 and 60 days after application. Clopyralid did not inhibit weight gain (growth) in either species, but stimulated growth and flowering by M. sibiricum at 0.01 mg litre(-1) and tuber production by P. pectinatus at both rates. The low rate of 2,4-D stimulated flowering by M. sibiricum and tuber production by P. pectinatus, whereas the high rate inhibited growth of M. sibiricum and injured both species. Picloram did not affect growth of either species, but injured M. sibiricum at both concentrations and inhibited flowering at 0.1 mg litre(-1). Tordon 202C at 0.1 mg litre(-1) caused reduced growth and flowering in M. sibiricum and injured both species; 0.01 mg litre(-1) also injured M. sibiricum. Mortality resulted only from Tordon 202C and 2,4-D. Field data are lacking to assess the extent to which submerged macrophytes in prairie ponds are exposed to harmful concentrations of herbicide from aerial spraying, drift from ground application, runoff or wind erosion of soil.     

Acceleration of catalase and peroxidase activities in Lemna minor L. and Allium cepa L. in response to low levels of aquatic mercury

The purpose of this study was to assess certain physiological responses of Lemna minor L. (duckweed) and Allium cepa L. (onion) to aquatic mercury at low concentrations. Following a 96-h exposure of plants to nutrient medium contaminated with known levels of mercuric chloride (HgCl(2)), 0.001 to 4 mg litre(-1) (0.0007 to 2.95 mg Hg litre(-1)) or methyl mercuric chloride (MeHgCl(2)), 0.0001 to 0.1 mg litre(-1) (0.0007 to 0.07 mg Hg litre(-1)), the physiological endpoints measured were the growth of fronds (Lemna minor) or roots (Allium cepa), and catalase and peroxidase activities in both plant assays. The EC(50) for HgCl(2) on the basis of the growth curve of Lemna minor was found to be 2.1 mg litre(-1). HgCl(2) and MeHgCl(2) were lethal to L. minor at concentrations of 4 and 0.01 mg litre(-1), respectively. The range of low concentrations that accelerated growth as well as enzymic activities in L. minor was 0.004 to 0.04 mg litre(-1) for HgCl(2) and 0.001 mg litre(-1) for MeHgCl(2). HgCl(2) and MeHgCl(2) induced maximum enzymic activity in Lemna fronds at concentrations of 0.008 and 0.0005 mg litre(-1), respectively. In Allium roots, catalase activity was accelerated at all the concentrations of HgCl(2) (0.001-2 mg litre(-1)) and MeHgCl(2) (0.0001-0.1 mg litre(-1)) tested. The activity of peroxidase was, however, accelerated by HgCl(2) at concentration range 0.01-1.0 mg litre(-1), or by MeHgCl(2) at 0.001 mg litre(-1). The concentrations of HgCl(2) and MeHgCl(2) that induced the highest enzymic activity in Allium roots were 0.05 mg litre(-1) and 0.001 mg litre(-1), respectively.     

Dose-response studies with ethylenediurea (EDU) and radish

There is some concern that the antiozonant ethylenediurea (EDU), used for crop loss assessment due to ambient ozone (O3) may per se affect plant growth and yield. In view of this, and to provide knowledge for later field experiments, dose-response studies with EDU and O3 were carried out in greenhouses in winter and spring 1989, using radish (Raphanus sativus L.) cv. 'Cherry Belle' and 'Red Prince', grown in two different substrates. EDU was applied as a single or repeated soil drench in concentrations ranging from 300 to 800 mg litre(-1) in the first, and from 100 to 400 mg litre(-1) in the second trial. In the second experiment, plants were exposed to a chronic level of O3, mimicking ambient patterns, or to filtered air after the EDU-treatment. When applied in concentrations above 300 mg litre(-1), EDU reduced growth, thereby affecting the development of the thickened hypocotyl far more than the shoot growth that was partially stimulated by lower doses of EDU. Phytotoxic symptoms on the leaves, attributable to EDU, were observed at concentrations above 200 mg litre(-1), but complete protection from visible O3-injury was provided by a single application of EDU at a concentration as low as 100 mg litre(-1). Significant interactions on growth characters measured between O3-exposure and EDU application were observed only in one of the substrates. While these results demonstrate the need for careful dose-response studies prior to field assessments, they also provide evidence of a dosage that is effective in protecting radish from O3 damage without interfering with plant growth itself.     

