The use of bioassays for evaluating the toxicity of sewage sludge and sewage sludge-amended soil

Background and Aims  

In soils, the most commonly mentioned hazardous substances are metals. One of the sources of its accumulation is the application of sewage sludge. However, little information is available regarding the estimation of the toxicity of sewage sludge or soil treated with sewage sludge, even by means of a battery of bioassays. In this study an evaluation of a battery of bioassays was carried out for toxicity assessment of sewage sludge and sewage sludge-treated soil. The objectives of this study were a) to compare the sensitivity of the different bioassays for the toxicity determination of sewage sludge contaminated with metals and soil treated with this sewage sludge, b) to elaborate a procedure for the attribution of sewage sludge samples to hazard classes based on the ecotoxicological data, and c) to evaluate the suitability of elutriate bioassays and microbial toxicity tests for the assessment of sewage sludge-treated soil.     

Toxicity of arsenic in relation to soil properties: implications to regulatory purposes

Purpose

The present work evaluates the influence of different soil properties and constituents on As solubility in laboratory-contaminated soils, with the aim of assessing the toxicity of this element from the use of bioassays to evaluate the soil leachate toxicity and thereby propose soil guideline values for studies of environmental risk assessment in soil contamination.

Materials and methods

Seven soils with contrasting properties were artificially contaminated in laboratory with increasing concentrations of As. Samples were incubated for 4 weeks, and afterwards, soil solution (1:1) was obtained after shaking for 24 h. The soil leachate toxicity was assessed with two commonly used bioassays (seed germination test with Lactuca sativa and Microtox ® test with Vibrio fischeri).

Results and discussion

The relationship between soluble As and soil properties indicated that iron oxides and organic matter content were the variables most closely related to the reduction of the As solubility, while pH and CaCO₃ increased As solubility in the soil solutions. Toxicity bioassays showed significant differences between soils depending on their properties, with a reduction of the toxicity in the iron-rich soil (no observed effect concentration (NOEC)?=?150 mg kg^?1) and a significant increase in the highly carbonate samples (NOEC between 15 and 25 mg kg^?1).

Conclusions

Soil guideline values for regulatory purposes usually set a single value for large areas (regions or countries) which can produce over- or underestimation of efforts in soil remediation actions. These values should consider different levels according to the main soil properties controlling arsenic mobility and the soil leachate toxicity.     

Protozoan bioassays of soil amended with sewage sludge and heavy metals,using the common soil ciliate Colpoda steinii

The common soil protozoan Colpoda steinii was used to study the toxicity of sulphate solutions of Ni, Cd, Cu, and Zn. The growth of C. steinii was reduced by 50% in the presence of 0.10, 0.22, 0.25, and 0.85 mg litre^-1 of Ni, Cd, Cu and Zn, respectively, during 24 h of incubation at 25°C, as calculated from a regression analysis of probit-transformed data. The same growth assay was used to assess the toxicity of soil solution extracted by centrifugation from soil samples of field plots of a grass/clover ley on a sandy loam treated with sewage sludge spiked with additional Cd, Cu, Cr, Ni, Pb, or Zn at concentrations either equivalent to or twice the limits for heavy metals recommended in recent EC guidelines (Commission of European Communities directive 86/278/EEC). The toxicity of these soil solutions varied with the season of the year. None of the soil solutions extracted in winter (February 1991) inhibited the growth of C. steinii. In summer (July 1991), the growth was reduced in solutions extracted from plots that were amended with sludge plus additional Zn or Ni at twice the maxima recommended by the EC. The changes in toxicity to C. steinii of the soil solutions between February and July were positively correlated with increases in heavy metal concentrations of Zn and Ni between winter and summer. These preliminary results suggest that regular protozoan bioassays may be used to monitor the biological availability of heavy metals in soils, especially when combined with other microbial assays and with chemical analyses of soil solutions.     

Impact of controlled redox conditions on nickel in a serpentine soil

Purpose  

Serpentine soils exist in many regions around the world; they are naturally enriched with nickel (Ni). An adequate understanding of soil processes determining Ni solubility is a special need particularly since less research has been addressed to Ni behavior under dynamic and controlled redox conditions. Our aim was (1) to characterize the properties of a serpentine soil and (2) to determine the impact of predefined redox windows on the mobility and dynamics of Ni in a serpentine soil.     

