An increasing body of evidence suggests that microorganisms are far more sensitive to heavy metal stress than soil animals or plants growing on the same soils. Not surprisingly, most studies of heavy metal toxicity to soil microorganisms have concentrated on effects where loss of microbial function can be observed and yet such studies may mask underlying effects on biodiversity within microbial populations and communities. The types of evidence which are available for determining critical metal concentrations or loadings for microbial processes and populations in agricultural soil are assessed, particularly in relation to the agricultural use of sewage sludge. Much of the confusion in deriving critical toxic concentrations of heavy metals in soils arises from comparison of experimental results based on short-term laboratory ecotoxicological studies with results from monitoring of long-term exposures of microbial populations to heavy metals in field experiments. The laboratory studies in effect measure responses to immediate, acute toxicity (disturbance) whereas the monitoring of field experiments measures responses to long-term chronic toxicity (stress) which accumulates gradually. Laboratory ecotoxicological studies are the most easily conducted and by far the most numerous, but are difficult to extrapolate meaningfully to toxic effects likely to occur in the field. Using evidence primarily derived from long-term field experiments, a hypothesis is formulated to explain how microorganisms may become affected by gradually increasing soil metal concentrations and this is discussed in relation to defining “safe” or “critical” soil metal loadings for soil protection.

Toxicity of heavy metals to microorganisms and microbial processes in agricultural soils: a review.

Preface.- Contributors.- List of Abbreviations.- Section 1: Basic Principles: Introduction.-Sources of Heavy Metals and Metalloids in Soils.- Chemistry of Heavy Metals and Metalloids in Soils.- Methods for the Determination of Heavy Metals and Metalloids in Soils.- Effects of Heavy Metals and Metalloids on Soil Organisms.- Soil-Plant Relationships of Heavy Metals and Metalloids.- Heavy Metals and Metalloids as Micronutrients for Plants and Animals.-Critical Loads of Heavy Metals for Soils.- Section 2: Key Heavy Metals And Metalloids: Arsenic.- Cadmium.- Chromium and Nickel.- Cobalt and Manganese.- Copper.-Lead.- Mercury.- Selenium.- Zinc.- Section 3: Other Heavy Metals And Metalloids Of Potential Environmental Significance: Antimony.- Barium.- Gold.- Molybdenum.- Silver.- Thallium.- Tin.- Tungsten.- Uranium.- Vanadium.- Glossary of Specialized Terms.- Index.

Heavy metals in soils : trace metals and metalloids in soils and their bioavailability

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1133&context=agronomyfacpub

Nitrogen uptake, fixation and response to fertilizer N in soybeans: A review

The use of plants and associated microorganisms to remove, contain, inactivate, or degrade harmful environmental contaminants (generally termed phytoremediation) and to revitalize contaminated sites is gaining more and more attention. In this review, prerequisites for a successful remediation will be discussed. The performance of phytoremediation as an environmental remediation technology indeed depends on several factors including the extent of soil contamination, the availability and accessibility of contaminants for rhizosphere microorganisms and uptake into roots (bioavailability), and the ability of the plant and its associated microorganisms to intercept, absorb, accumulate, and/or degrade the contaminants. The main aim is to provide an overview of existing field experience in Europe concerning the use of plants and their associated microorganisms whether or not combined with amendments for the revitalization or remediation of contaminated soils and undeep groundwater. Contaminations with trace elements (except radionuclides) and organics will be considered. Because remediation with transgenic organisms is largely untested in the field, this topic is not covered in this review. Brief attention will be paid to the economical aspects, use, and processing of the biomass. It is clear that in spite of a growing public and commercial interest and the success of several pilot studies and field scale applications more fundamental research still is needed to better exploit the metabolic diversity of the plants themselves, but also to better understand the complex interactions between contaminants, soil, plant roots, and microorganisms (bacteria and mycorrhiza) in the rhizosphere. Further, more data are still needed to quantify the underlying economics, as a support for public acceptance and last but not least to convince policy makers and stakeholders (who are not very familiar with such techniques).

Phytoremediation of contaminated soils and groundwater: lessons from the field

Remediation technologies for heavy metal contaminated groundwater.

Phytoextraction of heavy metals by canola (Brassica napus) and radish (Raphanus sativus) grown on multicontaminated soil.

In this work we studied the influence of Pb, Zn, and Tl on microbial biomass survival and activity during a laboratory incubation of soil. In comparison to uncontaminated soil, the microbial biomass C decreased sharply in soil contaminated with Zn and Tl, whereas the addition of Pb did not have any significant inhibitory effect on the level of microbial biomass C. Zn displayed the greatest biocidal effect, confirmed by the measurement of the death rate quotient (q D). The microbial activity, measured as CO2 evolution, increased significantly in contaminated soils, emphasizing the need of living organisms to expend more energy to survive. The greater demand for energy by microorganisms in order to cope with the toxicity of pollutants was also confirmed by measurement of the metabolic quotient (q CO2). In order to determine whether soil microorganisms affect the bioavailability of these metals through their mobilization and release, we studied the relationships between available Pb, Zn, and Tl, and microbial biomass C. The water-soluble fraction of Tl, available Tl, and Zn, and microbial biomass C were related significantly, but not Pb.

Bioavailability and effects of heavy metals on soil microbial biomass survival during laboratory incubation

Removal of trace metals by Sorghum bicolor and Helianthus annuus in a site polluted by industrial wastes: a field experience.

Soils polluted by heavy metals can be reclaimed using a number of expensive tactics that either remove the contaminants or stabilize them within the soil. The value of metal accumulating plants for environmental remediation has recently been appreciated and promising results have been obtained. This paper reports a study on the behavior of Brassica napus, Brassica juncea, Raphanus sativus and Brassica carinata grown on a substrate contaminated by several heavy metals caused by the use of contaminated irrigation water. Data on carbon dioxide assimilation, biomass growth and the bioconcentration and translocation factor of each metal in each species were measured. The polluted substrate caused only a small variation in photosynthesis, however transpiration was more affected by the experimental substrate and in all three species of the genus Brassica the presence of metals in the substrate resulted in higher transpiration levels.

G. Zerbi

Papers

Phytoextraction of heavy metals by canola (Brassica napus) and radish (Raphanus sativus) grown on multicontaminated soil.

Bioavailability and effects of heavy metals on soil microbial biomass survival during laboratory incubation

Removal of trace metals by Sorghum bicolor and Helianthus annuus in a site polluted by industrial wastes: a field experience.

Reclamation of polluted soil: phytoremediation potential of crop-related brassica species

The application of phytoremediation technology in a soil contaminated by pyrite cinders