The impact of inorganic tin on the planktonic cyanobacterium Synechocystis aquatilis: the effect of pH and humic acid

The influence of inorganic tin compounds on the unicellular cyanobacterium Synechocystis aquatilis was studied, and its dependence on changing pH of the surrounding medium and the presence of humic acid. Both Sn(II) and Sn(IV), used as chlorides (at the concentrations 1-10 mg litre(-1)), inhibit the growth and chlorophyll a content of the cyanobacterium cultures, but only under alkaline conditions. Generally, the observed tin toxicity increased with increase of metal concentration, time of exposure and pH value of the medium (in the range 7-9.8). Sn(II) seems to be more toxic than Sn(IV). At the lowest studied metal concentration (1 mg litre(-1)), Sn(II) caused a 36 and 40% decrease in growth and chl a content, respectively, after 96 h exposure at pH 9.8, while Sn(IV) caused even a slight increase of both physiological parameters (hormetic effect). Similar increases in growth and chl a content were also observed at a high Sn (II) and Sn(IV) concentration (10 mg litre(-1)), but only in cultures exposed to metal at pH 7. At high pH (9.8), 10 mg litre(-1) of Sn(II) and Sn(IV) significantly suppressed both the growth of the cyanobacterium (by 54.2 and 26.1%, respectively) and the chl a content in cultures (by 58.2 and 24%, respectively). Humic acid reduced the toxicity of tin towards the cyanobacterium. The observed effects of pH and complexing ligand on the inorganic tin toxicity are discussed in the context of changing, chemical metal speciation and bioavailability.     

Responses of bean (Phaseolus vulgaris L. cv. Pros) to chronic ozone exposure at two levels of atmospheric ammonia

Plants of bean (Phaseolus vulgaris cv. Pros) were exposed to a range of O3 concentrations up to 70 nl litre(-1) for 9 h day(-1) in the presence (45 nl litre(-1)) and absence (21 nl litre(-1)) of enhanced NH3 in 12 open-top chambers. Treatment effects on visible injury, growth and yield were assessed after 49 (intermediate harvest) and 62 days of exposure (final harvest). The proportion of leaves with visible injury at final harvest increased with increasing concentrations of O3. Enhanced NH3 did not cause any symptoms and did not affect injury by O3. The estimated seasonal mean concentration corresponding with 5% injury was circa 23 nl litre(-1) O3. Biomass production and green pod yield decreased with increasing concentrations of O3 and were generally stimulated by enhanced NH3 at both harvests. Adverse effects of O3 on biomass and pod yield did not depend on the NH3 level. Relative yield response to increasing 9-h daily mean O3 concentrations was nonlinear and yield losses of 5 and 10% were calculated to occur at seasonal daytime mean concentrations of 27 and 33 nl litre(-1) O3, respectively. Linear regression showed that the Accumulated exposures Over a Threshold of 30 (AOT30) and 40 nl litre(-1) (AOT40) O3 performed equally well. The estimated accumulated O3 exposures corresponding with a yield loss of 5% were 1600 nl litre(-1) h for AOT30 and 400 nl litre(-1) h for AOT40. The results are discussed in relation to the long-term critical level that is used as a guideline to protect crops against adverse effects by O3.     

