Diethyl phthalate in compost: ecotoxicological effects and response of the microbial community.

There is a great need to understand the environmental impacts of organic pollutants on soil health. Phthalates are widely used in consumables and can be found extensively. We studied the toxicity of diethyl phthalate (DEP), spiked in a compost plant growth substrate, by means of the acute toxicity Flash test and on the basis of the germination and plant growth of radish seedlings. The response of the microbial community to DEP in the growth substrate was studied by PCR-DGGE (denaturing gradient gel electrophoresis). In the acute toxicity test, DEP was found to be less toxic as a pure compound than when mixed with the compost mixture. This suggests the synergistic effect of unknown toxic compounds or the release of compounds due to DEP addition. The same DEP concentration level in compost substrate induced toxic response in both plant test and microbial community analysis. The diversity of the major microbial community was reduced from a broad community to only 10 major species at toxic concentrations of DEP. Several of the identified microbial species are known to be able to degrade phthalates, which means that the suppression of other microbial species might be due to the substrate availability and toxicity. The major species identified included Sphingomonas sp., Pseudomonas sp., Actinomycetes sp.