The most-probable-number enumeration of dichlobenil and 2,6-dichlorobenzamide (BAM) degrading microbes in Finnish aquifers

Abstract

In groundwater subsurface deposits and a topsoil from five aquifers having 2,6-dichlorobenzamide (BAM) in water, we determined the most-probable-number (MPN) of 2,6-dichlorobenzonitrile (dichlobenil) and metabolite BAM degrading microorganisms. Dichlobenil and BAM were combined nitrogen sources in the MPN tubes, which were scored positive at concentrations <75% after 1 month incubation. Aerobic and anaerobic microbes degrading dichlobenil and BAM were common in samples in low numbers of 3.6-210 MPN g dw(-1). Additional degradation occurred in high MPN dilutions of some samples, the microbial numbers being 0.11-120 x 10(5) MPN g dw(-1). The strains were isolated from low and high dilutions of one deposit, and degradation in pure cultures was confirmed by HPLC. According to the 16S rDNA sequencing, strains were from genera Zoogloea, Pseudomonas, Xanthomonas, Rhodococcus, Nocardioides, Sphingomonas, and Ralstonia. Dichlobenil (45.5 +/- 18.3%) and BAM (37.6 +/- 14%) degradation was low in the MPN tubes. Despite of microbial BAM degradation activity in subsurface deposits, BAM was measured from groundwater.

Intermediate accumulation of metabolites results in a bottleneck for mineralisation of the herbicide metabolite 2,6-dichlorobenzamide (BAM) by Aminobacter spp.

“…BAM has also been detected in other European countries, including Belgium, Italy, Finland and Germany (Limbourg et al 2009;Porazzi et al 2005;Pukkila et al 2009;Wolter et al 2000). Dichlobenil is used worldwide, and considerable interest is presently being given to bioremediation of BAMcontaminated groundwater in view of the costly closure of water supply wells due to exceedance of the EU limit value for pesticides (0.1 μg l −1 ).…”

Influence of organic matter, nutrients, and cyclodextrin on microbial and chemical herbicide and degradate dissipation in subsurface sediment slurries

“…Herbicides are widely used throughout the world, and this has led to their occurrence in the environment. The herbicides atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine), simazine (2,4-bis(ethylamino)-6-chloro-1,3,5-triazine), hexazinone (3-cyclohexyl-6dimethylamino-1-methyl-1,3,5-triazine-2,4-dione), and dichlobenil (2,6-dichlorobenzonitrile), and their degradation products desethylatrazine (2-amino-4-chloro-6-isopropylamino-1,3,5-triazine, DEA), deisopropylatrazine (6-chloro-2-N-ethyl-1,3,5-triazine-2,4-diamine, DIA), desethyldeisopropylatrazine (2-chloro-4,6-amino-1,3,5-triazine, DEDIA), and 2,6dichlorobenzamide (BAM) have been found in groundwater, some commonly (Li et al, 2001;Hildebrandt et al, 2007;Vuorimaa et al, 2007;Holtze et al, 2008;Talja et al, 2008;Pukkila et al, 2009). For instance, atrazine, dichlobenil, and BAM dissipation in groundwater deposits has mostly been slow or nonexistent (Johnson et al, 2003;Talja et al, 2008; Pukkila and Kontro, 2014).…”

Sonication Effects on Atrazine Dissipation in Vadose Zone Sediment Slurries

“…Organic matter released in autoclaving could increase solubility, as humic substances in water increased chlordane solubility [40]. In the sediments of this study, organic matter and element concentrations were quite low, compared to the subsurface deposits [10,28] and materials like biochars [26], which resulted in low atrazine adsorption (1.4 ± 1.2 mg·L −1 ). It is difficult to estimate precisely how much of the difference in atrazine concentrations between the slurries and sterilized slurries was due to autoclaving and how much was due to microbial degradation.…”

“…The slurries were stabilized for 10 days on a shaker as presented above (final atrazine concentration 61.9 ± 8.9 mg·L −1 in atrazine-amended slurries) to allow adsorption to occur and reach the equilibrium stage [26]. The liquid phase was removed, ten-fold serial dilution was performed, and 100 µL was cultivated on mineral agar plates having 33 mg·L −1 of atrazine as a nitrogen source, as presented in Liu et al [27] and Pukkila et al [28]. The colonies were counted after 5 days incubation at the temperature of 21 ± 2 • C. The sediment was extracted as presented below.…”