Chronic effects of Cd on reproduction of Polypedilum nubifer (Chironomidae) through water and food

Chronic effects of Cd on reproduction of Polypedilum nubifer (Chironomidae) were investigated by Cd-exposure from the egg stage using a flow-through aquarium. No significant effect of Cd on reproduction was observed in the midge larvae which had been exposed to 10 or 20 microg Cd litre(-1). Emergence of the Cd-exposed larvae peaked several days before that of the control, although growth was impaired in 1st and/or 2nd instars. The percentage emergence success decreased to about 46% of the control at 40 microg Cd litre(-1). However, other reproductive processes (adult sex ratio, oviposition success and egg hatchability) were not impaired. The emergence success decreased to less than 3% of the control at 80 microg Cd litre(-1). The emergence success of midge larvae which had been fed Cd-contaminated food with 220 or 1800 microg Cd g(-1) decreased to nearly 60% of the control. However, other reproductive processes were not impaired. Emergence success of larvae exposed to food containing 22 microg Cd g(-1) was unaffected.     

Biological variation in sensitivity to N-heterocyclic PAHs; effects of acridine on seven species of micro-algae

The toxicity of the nitrogen (N) heterocyclic polyaromatic hydrocarbon (PAH) acridine was tested for seven species of microalgae: Scenedesmus acuminatus, Selenastrum capricornutum, Chlamydomonas eugametos, Staurastrum chaetoceras, Staurastrum manfeldtii, Navicula salinarum and Nitzschia sigma. The effect of acridine on the algae was studied in a 96-h growth test, in which growth rates were determined using cell numbers and biovolume. The obtained EC50 values (for growth rates based on cell numbers) ranged from 0.08 mg litre(-1) for N. sigma to 0.78 mg litre(-1) for C. eugametos and N. salinarum. Effect concentrations based on biovolume were slightly higher for most species. Metabolism of acridine was observed for one species (S. capricornutum), but this capacity did not result in a very different tolerance. Acridine toxicity was neither related to taxonomical background (green algae versus diatoms) nor to original habitat of the species (planktonic or benthic, eutrophic or oligo-mesotrophic). The presence of near-UV radiation during the incubation might explain the higher toxicity of acridine than is expected on basis of QSAR derived narcotic toxicity.     

Effects of the insect growth regulator (S)-methoprene on survival and reproduction of the freshwater cladoceran Moina macrocopa

This study examines the acute and chronic effects of the insecticide (S)-methoprene on the survival and reproduction of the freshwater cladoceran Moina macrocopa. In laboratory toxicity tests, the 24- and 48-h LC50 values for (S)-methoprene were 0.51 and 0.34 mg litre(-1), respectively. Survival, longevity and fecundity were reduced at 0.05 mg litre(-1) and higher concentrations. At 0.005 and 0.01 mg litre(-1), longevity and fecundity increased slightly as compared to control animals. If environmental concentrations of methoprene do not exceed 0.05 mg litre(-1), as is generally the case, application of this insecticide is unlikely to induce detrimental effects on natural cladoceran populations. The stimulatory effect of very low levels of methoprene on reproductive performance is consistent with the hypothesis of a regulatory role of juvenile hormone-like compounds in crustacean reproduction.     

Interactions between a polycyclic aromatic hydrocarbon mixture and the microbial communities in a natural freshwater sediment

The toxicity of a polycyclic aromatic hydrocarbon (PAH) mixture was assessed on the indigenous microbial communities of a natural freshwater sediment. The fate and effects of the PAH mixture (phenanthrene, fluoranthene and benzo(k)fluoranthene) were studied over 28 days. Bacterial communities were described by bacterial counts (total bacteria and viable bacteria), and by some hydrolytic enzyme activities (beta-glucosidase and leucine-aminopeptidase), PAH concentrations were measured in the overlying waters and in the sediments. No effect of PAH was detected at 30 mg/kg for all bacterial parameters. At 300 mg/kg, the quantity of total bacteria and the proportion of viable bacteria markedly decreased, compared to the control (0 mg PAH/kg). At 300 mg/kg, an increase of the beta-glucosidase activity and a decrease of the leucine-aminopeptidase activity were observed. For all treatments, the benzo(k)fluoranthene concentration in the sediment was stable over 28 days whereas, in the same time, only 3-6% of the initial concentrations of phenanthrene and fluoranthene remained. This study shows that (1) PAH induce perturbations of sediment microbial communities in terms of density and metabolism (but not always as an inhibition), (2) indigenous bacteria of sediments might be used for toxicity assessment of specific organic pollutants, (3) native microorganisms of sediment seem to have a high capacity for PAH degradation, depending on the physico-chemical properties and the bioavailability of the substance encountered.     