Assessing chromate availability in tropical ultramafic soils using isotopic exchange kinetics

Background, aim, and scope  

The presence of labile chromate in the soils is an environmental problem because of its high toxicity. The isotopic exchange kinetics (IEK) methods have been shown to be a useful tool to measure the phytoavailability of major (P, K) and trace elements (Cd, Zn, Ni, Pb) in soils. This study focused on the potential of applying IEK for chromate to characterize its availability in two tropical ultramafic Ferralsols.     

Heavy metal content and toxicity of mine and quarry soils

Purpose

Soils formed in metallic mines and serpentinite quarries, among other unfavourable features, have high levels of heavy metals. They can release into the environment causing surface and subsurface water contamination, uptake by plants, their accumulation in the food chain and adverse effects on living organisms. In this work, we studied the magnitude of the soils’ toxic effects not only on spontaneous plants but also on two species with phytoremediation potential.

Materials and methods

Several soils from two different exploitations were selected: a lead and zinc mine and a serpentinite quarry. Soils were characterized, and the pseudo-total and extractable contents of Co, Cr and Ni in soils from a serpentinite quarry were determined. The Cd, Pb and Zn pseudo-total and extractable contents were determined in soils developed in the Pb/Zn abandoned mine. Using a biotest, the chronic toxicity of the soil samples on higher plants was determined. Festuca ovina L., Cytisus scoparius (L.) Link., Sinapis alba L. and Brassica juncea L. were selected, the first two because they are spontaneous plants in the study areas and the last two because they have heavy metal phytoremediation potential.

Results and discussion

Pseudo-total contents of Co, Cr and Ni in the serpentinite quarry soils and of Zn, Pb and Cd in the Zn/Pb mine soils exceed generic reference levels. CaCl₂ is the reactant that extracts the highest proportion of Co, Cr and Ni in the quarry soils and EDTA the largest proportion of Pb Zn and Cd content in the mine soils. The germination index values based on seed germination and root elongation bioassays revealed increasing plant sensitivity to the mine soils in the following order: B. juncea?<?S. alba?<?F. ovina?<?C. scoparius. The wide range of GI values indicates that the response of test plants to soil heavy metals depended on their concentrations and soil characteristics, especially pH and organic matter content.

Conclusions

The pollution index indicates severe Cd, Pb and Zn contamination in the mine soils, as well as high Cr and Ni and moderate Co contamination in the serpentinite quarry soils. The performed biotests were suitable for identifying toxic soils and showed that the studied soils are toxic to the spontaneous plants, more to C. scoparius than to F. ovina. They also indicate that the mine soils are more toxic than the quarry soils for both species.

     

Effectiveness of amendments to restore metal-arsenic-polluted soil functions using Lactuca sativa L. bioassays

Purpose

Because the success of the stabilisation of contaminants from amendments depends on the pollutants involved and the amendments used, the goals of this study were to assess whether selected amendments are able to restore highly polluted soils and to advance the knowledge of both the most suitable amendments to restore polluted soils and the most appropriate bioassays to estimate soil toxicity.

Materials and methods

An acidic and polluted soil from mining waste was amended with marble sludge, compost and iron in nine different combinations. The soils were placed in plastic pots and bioassays, including the different stages in the development of lettuce (Lactuca sativa L.), were carried out. Pore water was analysed at the different stages of the development of lettuce. At the end of the experiment, pollutant concentrations in lettuce leaf were analysed and the sequential extraction of trace elements was performed.

Results and discussion

The effectiveness of the amendments in reducing the toxicity of contaminated soils varied depending on the bioassay used. Marble sludge was the most effective in increasing pH and in reducing pollutant concentrations in pore water, clearly encouraging germination, root elongation and emergence. Throughout the emergence phase, marble sludge decreased in its effectiveness, probably because the pollutants precipitated as hydroxides and carbonates were taken up by the lettuce. In contrast, the compost began to improve the elongation of the seedling and the growth of lettuce. Although the amendments were effective in reducing the negative impact of pollutants in soils, none of them was able to successfully restore the functions of highly polluted soil.

