Blame It on the Metabolite: 3,5-Dichloroaniline Rather than the Parent Compound Is Responsible for the Decreasing Diversity and Function of Soil Microorganisms.

Pesticides are key stressors of soil microorganisms with reciprocal effects on ecosystem functioning. These effects have been mainly attributed to the parent compounds, while the impact of their transformation products (TPs) has been largely overlooked. We assessed in a meadow soil (soil A) the transformation of iprodione and its toxicity in relation to (i) the abundance of functional microbial groups, (ii) the activity of key microbial enzymes, and (iii) the diversity of bacteria, fungi, and ammonia-oxidizing microorganisms (AOM) using amplicon sequencing. 3,5-Dichloroaniline (3,5-DCA), the main iprodione TP, was identified as a key explanatory factor for the persistent reduction in enzymatic activities and potential nitrification (PN) and for the observed structural changes in the bacterial and fungal communities. The abundances of certain bacterial (Actinobacteria, Hyphomicrobiaceae, Ilumatobacter, and Solirubrobacter) and fungal (Pichiaceae) groups were negatively correlated with 3,5-DCA. A subsequent study in a fallow agricultural soil (soil B) showed limited formation of 3,5-DCA, which concurred with the lack of effects on nitrification. Direct 3,5-DCA application in soil B induced a dose-dependent reduction of PN and NO3--N, which recovered with time. In vitro assays with terrestrial AOM verified the greater toxicity of 3,5-DCA over iprodione. "Candidatus Nitrosotalea sinensis" Nd2 was the most sensitive AOM to both compounds. Our findings build on previous evidence on the sensitivity of AOM to pesticides, reinforcing their potential utilization as indicators of the soil microbial toxicity of pesticides in pesticide environmental risk analysis and stressing the need to consider the contribution of TPs in the toxicity of pesticides on the soil microbial community.IMPORTANCE Pesticide toxicity on soil microorganisms is an emerging issue in pesticide risk assessment, dictated by the pivotal role of soil microorganisms in ecosystem services. However, the focus has traditionally been on parent compounds, while transformation products (TPs) are largely overlooked. We tested the hypothesis that TPs can be major contributors to the soil microbial toxicity of pesticides using iprodione and its main TP, 3,5-dichloroaniline, as model compounds. We demonstrated, by measuring functional and structural endpoints, that 3,5-dichloroaniline and not iprodione was associated with adverse effects on soil microorganisms, with nitrification being mostly affected. Pioneering in vitro assays with relevant ammonia-oxidizing bacteria and archaea verified the greater toxicity of 3,5-dichloroaniline. Our findings are expected to advance environmental risk assessment, highlighting the potential of ammonia-oxidizing microorganisms as indicators of the soil microbial toxicity of pesticides and stressing the need to consider the contribution of TPs to pesticide soil microbial toxicity.

Assessment of the impact of three pesticides on microbial dynamics and functions in a lab-to-field experimental approach.

The toxicity of pesticides on soil microorganisms is as an emerging area of concern. Novel and well-standardized tools could be now used to provide a robust assessment of the ecotoxicity of pesticides on soil microorganisms. We followed a tiered lab-to-field approach to assess the toxicity of three pesticides, widely used at EU level, (chlorpyrifos (CHL), isoproturon (IPU) and tebuconazole (TBZ)) on (i) the abundance of 11 microbial taxa and 8 functional microbial groups via q-PCR and (ii) the activity of enzymes involved in biogeochemical cycles via fluorometric analysis. Correlation of microbial measurements with the concentration of pesticides, and their transformation products (TPs) in soil enabled the identification of the compounds driving the effects observed. At lab tests (×1, ×2 and ×10 the recommended dose), CHL and TBZ significantly reduced the relative abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) which recovered by the end of the study, while all pesticides induced a persistent reduction in the relative abundance of sulfur-oxidizing bacteria (SOB). The two demethylated metabolites of IPU (MD-IPU and DD-IPU) adversely affected P-cycling enzymes and leucine aminopeptidase (Leu). At field tests (×1, ×2 and ×5 the recommended dose), a persistent reduction on the relative abundance of AOA was induced by all pesticides, but only CHL and its hydrolysis product 3,5,6 trichloro-2-pyridynol (TCP) soil levels were negatively correlated with AOA relative abundance. Our findings suggest that ammonia-oxidizing microorganisms constitute the most responsive microbial group to pesticides and could be potential candidates for inclusion in pesticide risk assessment.

Carbon mineralization dynamics in soils amended with meat meals under laboratory conditions.

Meat and bone meal (MBM) is obtained from the wastes produced during slaughtering operations. Its high concentration of N and P makes it interesting as an organic fertiliser but its use in soil has been barely studied previously. In this work four laboratory experiments were performed to study the influence of different variables (MBM composition, rate of application, temperature of incubation and the type of soil) on C mineralization dynamics of MBM in agricultural soils. The total CO2-C evolved (as % of added C) after 2 weeks ranged between 10% and 20%. The kinetics of mineralization were rapid, with C evolved as CO2 within the first 4 days representing more than 50% of total C mineralized. A linear correlation was found between the rate of application (added-C) and CO2-C evolved (r2: 0.997; P<0.001). A temperature coefficient (Q10) was used to assess the difference in biological activity at 5 degrees C intervals. Q10, which ranged from 1.0 to 2.7 (250h), was higher for the lower temperature range (Q10 (15-20 degrees C)>Q10 (20-25 degrees C)) and it was found to be related to the soil properties. Finally, the mineralization process was found to be highly dependent upon the different soil factors, although no simple linear correlation was found between mineralization and soil properties.

Reliability of different sampling densities for estimating and mapping lichen diversity in biomonitoring studies.

Sampling requirements related to lichen biomonitoring include optimal sampling density for obtaining precise and unbiased estimates of population parameters and maps of known reliability. Two available datasets on a sub-national scale in Italy were used to determine a cost-effective sampling density to be adopted in medium-to-large-scale biomonitoring studies. As expected, the relative error in the mean Lichen Biodiversity (Italian acronym: BL) values and the error associated with the interpolation of BL values for (unmeasured) grid cells increased as the sampling density decreased. However, the increase in size of the error was not linear and even a considerable reduction (up to 50%) in the original sampling effort led to a far smaller increase in errors in the mean estimates (<6%) and in mapping (<18%) as compared with the original sampling densities. A reduction in the sampling effort can result in considerable savings of resources, which can then be used for a more detailed investigation of potentially problematic areas. It is, however, necessary to decide the acceptable level of precision at the design stage of the investigation, so as to select the proper sampling density.