The effectiveness of lime-based amendments and bauxite residues at removing phosphorus from piggery effluent

Piggery effluent may contribute to the eutrophication of waterways, if it is not treated before disposal, because of high levels of phosphorus. Limes and red muds (a residue from bauxite refining) were used to remove phosphorus from piggery effluent (41 mg litre(-1) total P). Lime-based amendments were more effective than the red muds at removing phosphorus when compared at the same liquid: solid ratios. Based on laboratory data, the cost of treating effluent increased rapidly as the final required phosphorus concentration decreased to less than 4 mg litre(-1). Kiln dust was the cheapest amendment tested down to 2 mg litre(-1). Hydrated lime was able to clarify and flocculate the effluent to 1 mg litre(-1) within 60 min. The re-useability of all limes may be determined by a simple pH test. Red mud could be used to remove phosphorus when its pH was lowered to 6.0-6.5 and it is used at liquid:solid ratios <20:1.     

TNT and 4-amino-2,6-dinitrotoluene influence on germination and early seedling development of tall fescue

Cost-effective and environmentally acceptable methods are needed to remediate munitions-contaminated soil. Some perennial grass species are tolerant of soil contaminants and may promote remediation because of their high water use and extensive fibrous root systems. The effects of 2,4,6-trinitrotoluene (TNT) and its reduction product, 4-amino-2,6-dinitrotoluene (4ADNT), on germination and early seedling development of tall fescue (Festuca arundinacea Schreb.) were determined. Tall fescue seeds were germinated in nutrient-free agar containing 0-60 mg TNT litre(-1) or 0-15 mg 4ADNT litre(-1). Germination decreased linearly as TNT concentration increased but was not significantly affected by 4ADNT at these concentrations. Concentrations less than 30 mg TNT litre(-1) or 7.5 mg 4ADNT litre(-1) had little effect on seedling growth and development. Higher TNT or 4ADNT concentrations substantially delayed seedling development, caused abnormal radicle tissue development, and reduced secondary root and shoot growth. Seedling respiration rates decreased linearly with increasing TNT concentration. Experiments indicate that tall fescue may be grown in soils that maintain soil solution concentrations of 30 mg TNT litre(-1) or less.     

Metal bioaccumulation and metallothionein concentrations in larvae of Crassostrea gigas

Larval stages of bivalve molluscs are highly sensitive to pollutants. Oysters from a hatchery from Normandy (English Channel) were induced to spawn, and fertilized eggs were exposed to copper or cadmium for 24 h. Metal accumulation (from 0.125 to 5 microg Cu L(-1) and from 25 to 200 microg Cd L(-1)) and MT concentrations were measured in larvae. Compared to controls, larvae accumulated copper and cadmium with an increase in MT concentrations particularly with cadmium (i.e. 130.96 ng Cu (mg protein)(-1) and 12.69 microg MT (mg protein)(-1) at 1 microg Cu L(-1) versus 23.19 ng Cu (mg protein)(-1) and 8.92 microg MT (mg protein)(-1) in control larvae; 334.3 ng Cd (mg protein)(-1) and 11.70 microg MT (mg protein)(-1) at 200 microg Cd L(-1) versus 0.87 ng Cd (mg protein)(-1) and 4.60 microg MT (mg protein)(-1) in control larvae). Larvae were also obtained from oysters of a clean area (Arcachon Bay) and a polluted zone (Bidassoa estuary) and exposed to copper in the laboratory, their MT concentration was measured as well as biomarkers of oxidative stress. Biomarker responses and sensitivity to copper for the larvae from Arcachon oysters were higher than for those from Bidassoa.     

Lethal and sublethal toxicity of 4-nonylphenol to the common mussel (Mytilus edulis L.)

