Neutral electrolyzed oxidizing water is effective for pre-harvest decontamination of fresh produce.

Pre-harvest sanitization of irrigation water has potential for reducing pathogen contamination of fresh produce. We compared the sanitizing effects of irrigation water containing neutral electrolyzed oxidizing water (EOW) or sodium hypochlorite (NaClO) on pre-harvest lettuce and baby spinach leaves artificially contaminated with a mixture of Escherichia coli, Salmonella Enteritidis and Listeria innocua (~1 × 108 colony-forming units/mL each resuspended in water containing 100 mg/L dissolved organic carbon, simulating a splash-back scenario from contaminated soil/manure). The microbial load and leaf quality were assessed over 7 days, and post-harvest shelf life evaluated for 10 days. Irrigation with water containing EOW or NaClO at 50 mg/L free chlorine significantly reduced the inoculated bacterial load by ≥ 1.5 log10, whereas tap water irrigation reduced the inoculated bacterial load by an average of 0.5 log10, when compared with untreated leaves. There were no visual effects of EOW or tap water irrigation on baby spinach or lettuce leaf surfaces pre- or post-harvest, whereas there were obvious negative effects of NaClO irrigation on leaf appearance for both plants, including severe necrotic zones and yellowing/browning of leaves. Therefore, EOW could serve as a viable alternative to chemical-based sanitizers for pre-harvest disinfection of minimally processed vegetables.

The effect of ultrafiltration process on the fate of antibiotic-related microcontaminants, pathogenic microbes, and toxicity in urban wastewater.

Ultrafiltration (UF) was assessed at chemical, microbiological, genetical and toxicological level and in terms of removing specific antibiotic-related microcontaminants from urban wastewater. The UF capacity to remove various antibiotics (clarithromycin, erythromycin, ampicillin, ofloxacin, sulfamethoxazole, trimethoprim, and tetracycline; [A0] = 100 µg L-1) was optimised with respect to the feed recirculation rate (25-50%) and feed/transmembrane pressure (1.5-3/1.5-2.4 bar, respectively). Here, we tested the UF capacity to reduce the cultivable bacteria (faecal coliforms, total heterotrophs, Enterococci, Pseudomonas aeruginosa), enteric opportunistic pathogens, including antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs) load. Moreover, the toxicity towards Daphnia magna and three plant species was investigated. Upon optimisation of UF, the removal of antibiotics ranged from 19% for trimethoprim to 95% for clarithromycin. The concentration of cultivable faecal coliforms in the permeate was significantly reduced compared to the feed (P < 0.001), whereas all the bacterial species decreased by more than 3 logs. A similar pattern of reduction was observed for the ARGs (P < 0.001) and enteric opportunistic pathogens (~3-4 logs reduction). A nearly complete removal of the antibiotics was obtained by UF followed by granular activated carbon adsorption (contact time: 90 min), demonstrating the positive contribution of such combination to the abatement of chemical microcontaminants.

Inactivation, removal, and regrowth potential of opportunistic pathogens and antimicrobial resistance genes in recycled water systems.

With two thirds of the global population living in areas affected by water scarcity, wastewater reuse is actively being implemented or explored by many nations. There is a need to better understand the efficacy of recycled water treatment plants (RWTPs) for removal of human opportunistic pathogens and antimicrobial resistant microorganisms. Here, we used a suite of probe-based multiplex and SYBR green real-time PCR assays to monitor enteric opportunistic pathogens (EOPs; Acinetobacter baumannii, Arcobacter butzlieri, Escherichia coli, Enterococcus faecalis, Klebsiella pneumoniae, Legionella spp., Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Enteritidis, Streptococcus spp.) and antimicrobial resistance genes (ARGs; qnrS, blaSHV, blaTEM, blaGES, blaKPC, blaIMI, blaSME, blaNDM, blaVIM, blaIMP, blaOXA-48-like, mcr-1 and mcr-3) of key concern from an antimicrobial resistance (AMR), waterborne and foodborne disease perspective. The class 1 integron-integrase gene (intl1) was quantified as a proxy for multi-drug resistance. EOPs, intl1 and ARGs absolute abundance (DNA and RNA) and metabolic activity (RNA) was assessed through three RWTPs with differing treatment trains. Our results indicate that RWTPs produced high quality recycled water for non-potable reuse by removing >95% of EOPs and ARGs, however, subpopulations of EOPs and ARGs survived disinfection and demonstrated potential to become actively growing members of the recycled water and distribution system microbiomes. The persistence of functional intl1 suggests that significant genetic recombination capacity remains in the recycled water, along with the likely presence of multi-drug resistant bacteria. Results provide new insights into the persistence and growth of EOPs, and prevalence and removal of ARGs in recycled water systems. These data will contribute towards the emerging evidence base of AMR risks in recycled water to inform quantitative risk-based policy development regarding water recycling schemes.

