Effect of Biofumigants on Soil Microbial Communities and Ecotoxicology of Earthworms (Eisenia andrei) Tanya Fouché & Mark Maboeta & Sarina Claassens Received: 4 April 2016 /Accepted: 28 June 2016 # Springer International Publishing Switzerland 2016 Abstract Biofumigation is considered a good alterna- tive to chemical fumigation because it can control crop pathogens and diseases with lower health and environ- mental risks than chemical fumigants. Glucosinolates are volatile compounds found in most Brassica species, and when hydrolysed, it forms a range of natural toxins including isothiocyanates that act as biofumigants. However, the effect of glucosinolates and their break- down products on non-target and beneficial soil organ- isms is not well documented. Three biofumigants, broc- coli, mustard and oilseed radish, were evaluated for their effect on earthworms (Eisenia andrei) and the soil mi- crobial community. Sub-lethal endpoints, including growth and reproductive success of the earthworms, were monitored. Genotoxicity of the biofumigants to- wards earthworms was evaluated by means of the comet assay. Broccoli reduced earthworm reproduction while mustard induced more DNA strand breaks in earthworm cells compared to the control. Soil microbial community function and structure were evaluated by means of com- munity level physiological profiling and phospholipid fatty acid analyses. The effects exerted by the biofumigants on the microbial community were the most pronounced within the first 14 days after applica- tion. Carbon substrate utilisation was most affected by the oilseed radish treatment and microbial community structure by the mustard treatment. Keywords Biofumigation . Biolog™ . Comet assay . Eisenia andrei . Microbial community . Phospholipid fatty acid 1 Introduction Concerns about the extensive use and negative environ- mental effects of chemical fumigants have led to more research on biofumigation (Lazzeri et al. 2004). Crop residues of Brassica species such as mustard (Brassica juncea) and broccoli (Brassica oleracea) are high in volatile glucosinolates; once incorporated into the soil as green manure, they act as biofumigants (Brown and Morra 1997). When the glucosinolates come in contact with the enzyme myrosinase, also contained in the plant cell, it is hydrolysed and releases natural and biological- ly active compounds including isothiocyanates (ITCs), thiocyanates and nitriles (Kirkegaard et al. 2004). Sev- eral studies have confirmed the effectiveness of these natural toxins, especially ITCs, as fungicidal, bacteri- cidal and/or nematicidal products against a series of plant pests, for example crown rot, wilt and root-knot nematodes of corn and wheat crops (Brown and Morra 1997; Kirkegaard et al. 2004; Henderson et al. 2009). Biofumigation is an important crop protection practice in commercial and emerging agriculture because it can control agricultural crop pathogens and diseases without the health and environmental risks associated with chemical fumigants (Brown and Morra 1997; Potgieter et al. 2013). However, little is known about the effects of glucosinolates and its breakdown products on non-target Water Air Soil Pollut (2016) 227:256 DOI 10.1007/s11270-016-2960-6 T. Fouché : M. Maboeta : S. Claassens (*) Unit for Environmental Sciences and Management, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa e-mail: sarina.claassens@nwu.ac.za