Effects of a bionematicide 1,4-naphthoquinone solution on soil microbial community assessed by PLFA: Tracing toxicity indicators

Abstract

The worldwide demand on bionematicides is in a growing trend, fueled by environmental concerns with potential negative impacts of synthetic products on ecosystems and non-target organisms, as well as by the need to provide solutions to organic farming management. As such, the main goal of the present study was to evaluate the impact of 1,4-naphthoquinone (NTQ), a nematicidal compound found in natural products such as walnut husk, on soil microbial community (non-target organisms), and determine ecotoxicological indicators in order to follow and quantify the effect of this compound. The effects on diversity and metabolic state of the microbial community were evaluated using a Phospholipid-derived Fatty Acid analysis (PLFA) method. Tests were conducted on a natural uncontaminated soil spiked with a range of NTQ concentrations (up to 768 mg/kg), as well as comparable control solutions containing solubilization enhancer Triton X-100 (TX100). NTQ impacted the soil microbial community, causing significant changes on global PLFA profile at 12 mg/kg, and significant changes on taxonomic biomarker balance at 96 mg/kg. TX100 also caused a significant effect on the global profile, but only at 192 mg/kg NTQ-equivalent. The modifications brought by either compounds were distinct, as different indicators were affected. The effects of NTQ on microbial community were quantifiable for several indicators by calculating half maximal effective concentrations (EC50). The method used proved to be suitable for the assessment of NTQ ecotoxicity in soils.