DNOC, a model pollutant, adversely affects the potential of soil microbial communities to mineralise the herbicide 2,4-D: an investigation using micro-sampling procedures

The effects of the herbicide, DNOC, 4,6-dinitro-o-cresol, a model pollutant, have been studied by comparing the potential of soil microbial communities present in individual soil aggregates or in larger soil microcosms as samples of soil aggregates to mineralise the herbicide 2,4-D. We have shown that 2-3 mm soil aggregates vary widely in their 2,4-D mineralisation potential and that ageing or exposure to DNOC considerably simplified the distribution patterns of this capacity. The main factors of variation have been quantified and classified using a quasi-likelihood method derived from the Generalised Linear Model approach. Besides DNOC concentration and duration of exposure, an additional ‘rank’ factor reflecting a desiccation gradient of the aggregates on the microtiter plates was found to have statistical significance. We concluded that it should be possible to derive an experimental approach, designated as ‘functional profiling’, with potential use to detect soil chemical contamination. Curves of 2,4-D mineralisation in individual soil aggregates could be classified according to three different types of kinetics, which were assumed to reflect heterogeneous spatial distribution, differences in microbial community composition and varying efficiency of the microbial consortia involved in 2,4-D degradation. Exposure to DNOC considerably simplified the distribution patterns of the different types of kinetics with one type, showing slow rate and low cumulative mineralisation, becoming predominant as ageing, concentration and duration of DNOC exposure increased. We argue on the possible use of ‘kinetic profiling’ as a sensitive bioindicator of soil quality. By comparison, in soil microcosms, 2,4-D mineralisation showed an extra mineralisation potential of 64% over individual aggregates in the control soil and exposure to DNOC was followed by concentration and time-dependent recovery of the 2,4-D mineralisation potential. It is likely that 2 g size soil microcosms gather a larger number of biochemical capacities which could complement each other to increase the potential of soil to mineralise xenobiotic compounds.     

Aleutian Disease (Plasmacytosis) of Mink: II. Responses of Mink to Formalin-Treated Diseased Tissues and to Subsequent Challenge With Virulent Inoculum

An experiment was carried out to examine the responses of Aleutian and standard dark types of mink to inoculations of formalintreated suspensions of tissues of mink with experimentally transmitted plasmacytosis. Control groups of mink received similar injections of normal Aleutian mink tissues or diseased tissues without formalin treatment. A second experiment was conducted to test the formalinized diseased tissue suspension for immunogenic value. Groups of mink which received one, two, or three doses of “vaccine” were later challenged with virulent inocula. Additional groups of mink served as unvaccinated and environmental controls.

Treatment with 0.3% formalin with fine trituration and incubation at 37°C was effective in preventing the development of plasmacytosis in inoculated mink. These mink remained susceptible to subsequent challenge with untreated diseased tissue suspensions. No immunity was demonstrated in the vaccinated mink. Mink inoculated with normal mink tissues did not develop plasmacytosis, nor did uninoculated environmental controls.

     

A methodological approach for ecotoxicological characterization of non-hazardous sediments for their beneficial reuse

Purpose

In France, the beneficial reuse of sediments is conditioned upon a demonstration of environmental acceptability for each scenario. Such evidence has to be provided in application of the NF EN 12920 +A1 standard methodologies. Before the application of risk assessment methodology, the HP14 hazard property must be measured using specific bioassays. However, sediments may have ecotoxicological impacts despite a non-hazardous classification. The application of a battery of bioassays sensitive to non-hazardous sediments could allow to select sediments before choosing the beneficial reuse option.

Materials and methods

First, HP14 methodologies were applied on the studied sediments. These sediments had to be managed on shore according to French legislation. Then, following recommendations from a previous study, other ecotoxicological tests and modified ecotoxicological tests from HP14 methodology were selected. Ostracods mortality and growth tests were selected as a complement because its sensitivity to sediment ecotoxicity is known. To take into account the effects of extraction method and liquid/solid ratio on ecotoxicological impact of sediments, ecotoxicological tests have been applied to percolates. They have been obtained from up-flow percolation tests following the standard NF EN 14405. For each percolate, the rotifer clones reproduction test and the ostracod mortality and growth tests were performed.

Results and discussion

Contaminant analyses of sediments studied reveal differences in contamination between non-hazardous sediments. The majority of ecotoxicological tests carried out in the HP14 test batteries do not differentiate between non-hazardous sediments with low ecotoxicity. However, inhibition of rotifer reproduction and inhibition of plant germination and growth tests can be used. Among the complementary bioassays performed, the ostracods growth inhibition and multigenerational Daphnia reproduction inhibition tests are especially sensitive. Bioassays performed on percolates reveal low ecotoxicities that were not detected with conventional bioassays. For these tests, maximum ecotoxicities are observed on the first percolates for most of the tested sediments, and ecotoxicity effects decrease with the increase in the liquid/solid ratio.

Conclusions

The results enable us to propose a bioassay battery able to highlight the intrinsic toxicity of non-hazardous sediments. This is achieved through bioassays and using up-flow percolation columns to detect low ecotoxicity. This battery can be integrated into the SEDIMATERIAUX approach to ensure the choice of the beneficial reuse option for such sediment. As some of the proposed bioassays remain unsuitable for marine sediments, future studies will adapt the methodology to the presence of marine salts.

     

Use of an avoidance test for the assessment of microbial degradation of PAHs

An avoidance test using the soil springtail Folsomia candida was used to assess changes in contamination levels at low doses of PAHs following incubation with indigenous microflora. A soil from a former coke site was diluted to 1% in an unpolluted soil from the same site, which was used as a control, then both substrates were remoistened to 80% field capacity. The diluted soil was previously shown to be strongly repellent to F. candida, although not toxic. After 2-month incubation at 20 °C, the mixture lost its repellence capacity and became attractive to the test animal, while the global 16 PAHs content had decreased to a great extent (50%). PAH disappearance was linked to the occurrence of indigenous microbiota able to degrade hydrocarbons.