Applicability of the Caenorhabditis elegans survival, growth and reproduction test to assess the effects of biosolids used in agriculture

Modern high productivity agriculture has led to an impoverishment of nutrients and organic carbon in field soils, and as a consequence plants nutrition complements like fertilisers or wastes have to be used to keep high yield. These complex materials can also be a source of toxicants, depending on their origin, so there is a necessity to assess their environmental effects before field use. In this study, biosolids used in agriculture were tested as a mix with standard soil at different field dose through ecotoxicity test on the nematode Caenorhabditis elegans, endpoints for this organism being survival, growth and reproduction. In order to run these tests we first followed the standardized protocol for sediment and soil testing with C. elegans (ISO 10872, 2010). These results showed that the mixtures could be significantly different according to the type of soil (e.g. two phases system with overlaying water). Indeed, soil moistening in the standardized protocol is based on soil dry weight which means that the same amount of water is added for every soil, regardless of the water holding capacity (WHC) of the samples. Moreover, some biosolids can have a high WHC what increase humidity's differences among soil and soil mixed with biosolids when moistened as recommended by this protocol. To prevent this, improvements of the standardized protocol were developed, in which water addition is based on soil WHC instead of soil dry weight. Moreover, food volume added to the samples was lowered in order to be able to include it in the volume for soil moistening. In this context and in order to validate this new method, comparisons between standardized and optimized protocols were carried out for endpoints responses in five soils with different textures. This optimized protocol was used to assess the effect of different biosolids (limed sludge, manure ...) mixed with standard soil at different field rates and an example for a limed sludge is given. Regarding these results, improvements of the standardized protocol are adapted to assess the effects of these materials on C. elegans

Improvement of the Caenorhabditis elegans growth and reproduction test to assess the ecotoxicity of soils and complex matrices

International audienceA growth and reproduction test using the nematode Caenorhabditis elegans was recently standardized by the International Organization for Standardization (ISO). Performing the ISO 10872 protocol (2010) revealed some drawbacks when applied to soil or soil mixed with complex matrices. The authors propose some modifications to the current protocol to normalize the test conditions. An appropriate range of moisture conditions was determined as a percentage of the water-holding capacity (WHC) of the soil. According to the authors' results, C. elegans tests can be performed in the range of 60% to 100% WHC. To ensure that the modifications of the protocol did not affect the organisms' recovery, extraction ratios for the juveniles were subsequently estimated. The modified protocol was found to be as reliable as the standard one concerning recovery of juveniles (over 80%). The protocol was also applied to several chemicals to investigate their potential as reference chemicals for soil toxicity tests. Boric acid, copper chloride, and nickel sulfate showed deleterious effects in a concentration-dependent manner for the growth and reproduction of C. elegans. Finally, the modified protocol was used to assess the growth and reproduction of C. elegans in soil amended with a limed sewage sludge. The authors conclude that the C. elegans modified protocol is a promising tool for the assessment of soil toxicity as well as the toxicity of mixtures with complex matrices

A bacterium-based contact assay for evaluating the quality of solid samples. Results from an international ring-test.

The contact assay measuring the inhibition of Arthrobacter globiformis dehydrogenase activity as an endpoint to evaluate the toxicity of solid samples was tested in an international ring-test to validate its performance for ISO standardization (ISO/CD 18187). This work reports the results of the ring-test involving 9 laboratories from six countries. At least 8 valid data sets were obtained for each sample and more than three quarters of the participants attained the validity criteria defined in the standard. The coefficient of variation within (CVr) and between (CVR) laboratories was generally on average <15% and <30% for negative and positive controls, respectively. Regarding solid samples, the laboratories provided a similar ranking of the samples based on their toxicity, despite some variation in the LOEC values. The logarithmic within-lab standard deviation <0.50 for soils and <0.25 for wastes evidenced a good repeatability. The between-lab variability assessed by a CVR <30%, minimum-maximum factor <4 and a reproducibility standard deviation (SDR) <0.13 for a great part of the solid samples, confirmed the test reproducibility. Overall, this assay proved to be robust, sensitive and feasible for routine use towards the quality assessment of soils and wastes