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PubMed1995

Microbial bioassays to assess the toxicity of solid-associated contaminants.

Due to the effects that sediment or soil matrices have on the bioavailability of compounds, it has been difficult to screen toxicity of solid-associated contaminants. The majority of microbial assays for testing toxicity of soils and sediments have been performed on water or solvent extracts. These procedures lead to a fractionation of the toxicity, which may underestimate or overestimate exposure routes and consequently potential adverse environmental effects. Recently, a solid-phase Microtox assay which eliminates the need for soil extracts and utilizes whole sediments or soils has been developed. This report describes a toxicity testing procedure using the inhibition of dehydrogenase enzyme activity of Bacillus cereus as test parameter. Studies with soil samples and a synthetic sediment spiked with organic contaminants and copper indicate the higher sensitivity of both solid-phase bioassays compared to water extract testing. A comparison of the results demonstrates that the B. cereus contact test is more sensitive for copper than the Photobacterium phosphoreum solid-phase test.

Bacillus cereus↗

PubMed1995

Effects of pentachlorophenol and biotic interactions on soil fauna and decomposition in humus soil.

In a laboratory experiment, effects of chemical stress (pentachlorophenol, PCP, at concentrations of 0, 50, and 500 mg/kg) and biotic interactions (nematodes in the presence or absence of collembolas and enchytraeids) on the community structure of soil animals and decomposition processes were studied. PCP was strongly adsorbed to humus that contained 65% organic matter. Numbers of fungal-feeding nematodes decreased significantly at the highest PCP concentration, while no effects were found in bacterial feeders. There were differences in the numbers of nematodes between different animal combinations, but at the highest PCP concentration, collembolas and enchytraeids had no effect on them. Numbers of collembola Willemia anophtalma were lowered at the highest PCP concentration, although PCP was not acutely toxic at this concentration. The highest PCP concentration was acutely toxic to enchytraeids, and for an unknown reason all of them died in the main experiment. Both ATP content of the soil and soil respiration were reduced at the highest PCP concentration, while no differences were found between animal treatments. Amounts of NH4-N and PO4-P in the soil increased with increasing PCP concentration. It was concluded that in the presence of simple animal communities, harmful chemicals like PCP regulate the community structure of soil animals as well as decomposition and nutrient mobilization.

Acholeplasma laidlawii↗

PubMed1995

Use of the bioluminescent bacterium Vibrio harveyi to detect biohazardous chemicals in soil and water extractions with and without acid.

An investigation was undertaken using the bioluminescence-reduction bioassay of Vibrio harveyi to study the toxicity of 31 chemicals in a soil and water extraction that was treated with and without hydrochloric acid. Soil had the chemical added and was washed with 0.2 N HC1 and afterward this acid-treated soil containing the chemical was evaluated. Each chemical was tested independently. Endpoints determined were either an estimated effective concentration at 50 or 20%, which was based on bacterial-luminescence remaining after treatment. This investigation suggests that metals are more effectively bound in treatments without acid than those with acid, while no difference in toxicity was observed for organics. In comparison to a previous study of toxicity using these chemicals in water, soil was effective in reducing toxicity as determined by this assay. However, each chemical appears to have its own unique toxicity characteristic when evaluated under different conditions.

Biodegradation, Environmental↗

PubMed1996

Effects of terbuthylazine on soil fauna and decomposition processes.