Conclusions

The development of the plant until the end of the establishment phase is the best index to estimate soil phytotoxicity, although the effect on the health of potential consumers can only be evaluated from the toxic element concentrations in the plant. The uptake of pollutants stabilised by the amendments would explain why the reduction of easily available pollutant concentrations does not necessarily imply the restoration of the normal functioning of the ecosystem.     

Lability and sorption of heavy metals as related to chemical,physical, and mineralogical characteristics of highly weathered soils

Purpose  

Heavy metal lability, probably, is the most important isolated factor to cause toxicity in plants and organisms in soils. Sorption of heavy metals, in turn, affects directly the amount of their labile forms in soils. Therefore, to assess sorption and quantify labile forms of Cd, Cu, Ni, Pb, and Zn, adsorption and incubation studies were carried out.     

Toxicity of phenmedipham and carbendazim to Enchytraeus crypticus and Eisenia andrei (Oligochaeta) in Mediterranean soils

Purpose

The main objective of the present study was to evaluate the toxicity of two reference chemicals, Carbendazim and Phenmedipham, for the compostworm Eisenia andrei (effects of Carbendazim) and the potworm Enchytraeus crypticus (effects of Phenmedipham) in 12 Mediterranean soils with contrasting soil properties. The observed toxicity was also compared to that obtained for OECD standard soil, used as a control.

Materials and methods

The soils were selected to be representative for the Mediterranean region and to cover a broad range of soil properties. The evaluated endpoints were avoidance behavior and reproduction. Soils were also assembled in two groups according to their pedological properties.

Results and discussion

Toxicity benchmarks (AC50s) obtained for E. andrei avoidance behavior in carbendazim-contaminated soils were generally higher for sandy soils with low pH. The toxic effects on the reproduction of the compostworms were similar in the six tested soils, indicating a low influence of soil properties. The avoidance response of E. crypticus towards Phenmedipham was generally highly variable in all tested soils. Even though, a higher toxicity was observed for more acidic soils. The EC50s for reproduction of the latter species varied by a factor of 9 and Phenmedipham toxicity also tended to be increasing in soils with lower pH, except for the soils with extreme organic matter content (0.6 and 5.8%).

Conclusions

A soil effect on chemical toxicity was clearly confirmed, highlighting the influence that test soils can have in site-specific ecological risk assessment. Despite some relationships between soil properties and toxicity were outlined, a clear and statistically significant prediction of chemical toxicity could not be established. The range of soil properties was probably narrow to give clearer and more consistent insights on their influence. For the four groups of tests, the toxicity observed for OECD soil was either similar, lower, or generally higher if compared with Mediterranean soils. Moreover, it did represent neither the organic matter content found in Mediterranean soils nor their textural classes.     

Biological and chemical characterization of harbour sediments from the Stockholm area

Purpose  

The main objective of the current study was to assess the impact of pleasure boat activities on harbour sediment quality in the Stockholm area. Sediment contamination is a growing ecological issue, and there is consequently a need to use sediment bioassays in combination with chemical analysis to determine the impact on the ecosystem. To generate sediment toxicity data relevant for the Baltic Sea, a secondary objective was to further develop and evaluate two well-established bioassays for saltwater, with the macroalga Ceramium tenuicorne and the crustacean Nitocra spinipes, to be useful also for toxicity testing of whole sediment. A major concern has been to minimize any manipulation of the sediments. A third objective was to assess whether a simple leaching procedure could be used to simulate sediment toxicity by comparing results from whole sediment and leachate tests.     

Biochar-application rate and method affect nutrient availability and retention in a coarse-textured,temperate agricultural Cambisol in a microcosm experiment

Background

Agricultural soils often require organic amendments, which improve crop yield and ecosystem services. Biochar has been proven to increase nutrient availability and retention in fine-textured, tropical soils.

Aims

Here we determine how coarse-textured, temperate soils react to different biochar-application rates in different tillage systems.

Methods

We conducted a 6-month laboratory incubation experiment in microcosms filled with a coarse-textured, temperate agricultural soil to determine the effects of biochar-application rate (none, low, or high, i.e., 0, 20, or 40 t dw ha⁻¹, respectively) and application method (mixed into the soil or applied to the soil surface) on microbial activity and biomass, and nutrient availability and leaching.

