Biodegradation of the Insecticide N,N-Diethyl-m-Toluamide by Fungi: Identification and Toxicity of Metabolites

Chung-Ang University, Sŏul, Seoul, South Korea
Archives of Environmental Contamination and Toxicology (Impact Factor: 1.9). 05/2005; 48(3):323-8. DOI: 10.1007/s00244-004-0029-9
Source: PubMed


Fungi (Cunninghamella elegans ATCC 9245, Mucor ramannianus R-56, Aspergillus niger VKMF-1119, and Phanerochaete chrysosporium BKMF-1767) were tested to elucidate the biologic fate of the topical insect repellent N,N-diethyl-m-toluamide (DEET). The elution profile obtained from analysis by high-pressure liquid chromatography equipped with a reverse-phase C-18 column, showed that three peaks occurred after incubation of C. elegans, with which 1 mM DEET was combined as a final concentration. The peaks were not detected in the control experiments with either DEET alone or tested fungus alone. The metabolites produced by C. elegans exhibited a molecular mass of 207 with a fragment ion (m/z) at 135, a molecular mass of 179 with an m/z at 135, and a molecular mass of 163 with an m/z at 119, all of which correspond to N,N-diethyl-m-toluamide-N-oxide, N-ethyl-m-toluamide-N-oxide, and N-ethyl-m-toluamide, respectively. M. ramannianus R-56 also produced N, N-diethyl-m-toluamide-N-oxide and N-ethyl-m-toluamide but did not produce N-ethyl-m-toluamide-N-oxide. For the biologic toxicity test with DEET and its metabolites, the freshwater zooplankton Daphnia magna was used. The biologic sensitivity in decreasing order was DEET > N-ethyl-m-toluamide > N,N-diethyl-m-toluamide-N-oxide. Although DEET and its fungal metabolites showed relatively low mortality compared with other insecticides, the toxicity was increased at longer exposure periods. These are the first reports of the metabolism of DEET by fungi and of the biologic toxicity of DEET and its fungal metabolites to the freshwater zooplankton D. magna.

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    • "Results of this study suggest that DEET is moderately toxic in the aquatic environment, since estimated values of 48 h LC 50 (95% CI) for S. vittatum were 80.12 mg/L (53.53e106.71). S. vittatum showed to be a more sensitive species when compared to the crustacean Daphnia magna (48 h LC 50 ¼ 160 mg/L DEET) (Seo et al., 2005) and to fish species such as Gambusia affinis (48 h LC 50 ¼ 235 mg/L) (Michael and Grant, 1974) and Oncorhynchus mykiss (96 h LC 50 ¼ 71.3 mg/L) (USEPA, 1998). Since DEET affects gustatory and olfactory receptors of insects, our results seems to confirm that DEET can act as a feeding deterrent since S. vittatum larvae exposed to DEET showed feeding inhibition (Fig. 1 "
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    ABSTRACT: Stream ecosystems face ever-increasing pressures by the presence of emergent contaminants, such as, personal care products. N, N-diethyl-3-methylbenzamide (DEET) is a synthetic insect repellent that is being found in surface waters environments in concentrations up to 33.4 μg/L. Information concerning DEET's toxicity in the aquatic environment is still limited and focused only on its acute effects on model species. Our main objective was to assess the effects of DEET exposure to a caddisfly non-target species using sub-lethal endpoints. For that, we chose Sericostoma vittatum, an important shredder in Portuguese freshwaters that has been already used in different ecotoxicological assays. Besides acute tests, S. vittatum were exposed during 6 days to a gradient of DEET concentrations (8, 18 and 40.5 mg/L) to assess effects on feeding behaviour and biochemical responses, such as, lipid peroxidation levels (LPO), catalase and acetylcholinesterase (AChE) activities, and also assess effects on energy reserves and consumption. Acute tests revealed a 48 h-LC50 of 80.12 mg/L and DEET exposure caused feeding inhibition with a LOEC of 36.80 mg/L. Concerning the biochemical responses, DEET caused no effects in LPO nor on catalase activity. A non-significant decrease in AChE activity was observed. Regarding energetic reserves, exposure to DEET caused a significant reduction in S. vittatum carbohydrates levels. These results add important information for the risk assessment of insect repellents in the aquatic environment and suggest that reported environmental concentrations of DEET are not toxic to non-target freshwater insects.
    Full-text · Article · Apr 2016 · Chemosphere
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    • "N,N-Diethyl-m-toluamide (DEET; CAS # 134-62-3) has been used extensively as an insect repellent around the world since its invention in 1946 (Sax and Lewis 1989). Despite 6 decades of research on the mode of action of DEET in haematophagous arthropods, many questions still remain unanswered (Simon 2014). "
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    ABSTRACT: Despite the ubiquitous occurrence of N,N-diethyl-m-toluamide (DEET) in aquatic systems, assessments evaluating the toxicity of DEET on phytoplankton species are summed to a single study on a unicellular green alga. In particular, the toxicological effects of DEET in dinoflagellates are unknown. In this study, we employed the mixotrophic dinoflagellate Gymnodinium instriatum as a study system to evaluate acute effects of DEET on the oxygen flux of laboratory cultures. This study reports an inhibitory reaction model of DEET described by the equation y = 4.99x(0.54), where y represents the percent inhibition of oxygen flux and x represents DEET concentration in mg L(-1) (r(2) = 0.98). Based on this model, the effective concentration of DEET needed to reduce O2 flux by 50 % (EC50) for this species was found to be at 72.9 mg L(-1). The reported EC50 is more than five times lower than the EC50 reported previously for the unicellular green algae Chlorella protothecoides. This study raises the question of the potential toxicological effects of DEET in dinoflagellates, in particular those populations inhabiting systems characterized by low water circulation such as enclosed bays and lagoons.
    Full-text · Article · Oct 2015 · Ecotoxicology
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    • "N,N-diethyl-3-methylbenzamide (DEET) is still considered the best available product, repelling a wide variety of insects, ticks, and mites [8]. Though DEET is not expected to bioaccumulate, the amounts present in the environment have been shown to be toxic to some species of zooplankton and fish [9] [10]. In humans, the repellent may cause insomnia, mood disturbances, impaired cognitive functions, seizures, toxic encephalopathy, and allergic reactions [11] [12] [13]. "
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