Toxicity of density separation media to Escherichia coli and Mycobacterium strain PC01: implications for density-separation of soils and sediments.

Separation of low-density sediment detritus in CsCl solution is a promising technique for benthic studies. The known toxicity of CsCl suggests the possibility of toxicity in the separated sediment. Fluoranthene biodegradation by Mycobacterium strain PC01 was used to probe microbial activity in sediment following density separation. Complete inhibition of biodegradation occurred in sediment previously contacted with CsCl media, but washing eliminated inhibition. Washing may not be preferable for subsequent study of the separated sediment, suggesting the need for less toxic media. We studied how various density separation media affected the viability of Escherichia coli to quantify toxicity. Although all media decreased viability, Nycodenz(R) and metrizamide were one to three orders of magnitude less toxic to bacteria than CsCl or Na2WO4. Toxicity was generally related to ionic strength. These results demonstrate that iodinated benzoic acids are superior to metal salts solutions for preserving biological activity on separated sediment or soil.