Results

Microbial activity and biomass and contents of carbon, nitrogen, and phosphorus in leachates were higher in biochar-addition treatments (by 134%, 37%, 372%, 28%, and 801%, respectively) than in the no-addition treatment. The effect was stronger with the low than with the high biochar-application rate. Biochar applied by both methods acted as a slow-release fertilizer, but this effect was stronger when biochar was mixed into the soil. Although available nutrient contents in the soil remained high, nutrient leaching decreased with incubation time. This effect was especially evident when biochar was mixed into the soil.

Conclusions

Biochar is an effective organic amendment in coarse-textured soils providing available nutrients. On the other hand, nutrient-retention mechanisms develop slowly after biochar application and may be greater when biochar is mixed into the soil than applied on the soil surface.     

Bioaccumulation and toxicity of lead,influenced by edaphic factors: using earthworms to study the effect of Pb on ecological health

Purpose

Lead (Pb) is a highly studied contaminant with no known biological function that causes harmful adverse effects on ecological and human health. We tried to evaluate how protective the current soil regulatory levels are for Pb towards safeguarding the ecological health. In order to achieve this, our study evaluated the effect of soil texture and pH on the toxicity and availability of lead to earthworms in soils varying in soil properties.

Materials and methods

The earthworm Eisenia fetida was exposed to Pb in three soils with different physico-chemical characteristics. Pb solutions were homogenously mixed with soil to obtain concentrations ranging from 0 to 10,000 mg/kg Pb dry soil. Avoidance behaviour, weight loss and mortality were measured in this study to calculate the EC₅₀ and LC₅₀ values.

Results and discussion

Weight loss and mortality in earthworms due to Pb toxicity were in the following order: acidic > neutral > alkaline soil. The EC₅₀ values resulting in 50% decrease in worm weight over control for Pb in acidic, neutral and alkaline soils were 460, 3606 and 5753 mg/kg soil, respectively. Thus, the acidic soil recorded an EC₅₀ well below the soil guideline value for Pb. Whereas, the LC₅₀ values resulting in 50% mortality in worms over control were 1161, 4648 and 7851 mg/kg, respectively, for acidic, neutral and alkaline soils. The Pb concentrations in earthworms ranged from 0.2 to 740 mg/kg wet weight. Soils with low clay content and acidic to neutral pH values demonstrated an increased Pb toxicity in earthworms compared to the soils with alkaline pH.

Conclusions

The worm weight loss is a more sensitive parameter than the mortality. This study emphasizes that the soil regulatory levels for Pb are not protective of worms in acidic soils. Therefore, care should be taken when using the current regulatory limits to assess and predict the safety of a contaminated site with acidic soils towards the ecological health.

     

Speciation of heavy metals in garden soils: evidences from selective and sequential chemical leaching

Purpose  

Gardening (especially food growing) in urban areas is becoming popular, but urban soils are often very contaminated for historical reasons. There is lack of sufficient information as to the bioavailability of soil heavy metals to plants and human in urban environments. This study examines the relative leachability of Cr, Ni, As, Cd, Zn, and Pb for soils with varying characteristics. The speciation and mobility of these metals can be qualitatively inferred from the leaching experiments. The goal is to use the data to shed some light on their bioavailability to plant and human, as well as the basis for soil remediation.     

Cu and Ni Mobility and Bioavailability in Sequentially Conditioned Soils

The potential ecological hazard of metals in soils may be measured directly using a combination of chemical and biological techniques or estimated using appropriate ecological models. Terrestrial ecotoxicity testing has gained scientific credibility and growing regulatory interest; however, toxicity of metals has often been tested in freshly amended soils. Such an approach may lead to derivation of erroneous toxicity values (EC₅₀) and thresholds. In this study, the impact of metal amendments on soil ecotoxicity testing within a context of ion competition was investigated. Four coarse-textured soils were amended with copper (Cu) and nickel (Ni), incubated for 16 weeks and conditioned by a series of total pore water replacements. Rhizon^TM extracted pore water Cu, Ni, pH and dissolved organic carbon (DOC) concentrations were measured after each replacement. Changes in ecotoxicity of soil solutions were also monitored using a lux-based biosensor (Escherichia coli HB101 pUCD607) and linked to variations in soil solution metal and DOC concentrations, pH and selected characteristics of the experimental soils (exchangeable calcium (Ca) and magnesium (Mg)). Prior to conditioning of soils, strong proton competition produced relatively high EC₅₀ values (low toxicity) for both, Cu and Ni. The successive replacement of pore waters lead to a decline of labile pools of metals, DOC and alleviated the ecotoxicological protective effect of amendment impacted soil solution chemistry. Consequently, derived ecotoxicity values and toxicity thresholds were more reflective of genuine environmental conditions and the relationships observed more consistent with trends reported in historically contaminated soils.     