Acute lethal and sublethal effects of terbuthylazine and the commercial herbicide preparation Gardoprim [terbuthylazine is the active ingredient (a.i.)] on soil organisms (microbes, oppioid mites, two gamasid mite species, enchytraeids, and nematodes) were studied. In the humus soil terbuthylazine had no toxic effects on soil animals tested. However, the herbicide preparation had acute toxic effects on enchytraeids [no-observed-effect level (NOEL) 1.0 g a.i. /m2] and both gamasid mites (NOEL 2.4 and 5.0 g a.i./m2). According to filter paper test, the LC50 value for oppioid mites was 14.5 g a. i./m2. In the humus soil the commercial preparation caused no dose-related mortality in Oppioidea. The preparation was more toxic to gamasid mites when the herbicide was applied on the soil surface compared to the treatment in which the chemical was mixed into the humus. Application method of the chemical did not affect the mortality of enchytraeids. In the multispecies experiment, the number of nematodes was higher in the highest concentration of the commercial preparation (50 g a.i./m2) compared to the lowest concentration (1 g a.i./m2) and the clean soil. The amount of NH+4-N in the humus tended to increase with increasing herbicide concentration. The herbicide did not affect soil respiration, microbial biomass, or water content of the humus. These results indicated that herbicides can have direct effects on soil fauna. Due to species-specific foraging strategies or different exposure routes and rates to animals, effects of herbicides on soil animals varied considerably. Single-species toxicity tests performed in humus soil were more sensitive to the effects of herbicide than ecologically relatively short-term multispecies test.

Ammonia↗

PubMed1997

Toxicity of increased amounts of chemicals and the dose-response curves for heterogeneous microbial populations in soil.

The paper deals with the interpretation and classification of dose-response curves in order to understand the way in which the heterogeneous soil microbial population behaves under chemical stress. The evaluation is based on a set of about 500 toxicity tests, in which geometrically increasing doses of toxicants were applied to soil samples. The responses of the microflora were measured by various methods, e.g., Fe(III) reduction, substrate induced respiration, arginine ammonification, and several enzyme activities. The data reveal that microbial populations in soil react more complexly than homogeneous groups of test subjects which are common in classical toxicology. The diverse types of dose-response curves are attributed to a varying sensitivity of different parts of the soil microflora and influences of the habitat soil. A proposal for the interpretation and classification of microbial dose-response curves is presented. Four basic types of dose-dependent effects and several combined sequences of them can describe the reaction patterns found up to now. Since experiments with heterogeneous populations are lacking in classical toxicology, the results can be used as a key for further research regarding the toxicity of chemicals against plant, animal, and human populations.

Biomass↗

PubMed1997

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.

Bacteria↗

PubMed1998

Microbial toxicity in soil medium.

A laboratory procedure using the respirometer was developed to measure microbial toxicity in soils of organic chemicals. The procedure was tested with Polytox, a commercial microbial test culture, on 35 organic chemicals. The test protocol was reproducible with a mean standard deviation of 0.08 mg chemical/g of soil for eight chemicals. The assays were also carried out at different moisture-holding capacities of soil. Correlation between toxicity tests done in aqueous medium and soil for Polytox test culture was statistically significant and yielded an r2 of 0.816. Details of the laboratory procedure and test results are presented together with comparisons of toxicity of chemicals in the soil medium with that in aqueous medium for the same test organism. A few practical applications are discussed.

Bacteria, Aerobic↗

PubMedDate not supplied

Selection of a pesticide with low environmental impact.

The conditions were analyzed for evaluation of a mean soil biodegradation of a pesticide within a certain region. Different soils from two Czech and two German regions were used for a highly sensitive analysis based on a laboratory incubation of each isolated active soil strain with a radiolabeled pesticide. It was proved for all analyzed soils that the biodegradation activity of the total biomass was caused by only a small part of the present microbial strains. Not only bacteria, but also fungi and yeast have to be taken into consideration in a pesticide biodegradation. The biodegradation products were quantified by radio high-performance liquid chromatography.

Animals↗

PubMedDate not supplied

Development of a field bioassay for the side effects of pesticides on decomposition.

