Soil microbial biomass and microbial activities as indicators of heavy metal pollution*

Heavy metals enter the soil through various sources which besides affecting plant growth also affect soil microorganisms and microbial processes responsible for nutrient cycling. Soil microbial properties can be used for monitoring heavy metal pollution. No single microbial parameter can be universally used as an indicator of soil pollution. Microbial activities such as respiration, C and N mineralization, biological N₂ fixation and soil enzymes, can be measured to monitor heavy metal pollution. Combining microbial respiration with microbial biomass measurements seems to be more sensitive to pollution by heavy metals than either of these parameters alone. Measurements like egosterol content and community structure can throw a light on the shift in bacterial to fungal dominance in soil microbial biomass in response to heavy metal stress. Measurements such as microbial biomass carbon as percentage of soil organic carbon can act as an internal control to suggest that ecosystem is being altered by pollutants. Remediation techniques using soil amendments and hyperaccumulator plants can help to restore polluted soils. Development of molecular techniques to study changes in microbial community structure in response to heavy metals is needed.