Applying a GLM-based approach to model the influence of soil properties on the toxicity of phenmedipham to Folsomia candida

Purpose

Soil properties are the main explanation to the different toxicities obtained in different soils due to their influence on chemical bioavailability and the test species performance itself. However, most prediction studies are centred on a few soil properties influencing bioavailability, while their direct effects on test species performance are usually neglected. In our study, we develop prediction models for the toxicity values obtained in a set of soils taking into account both the chemical concentration and their soil properties.

Materials and methods

The effects on the avoidance behaviour and on reproduction of the herbicide phenmedipham to the collembolan Folsomia candida is assessed in 12 natural soils and the Organisation for Economic Co-operation and Development (OECD) artificial soil. The toxicity outcomes in different soils are compared and explanatory models are constructed by generalised linear models (GLMs) using phenmedipham concentrations and soil properties.

Results and discussion

At identical phenmedipham concentrations, the effects on reproduction and the avoidance response observed in OECD soil were similar to those observed in natural soils, while effects on survival were clearly lower in this soil. The organic matter and silt content explained differences in the avoidance behaviour in different soils; for reproduction, there was a more complex pattern involving several soil properties.

Conclusions

Our results highlight the need for approaches taking into account all the soil properties as a whole, as a necessary step to improve the prediction of the toxicity of particular chemicals to any particular soil.     

Contrasting response of nitrification capacity in three agricultural soils to N addition during short-term incubation

Purpose

Human disturbance is a major culprit driving imbalances in the biological transformation of nitrogen from the nonreactive to the reactive pool and is therefore one of the greatest concerns for nitrogen (N) cycling. The objective of this study was to compare potential nitrification rates and the abundance of ammonia oxidizers responsible for nitrification, with the amendment of external N in different agricultural soils.

Materials and methods

Three typical Chinese agricultural soils, QiYang (QY) acid soil, ShenYang (SY) neutral soil, and FengQiu (FQ) alkaline soil, were amended with 0, 20, 150, and 300 μg NH₄ ⁺-N g^?1 soil and incubated for 40 days. The abundance of ammonia oxidizing bacteria (AOB) and archaea (AOA) at the end of incubation in the soil microcosms was determined using the real-time PCR.

Results and discussion

There was a significant decrease in ammonium concentration in the QY soil from the highest to the lowest N-loading treatments, while no significant difference in ammonium concentrations was detected among the different N-loading treatments for the SY and FQ soils. A significantly higher potential nitrification rate (PNR) was observed in the FQ soil while lowest PNR was found in the QY soil. Quantitative PCR analysis of AOB amoA genes demonstrated that AOB abundance was significantly higher in the high N-loading treatments than in the control for the QY soil only, while no significant difference among treatments in the SY and FQ soils. A significant positive correlation between PNR and AOB amoA abundance, however, was found for the SY and FQ soils, but not for the QY soil. Little difference in AOA amoA abundance between different N-loading treatments was observed for all the soils.

Conclusions

This study suggested that ammonia oxidation capacity in the FQ and SY soils was higher than those in the QY soil with the addition of ammonium fertilizer for a short-term. These findings indicated that understanding the differential responses of biological nitrification to varying input levels of ammonium fertilizer is important for maximizing N use efficiency and thereby improving agricultural fertilization management.     

Evidence of dissolved trivalent manganese in acidic forest soils

Background

Evidence of trivalent manganese (Mn³⁺) in the aqueous phase of soils is unknown so far although this strong oxidant has large environmental implications.

Aims

We aimed to modify a spectrophotometric protocol (porphyrin method) and to discriminate between Mn²⁺ and Mn³⁺ in the aqueous phase of forest soils based on kinetic modeling.