A method has been developed for assessing the side effects of fungicides on decomposition using litterbags. Twenty dried leaf disks of Chinese cabbage, Brassica oleracea, were placed in litterbags (20 x 20 cm) made of nylon fabric (25 microns mesh). The litterbags were laid in a treated plot and 5, 10, 20, and > 200 m from the treated plot and covered with 1 cm of standard soil. After 1 week, the dry weight of the leaf disks was determined. In an iterative procedure the method was optimized and significant differences of 5% in decomposition rate between litterbags were found using the final method presented here. In and around agriculturally managed plots, negative effects on decomposition of two fungicides could be traced. Effects on decomposition were found after application of captan (in fruit, 1.5 kg a.i./ha) and maneb (in potatoes, 3 kg a.i./ha) up to 10 m from the treated plot, at moderate wind speeds (3-5 m/s). In one case the concentration of captan in the soil covering the litterbags was measured. A negative correlation was established between captan concentration and decomposition. These experiments were repeated in an experimental plot under more controlled conditions with respect to the amount and time of application. The results of the field experiments could not be reproduced on the experimental plot. Additional experiments with soil fungi in agar again demonstrated a significant effect of exposure to captan, however. Given the results, the method using litterbags requires further development before a standard field trial can be designed. Given the knowledge gained with respect to the key factors involved, a bioassay using soil fungi seems to have high potential, however.

Biodegradation, Environmental↗

PubMedDate not supplied

Assessment of the ecotoxic potential of soil contaminants by using a soil-algae test.

To assess the ecotoxic potential of soil contaminants, a test with the soil alga Chlorococcum infusionum has been developed, enabling investigations of soil pollutions with soluble and fairly soluble chemicals. Three soil types artificially contaminated with Sb compounds and five soils from a historical mining area, which were highly polluted with Sb, As, Hg, and Cu, were used as test soils. For antimony, EC50 values from 125 mg/kg up to > 1000 mg/kg, depending on soil type, were determined. Two of five soils from the mining area caused toxic effects. Additionally, aqueous extracts of all soils were exposed in established tests (daphnid, alga, bacterium). In contrast with the soil-algae test, no toxic effects were found. Aquatic tests with SbO/K tartrate were performed to point out the toxicity of antimony. The following EC50 values in milligrams of Sb per liter were determined: Scenedesmus subspicatus, 59 mg/liter; Chlorococcum infusionum, 43 mg/liter; Daphnia magna, 8 mg/liter; and Vibrio fisheri, 7 mg/liter.

Animals↗

PubMed1999

Effects of organic pollutants on soil microbial activity: the influence of sorption, solubility, and speciation.

The Fe(III) reduction test was used to measure the toxicity of 12 organic chemicals [dichlorophenoxyacetic acid (2,4-D), trichlorophenoxyacetic acid (2,4,5-T), atrazine, picloram, 4-chlorobenzeneamine, pentachlorophenol (PCP), hexachlorobenzene (HCB), 1,1-bis-4-chlorophenyl-2,2,2-trichloroethane (DDT), trichloroethene, benzene, phenol, linear alkylbenzenesulfonate (LAS)]. The different inherent toxicity of the pollutants is strongly modified by interactions with the soils. The total amounts that cause 10, 50, and 90% inhibitions (effective doses, ED10, ED50, ED90) can be statistically related to soil parameters that control the sorption and solubility of the chemicals. Sorption experiments with 2,4-D, 2,4,5-T, PCP, and LAS confirm that the degree of sorption and the concentration in the soil solution are important for potential toxic effects. However, toxic solution concentrations of a chemical (effective concentrations, EC10, EC50, EC90) also vary considerably. For some chemicals the influence of soil pH on their speciation in the soil solution is mainly responsible for this, e.g., the transformation from anionic to nonionic species with decreasing pH. The nonionic species of 2,4-D, 2,4,5-T, and PCP formed under acidic conditions are more toxic than the anionic species. Thus, depending on the chemical parameters of the soils that determine the degree of sorption and the speciation of toxicants in the liquid phase, soils either can "buffer" high loads of toxicants or can be very sensitive toward contamination.

Dose-Response Relationship, Drug↗

PubMed1999

Effects of heavy metals on methane production in tropical rice soils.

