Project Details Advances on the Assessment of Pesticides' Soil Microbial toxicity: New research and regulatory aspects in light of the recent methodological advances

Project No.: 
Start Date: 
01 June 2015
End Date: 


So far pesticides regulation has overlooked their potential effects on soil microbes (which have a pivotal role in ecosystem functioning). The introduction of advanced well standardized molecular and biochemical tools substantially advanced our knowledge on the off-target effects of pesticides on soil microorganisms. These tools if introduced in future regulatory schemes is expected to provide a comprehensive assessment of pesticides soil microbial toxicity. Thus the project aims to review the current knowledge on soil microbial ecotoxicity of pesticides and propose a regulatory scheme on how pesticide soil microbial ecotoxicity should be assessed. It is expected that the project’s main outcome will stimulate the advancement of pesticide regulatory framework towards a more comprehensive assessment of the impact of pesticides on the diversity and functions of soil microbes.


Upon their application, pesticides interact with soil microbes in contrasting ways: they stimulate proliferation of soil microbes which could utilize pesticides as energy source or induce inhibitory effects on the diversity and/or function of soil microbes. So far pesticides regulation has focused on potential effects on aquatics, birds and mammals while effects on soil microbes (which have a pivotal role in ecosystem functioning) are determined by simple C/N mineralization tests which do not provide a reliable toxicity assessment. In the last 10 years the introduction of advanced biochemical and molecular methods revolutionized our knowledge on the ecological role of soil microbes. This stimulated the production of numerous studies looking into the off-target effects of pesticides on soil microbes using these new methods providing novel insights into pesticide soil microbial toxicity. However, improper experimental planning and the use of methods in a non-standardized mode precluded the elucidation of a solid conclusion and stressed the need for a benchmarking document on this area.

This project will develop such a document: a review article in a journal with high impact on pesticide research, which will summarize current knowledge, list advantages and limitations of methods available and their level of standardization and provide guidelines on proper experimentation, data statistical handling and description of the methodological toolbox available.

It is expected that this project will act as a benchmarking for future revision of the assessment of pesticides soil microbial toxicity in light of the recent methodological advances in this area. Previous relevant activities were presented at the 13th IUPAC Pesticide Chemistry Congress and are supported in EU-funded projects (, while first discussions with EFSA have been done.


August 2018 update – Literature data published up to 31.12.2017 were gathered using mainly SCOPUS and this initial search was supplemented by Google Scholar. Key words utilized were “pesticides”, “soil microbial community”, “soil microorganisms”, ” toxicity”, and “ecotoxicity”. The database developed was recently enriched with relevant literature published by 30.6.2018. In the selection of studies we use experimental plan details to discard, by expert judgment, studies that are not considered of high quality. Studies focusing on (a) microbial endpoints particularly responsive to pesticides and (b) methods that are well standardized in the literature, were prioritized. The data collected were categorized according to the pesticide target group (insecticides, fungicides and herbicides). For all studies we recorded
(a) Pesticide Name
(b) Dose rates: these are presented as absolute values i.e. as mg/kg while a normalization to times the maximum recommended dose rate, for this purpose the rates declared in the GAP documents for the given pesticides were used were available
(c) Method employed to assess the toxicity and level of resolution (low, medium high were declared for biochemical tools (i.e. N or C mineralization test), fingerprinting molecular tools (DGGE, TRFLs, cloning) and advanced molecular tools (q-PCR, NGS) respectively.
(d) Standardization level of the protocol used (OECD, ISO or no standardization)
(d) Toxicity endpoints measured (i.e. effects on key microbial functions like nitrification, denitrification determined as measurements of process rates, as dynamics or activity of relevant microbial groups / effects on the diversity of soil microbial groups). Main functional targets were ammonia oxidizing bacteria/archaea, denititrification-related bacteria, nitrogen-fixing bacteria (N cycle) sulfur-oxidizing-bacteria (S cycle), aromatic compounds degrading bacteria, methanotrophs and methanogens (C cycle). Main structural endpoints were bacteria, fungi, archaea and protozoa
(e) The availability of time series of measurements was recorded in all of these studies and recovery or not of any effects was recorded for each study as : not applicable (where no time series were available / recovery / no recovery. In all cases the duration of the study is reported.
(f) Conclusion of the study: toxicity, toxicity but recovery, no toxicity
(g) Source (publication details).


April 2020 update – These data were presented in the next IUPAC Symposium in Ghent in 2019.
A manuscript for PAC is being prepared and the work will be presented at the IUPAC Congress in Montreal in August 2021.


Feb 2022 update – The literature review has been completed and all data compiled and summarized into a review paper which has been submitted recently to Pure and Applied Chemistry entitled “Pesticide soil microbial toxicity: setting the scene for a new pesticide risk assessment for soil microorganisms”. The report is currently under review.

Page last updated 25 Feb 2022