The toxicity of nonylphenol to the common mussel (Mytilus edulis L.) has been determined in both semistatic and continuous flow test systems. The LC50 values obtained were for 96 h, 30 mg litre(-1); 360 h, 0.5 mg litre(-1); and 850 h, 0.14 mg litre(-1). Sublethal effects, manifested as decreased byssus strength and change of scope for growth, were obtained at a concentration as low as 0.056 mg litre(-1). Fertilization and early developmental success were not affected at the highest concentration tested (0.2 mg litre(-1)).     

Effects of zinc on the structure and growth dynamics of a natural freshwater phytoplankton assemblage reared in the laboratory

The response of a natural phytoplankton assemblage to different concentrations of Zn(2+) was evaluated by means of a static laboratory bioassay. Aliquots of surface water, taken in autumn from a non-polluted point of the Reconquista River (Buenos Aires, Argentia), were incubated in mineral nutrient media containing 2.5, 10 or 25 mg litre(-1) of Zn(2+) (as zinc chloride). The comparative structure and dynamics of the communities were followed through periodic physico-chemical and biological analyses of samples taken during 24 days of incubation. Under the experimental conditions of the bioassays, the existence of several Zn(2+) tolerant algal species was shown: the most important of them were Chlorella vulgaris Beij. (Chlorophyceae, Chlorococcales), Nitzschia palea (Kütz.) Smith and Gomphonema parvulum (Kütz.) Kütz. (Bacillariophyceae). It was also demonstrated that the algal responses to Zn(2+) were selectively concentration dependent: at 2.5 and 10 mg litre(-1) a stimulatory effect was observed in the diatoms; at 25 mg litre(-1), diatom toxicity occurred. In contrast, Chlorophyceae growth was stimulated at the maximal Zn level. In general, the diversity, richness and equitability of the community were adversely affected by Zn in a concentration-dependent fashion.     

Bioaccumulation of cadmium by the freshwater isopod Asellus aquaticus (L.) from aqueous and dietary sources

Experiments were conducted to determine the kinetics and relative importance of aqueous and dietary uptake of cadmium by the freshwater isopod Asellus aquaticus (L.). Test animals were exposed during 30 days to aqueous Cd in a continuous flow system (exposure levels: 0.2 - 10 microg litre(-1)) and kept on a diet of previously contaminated Elodea sp. (range of Cd concentrations: 2-350 microg g(-1), dry weight). Preceding semi-static experiments on dosage-control of the dietary factor revealed a rapid uptake of Cd by Elodea, with relatively high concentration factors (CF), which ranged from 4.8 to 5.5 (dry weight log (CF) after 16 days). For Asellus uptake from water appeared to be the predominant route. Highly significant bioconcentration of cadmium from water was observed in the animals, even at exposure levels below 1.0 microg litre(-1). In the various treatments, direct uptake from water accounted for 50-98% of the body burdens after 30 days exposure. The experimental results were described with a first order one-compartment bioaccumulation model. Model parameter estimates (mean +/- standard error) were obtained for rate constant of uptake (560 +/- 110 day(-1)), rate constant of elimination (0.032 +/- 0.017 day(-1)) and assimilation efficiency of Cd uptake from food (1.1 +/- 0.7%). The (dry weight) bioconcentration factor (BCF) and bioaccumulation factor (BAF) for extrapolated steady state conditions were estimated at 18 000 (BCF) and 0.08 (BAF). Experiments conducted at two different pH levels (5.9 versus 7.6) revealed no significant effects of pH on the uptake of aqueous Cd by the isopods. The results are discussed in relation to their potential significance to the field situation.     

Bioaccumulation and critical body residue of PAHs in the amphipod,Diporeia spp: additional evidence to support toxicity additivity for PAH mixtures