In a laboratory incubation study, the effect of select heavy metals on methane (CH(4)) production in three rice soils was investigated under flooded conditions. Heavy metals behaved differently in their effect on methanogenesis in different soils and methane-producing bacteria. Cd, Cu, and Pb inhibited CH(4) production in all the soils. Zn stimulated CH(4) production in the alluvial soil, but inhibited it in laterite and acid sulfate soils. Cr effectively inhibited CH(4) production in the alluvial soil, but stimulated it in laterite and acid sulfate soils. The stimulatory effect of Zn and the inhibitory effect of Cr on methanogenesis in alluvial soil were attributed to their stimulation or inhibition of methanogenic bacterial population.

Bacteria↗

PubMed1999

Influences of copper forms on the toxicity to microorganisms in soils.

Soil samples with wide ranges of pH (4.9 to 8.1), organic carbon (0.1 to 77%), and total Cu contents from 32 to 11700 mg kg(-1), collected near a copper mine, were used to investigate the relationships between microbial features and Cu speciation in order to clarify the form(s) of Cu adversely affecting microorganisms. The effects of Cu on soil microorganisms were evaluated by two indicators: the ratio of microbial biomass carbon to soil organic carbon (Cmic/Org-C) and Cu tolerance level of bacterial community (IC50). The sequential extraction scheme of McLaren and Crawford (1973) was used to quantify the different Cu forms (soluble and exchangeable, specifically adsorbed, and organically bound). These influences were investigated using simple correlation analysis, multiple regression analysis, and principal component analysis. The IC50 was positively correlated with the log concentration of soluble and exchangeable Cu (Ex-Cu) (r = 0.757, P<0.01). The IC50 value was also influenced by the amount of specifically adsorbed Cu. The Cmic/Org-C ratio was not significantly correlated with any Cu forms. Thus, other soil properties had more influence on the size of microbial biomass carbon in the soils used. The amount of Ex-Cu exerting high toxicity was affected by pH and the amount of total Cu.

Carbon↗

PubMed1999

Usefulness of the sensitivity-resistance index to estimate the toxicity of copper on bacteria in copper-contaminated soils.

Examination was made of the fluctuations of numbers of the total bacteria and copper (Cu)-resistant bacteria with soluble/exchangeable Cu (Ex-Cu) fraction in three types of soils spiked with Cu at four concentrations. Drastic increase in Cu-resistant bacteria was observed in three soils spiked with 20 mmol Cu kg(-1) after 2 weeks of incubation, indicating the strong selection of individuals originally resistant to Cu. Adaptation and proliferation of bacteria were also observed in the soil environment under the long-term exposure to extremely high concentration of Cu (800 mg kg(-1) soil of Ex-Cu), deriving from the development of Cu resistance. These bacterial fluctuations and the toxic effects of Cu depended on soil types, due to the chemical forms in which Cu occurs. It was also found that the ratio of Cu-resistant bacterial number to total bacteria was significantly correlated with the amount of Ex-Cu in the soils. This sensitivity-resistance index seems to be useful for evaluating the toxic effects of Cu on the soil bacterial community. Whereas the toxicity of Cu depended on the soil properties, they also changed with time. This phenomenon can be explained by the decrease in the most labile Cu phase, Ex-Cu, with time in the soils.

Adaptation, Physiological↗

PubMed2000

A stepwise procedure for assessment of the microbial respiratory activity of soil samples contaminated with organic compounds.

Soil respiration measurements are used frequently for the characterization of soil samples. Identical methods are used for the ecotoxicological characterization of contaminated soil samples as well as for quantification of the active microbial biomass in agriculturally used soils. In this study four soil samples contaminated with large amounts of volatile organic compounds, polyaromatic hydrocarbons, or nitroaromatic compounds are characterized after stepwise addition of carbon, nitrogen, and phosphorus. The respiration kinetics are assessed over a period of 5 days. By means of qualitative evaluation of the results, it is demonstrated that this stepwise addition allows one to distinguish between growth-promoting effects of biodegradable organic compounds on the one hand and the toxic influence of these compounds on the other hand. Finally it is stated that a comprehensive ecotoxicological characterization cannot be performed routinely using only one or several parameters of respiration curves. There is need for further research and validation if soil respiration measurements are to be performed quantitatively in the future.

