Behavior of Chromium in Soils: IV. Toxicity to Microorganisms

Abstract

The toxicity of Cr to soil bacterial isolates was studied by measuring turbidity of liquid cultures supplemented with Cr(VI) or Cr(III). Ten to 12 ppm Cr(VI) was found inhibitory to most isolates growing in either a soil‐extract medium and or in a semisynthetic medium. Gram negative bacteria were more affected than gram positive bacteria by Cr(VI) both at this level and at 1 ppm. Toxicity due to Cr(III) was not observed at similar levels.Nellis loam (Typic Eutrochrept) and Hinesburg fine sandy loam (Entic Haplorthod) samples were treated with 10 and 100 ppm Cr(VI) and 100 ppm Cr(III). All three treatments significantly decreased CO2 evolution from that of controls for the 3‐week duration of the experiment. Extractable Cr(VI) in these soils decreased rapidly during this time, indicating that reduction of the added Cr(VI) was occurring.The toxicity of low levels of Cr(VI) to gram negative bacteria in aqueous culture indicates that soil microbial transformations, such as nitrification, may be affected. The fact that both Cr(III) and Cr(VI) inhibited microbial activity in soil shows that more caution may be needed in handling Cr‐containing wastes, regardless of the form of Cr.

Effect of anionic heavy metals on ammonification and nitrification in soil

“…Moreover Cr(3) was found to affect the growth of Azotobacter at a concentration ranging from 25 to 125/zM, that is about 1.3 to 6.5 ppm. Azotobacter is considered to be more sensitive than the microorganisms reported by Ross and BARTLETT (1981).…”

“…On the contrary these three metals seemed to promote ammonification or mineralization during the first or two days of incubation, because the amount of mineralized nitrogen in soils polluted by these metals increased somewhat more than in the control soil during these periods. Ross and BARTLETT (1981) studied the toxicity of Cr to soil bacterial isolates by measuring the turbidity of liquid cultures that contained dichromate and chromium chloride and found that Gram-negative bacteria were more affected than Gram-positive bacteria by dichromate at a concentration of 1 to 12 ppm. They reported also that the toxicity of Cr (3) was not observed at similar levels.…”

Chromium(VI) Resistance and Extracellular Polysaccharide (EPS) Synthesis by Pseudomonas, Stenotrophomonas and Methylobacterium Strains

“…44) Bacterial growth was estimated by measurement of total cellular protein using the Bradford method. 11,[45][46][47] Cell viability also served as a visual check for contamination.…”

White Oak Creek Watershed: Melton Valley Area Remedial Investigation Report, Oak Ridge National Laboratory, Oak Ridge, Tennessee: Volume 3 Appendix C

“…Acid and alkaline phosphatase activities were affected at 1635 ppm in all three soils to about the same degree, but greater inhibition of alkaline phosphatase activity occurred in the soil with the greatest content of organic matter and clay. Ross et al (1981) evaluated the relative toxicities of forms of Cr to respiration of native soil microflora in a loam and a sandy loam soil. Cr (III), tested at only 100 ppm, caused reductions in both soils of 41 and 48%.…”