Polycyclic aromatic hydrocarbons (PAHs) are considered to act additively when exposed as congener mixtures. Additive internal concentrations at the site of toxic action is the basis for recent efforts to establish a sum PAH guideline for sediment-associated PAH toxicity. This study determined the toxicity of several PAH congeners on a body residue basis in Diporeia spp. These values were compared to the previously established LR(50) value for a PAH mixture based on the molar sum of PAH congeners and demonstrated similar LR(50) values for individual PAH. These results support the contention that the PAH act at the same molar concentration whether present as individual compounds or in mixture. Aqueous exposures were conducted for 28 d, and the water was exchanged daily to maintain the exposure concentration. The concentration in the exposures declined by an average of 22% between water exchanges across all compounds, and ranged from 11% to 32%. The toxicokinetics were determined using both time-weighted-average (TWA) and time-variable water concentrations and were not statistically different between the two source functions. Toxicity was determined for both mortality and immobility (failure to swim on prodding) and on both a TWA water concentration and a body residue basis. The LC(50) values ranged from 1757 microg l(-1) for naphthalene after 10 d exposure to 79.1 microg l(-1) for pyrene after 28 d exposure, and the EC(50) ranged from 1587 microg l(-1) for naphthalene after 10 d exposure to 38.2 microg l(-1) for pyrene after 28 d exposure. The LR(50) values for all congeners at all lengths of exposure were essentially constant and averaged 7.5+/-2.6 micromol g(-1), while the ER(50) for immobility averaged 2.6+/-0.6 micromol g(-1). The bioconcentration factor declined with increasing exposure concentration and was driven primarily by a lower uptake rate with increasing dose, while the elimination remained essentially constant for each compound.     

Uptake of polycyclic aromatic hydrocarbons by Trifolium pretense L. from water in the presence of a nonionic surfactant

A greenhouse study examined plant uptake of phenanthrene and pyrene, as representatives of polycyclic aromatic hydrocarbons (PAHs), from an aqueous solution containing a nonionic surfactant Tween 80. The uptake was conducted with 1.0 mg l(-1) phenanthrene and 0.12 mg l(-1) pyrene under a wide range of Tween 80 concentrations (0-105.6 mg l(-1)). Tween 80 at the test concentrations did not show any apparent phytotoxity toward the growth of red clover (Trifolium pretense L.). At concentrations generally lower than 13.2 mg l(-1), Tween 80 enhanced the plant uptake based on the concentrations and PCFs (plant concentration factors) of these two PAHs. When present at higher concentrations, Tween 80 inhibited the uptake of both PAH compounds by the tested plant. The maximal plant uptake was observed at 6.6 mg l(-1) Tween 80, in which PAH concentrations and PCFs were 18-115% higher than those in Tween 80-free controls. The total mass removal (off-take) of phenanthrene and pyrene by root or shoot increased initially and decreased thereafter with the increase in Tween 80 concentrations. Although shoot biomass was evidently larger than root, the off-take was much higher in root than shoot because of the larger root concentrations of these chemicals. Results from this study show promises for the potential efficacy of enhanced phytoremediation in PAH contaminated sites using surfactant amendment.     

The fate of herbicide acetochlor and its toxicity to Eisenia fetida under laboratory conditions

To assess the toxic effects of the herbicide acetochlor on earthworms, we exposed Eisenia fetida (Savigny) to artificial soils (OECD soil) supplemented with different concentrations (5, 10, 20, 40 and 80 mg kg-1 soil) of acetochlor. The residues of acetochlor in soil and the effect of the herbicide on growth, reproduction, glutathione-S-transferases (GST) activity and cellulase activity of earthworms were determined. The degradation half-life of acetochlor in soil of acetochlor was between 9.3 and 15.6 days under laboratory condition; the degradation rate with low concentrations was faster than it was with higher concentrations. At 5 and 10 mg kg-1, acetochlor had not significant effect on growth of E. fetida except after 15 and 30 days of exposure. When concentration>20 mg kg-1, growth rates and numbers of juveniles per cocoon decreased significantly compared to the control in all treatments. However, cellulase activity decreased significantly in all treatments (5-80 mg kg-1). This study showed that acetochlor had no long-term effect on the growth and reproduction of E. fetida at field dose (5-10 mg kg-1). At higher concentrations of acetochlor (20-80 mg kg-1), acetochlor revealed sublethal toxicity to E. fetida. Growth, numbers of juveniles per cocoon and cellulase activity can be regarded as sensitive parameters to evaluate the toxicity of acetochlor on earthworms.