Environmental Monitoring↗

PubMed2000

An in situ respirometric technique to measure pollution-induced microbial community tolerance in soils contaminated with 2,4, 6-trinitrotoluene.

Long-term exposure to 2,4,6-trinitrotoluene (TNT) can induce changes in the structure and activities of soil microbial communities. Such changes may be associated with an elevated microbial tolerance. An in situ respirometry technique based on the analysis of the substrate-induced respiration response to freshly added TNT was used to examine soil microbial tolerance to TNT at the community level. The specific growth rate derived by fitting an exponential equation to respiration data was taken as the measurement endpoint. Microbial tolerance was evaluated using a tolerance index defined as the ratio of the specific growth rate at a spiking dose of 2000 microg TNT/g soil to that of the control with no spiked TNT. Three soils with long-term exposure histories (TNT level in soil: 1.5, 32, and 620 microg TNT/g, respectively) exhibited significantly higher microbial community tolerance to TNT than two uncontaminated control soils. A soil containing 29,000 microg TNT/g exhibited the highest tolerance. Findings from this study support the hypothesis that pollution-induced community tolerance can be used as a means of identifying those compounds that have exerted selective pressure on the community.

Dose-Response Relationship, Drug↗

PubMed2000

Influence of heavy metals on methane oxidation in tropical rice soils.

In a laboratory incubation study, the effect of select heavy metals on methane (CH4) oxidation in two rice soils was investigated under two moisture regimes. Heavy metals differed in their effect on CH4 oxidation in both soils under the two water regimes. Cr significantly inhibited CH4 oxidation in the alluvial soil at 60% moisture holding capacity, while Cu stimulated the process. On the contrary, Zn inhibited CH4 oxidation in both alluvial and laterite soils only under flooded conditions. Application of rice straw alleviated the inhibitory effect of heavy metals on CH4 oxidation and CO2 production. Inhibition of CH4 oxidation in the alluvial soil was related to the methanotrophic bacterial population in Cr- and Zn-amended alluvial soil.

Metals, Heavy↗

PubMed2002

Microbial toxicity tests and chemical analysis as monitoring parameters at composting of creosote-contaminated soil.

Traditionally, chemical analyses are used in the assessment of contaminated soil and in monitoring the efficiency of soil remediation processes. We investigated if chemical analysis could be supported and even partly replaced by biological toxicity tests. In two case studies creosote-contaminated soil was composted outdoors in 5- and 100-m3 windrows. Degradation of polyaromatic hydrocarbons (PAHs) was followed by chemical analysis and toxicity tests. Polyaromatic hydrocarbons were quantified and identified by HPLC. Because the soil was also contaminated by copper-, chromium-, and arsenic-containing fungicides, these elements were analyzed by atomic absorption spectrometry. The toxicity of soil samples was assessed by a soil-contact modification of the luminescent bacteria (Vibrio fischeri) test and in the other case also by enzyme synthesis inhibition (Toxi-ChromoPad test, Escherichia coli). The toxicity of soil water extracts was measured by the standard luminescent bacteria (V. fischeri) test and bacterial (Pseudomonas putida) growth inhibition test. After the first 4 months of the composting period the total amount of PAHs was reduced in all windrows, and in particular, the loss of two- and some three-ring compounds was high, almost 90%. Toxicity decreased concurrently with the decrease in PAH concentration during composting, but after 4 months, one of the piles inoculated with mycobacteria and containing more three- and four-ring compounds was found to be more toxic than at the beginning. After the next summer, total PAH content was further reduced but some four-ring or heavier compounds were demonstrated to be poorly degraded. The toxicity was also reduced to the same level as in the control pile. The total PAH content and the toxicity were both reduced significantly during 5 months of composting.

Biodegradation, Environmental↗