Methods

We investigated manganese speciation in 12 forest floor solutions and 41 soil solutions from an acidic forest site by adjusting pH and correcting for absorbance.

Results

The solutions showed broad ranges in pH (3.4−6.3), dissolved organic carbon (DOC, 1.78−77.1 mg C L⁻¹), and total Mn (Mn_T, 23.9−908 µg L⁻¹). For acidic solutions, a pH-buffer was added to increase the pH of the solutions to 7.5−8.0, and background absorption was corrected for colored solutions, that is, solutions high in DOC. This was done to accelerate the reaction kinetics and avoid overestimation of Mn_T concentrations. After the pH and color adjustments, the comparison of Mn_T concentrations between the porphyrin method and optical emission spectrometry showed good agreement. Trivalent Mn, which is stabilized by organic ligands, constitutes significant proportions in both forest floor solutions (10−87%) and soil solutions (0.5−74%).

Conclusions

The dissolved Mn³⁺ is present in acidic forest soils. Thus, we revise the paradigm that this species is not stable and encourage to apply the revised method to other soils.     

The use of a microbial contact toxicity test for evaluating cadmium bioavailability in soil

Background, Aims and Scope

Bioavailability of toxic compounds in soil can be defined as the fraction able to come into contact with biota and to cause toxic effects. The contact toxicity tests may detect the total toxic response of all bioavailable contaminants present in a sample. The objectives of this study were to evaluate the use of microbial contact toxicity tests for cadmium bioavailability assessment and to evaluate the relationship between sorption, soil characteristics and cadmium bioavailability.

Methods

A test soil bacterium,Bacillus cereus, was put in direct contact with the solid sample. Four unpolluted soils were selected to provide solid samples with a variety of physicochemical characteristics. The toxicity and sorption behaviour of cadmium spiked to the soil samples were determined.

Results, Discussion and Conclusions

A significant correlation between contact toxicity test results and partitioning of cadmium in the soil samples (r²= 0.79, p <0.05; n = 26) was found. The results confirm that the bioavailability of cadmium in soil depends on its sorption behaviour. Cadmium sorbed to the cation exchange sites associated with fulvic acids is non-bioavailable in the toxicity test employed in this study. It is concluded that the microbial contact toxicity test is a suitable tool for detecting cadmium bioavailablity in the soils used in this study.

Outlook

The application of microbial contact toxicity tests for bioavailability assessment can be very useful for the risk identification and remediation of soil-associated contaminants.     

Effects of ozonation on soil organic matter of contaminated soil containing residual oil

Purpose  

Ozonation has been shown to be a feasible method for removal of organic pollutants resistant to biodegradation in contaminated soils. However, little is known about the impact of ozonation on soil organic matter (SOM). This study was conducted to investigate the change in SOM characteristics and the consequent change in sequestration of contaminants in soil during ozonation.     

Evaluation of toxicity risk of polycyclic aromatic hydrocarbons (PAHs) in crops rhizosphere of contaminated field with sequential extraction

Purpose

The assessing bias of rhizosphere effect on polycyclic aromatic hydrocarbons (PAHs) degradation in soils would come out from formation of nonextractable PAHs and extractability difference of various solvents. The aim of this study was to evaluate the role of rhizosphere effect in long-term PAHs polluted soils by using sequential extraction approach.

Material and methods

The scheme of sequential extraction included methanol/water extractable PAHs, butanol extractable PAHs, DCM extractable PAHs, humic acid-bound PAHs, crude humin-bound PAHs, and organic-C enriched humin-bound PAHs. PAHs in plant tissues were extracted by dichloromethane after saponifying. The correlations between PAHs in plant tissues and sequentially extracted fractions were generated by partial least squares regression.

Results and discussion

The profiles of sequentially extracted PAHs varied with plant species. The discrepancy of toxicity equivalency concentrations between rhizosphere and bulk soils was much more significant than that of total PAHs concentrations. In partial least squares regression models, the concentration of PAHs in plant tissues was correlated with fractions strongly associated with soil.

Conclusions

The novelty of this study is the evaluation of concentration and toxicity equivalency concentration of PAHs in rhizosphere of crops sampled in a field polluted with PAHs for long term. This study has highlighted more significant role of rhizosphere in cleanup of cancerogenic toxicity of soil than amount of PAHs in polluted soils.