Exploiting the intrinsic microbial degradative potential for field-based in situ dechlorination of trichloroethene contaminated groundwater.

Bioremediation of trichloroethene (TCE) polluted groundwater is challenging, with limited next generation sequencing (NGS) derived information available on microbial community dynamics associated with dechlorination. Understanding these dynamics is important for designing and improving TCE bioremediation. In this study, biostimulation (BS), biostimulation-bioaugmentation (BS-BA) and monitored natural attenuation (MNA) approaches were applied to contaminated groundwater wells resulted in ≥ 95% dechlorination within 7 months. Vinyl chloride's final concentrations in stimulated wells were between 1.84 and 1.87 µg L(-1), below the US EPA limit of 2.0 µg L(-1), compared to MNA (4.3 µg L(-1)). Assessment of the groundwater microbial community with qPCR showed up to ∼ 50-fold increase in the classical dechlorinators' (Geobacter and Dehalococcoides sp.) population post-treatment. Metagenomic assays revealed shifts from Gammaproteobacteria (pre-treatment) to Epsilonproteobacteria and Deltaproteobacteria (post-treatment) only in stimulated wells. Although stimulated wells were functionally distinct from MNA wells post-treatment, substantial dechlorination in all the wells implied some measure of redundancy. This study, one of the few NGS-based field studies on TCE bioremediation, provides greater insights into dechlorinating microbial community dynamics which should be useful for future field-based studies.

Impact of bacterial and fungal processes on 14C-hexadecane mineralisation in weathered hydrocarbon contaminated soil.

In this study, the impact of bacterial and fungal processes on (14)C-hexadecane mineralisation was investigated in weathered hydrocarbon contaminated soil. The extent of (14)C-hexadecane mineralisation varied depending on the bioremediation strategy employed. Under enhanced natural attenuation conditions, (14)C-hexadecane mineralisation after 98 days was 8.5 ± 3.7% compared to <1.2% without nitrogen and phosphorus additions. (14)C-hexadecane mineralisation was further enhanced through Tween 80 amendments (28.9 ± 2.4%) which also promoted the growth of a Phanerochaete chyrsosporium fungal mat. Although fungal growth in weathered hydrocarbon contaminated soil could be promoted through supplementing additional carbon sources (Tween 80, sawdust, compost, pea straw), fungal (14)C-hexadecane mineralisation was negligible when sodium azide was added to soil microcosms to inhibit bacterial activity. In contrast, when fungal activity was inhibited through nystatin additions, (14)C-hexadecane mineralisation ranged from 6.5 ± 0.2 to 35.8 ± 3.8% after 98 days depending on the supplied amendment. Bacteria inhibition with sodium azide resulted in a reduction in bacterial diversity (33-37%) compared to microcosms supplemented with nystatin or microcosms without inhibitory supplements. However, alkB bacterial groups were undetected in sodium azide supplemented microcosms, highlighting the important role of this bacterial group in (14)C-hexadecane mineralisation.

Assessment of five bioaccessibility assays for predicting the efficacy of petroleum hydrocarbon biodegradation in aged contaminated soils.

In this study, the bioaccessibility of petroleum hydrocarbons in aged contaminated soils (1.6-67gkg(-1)) was assessed using four non-exhaustive extraction techniques (100% 1-butanol, 100% 1-propanol, 50% 1-propanol in water and hydroxypropyl-ß-cyclodextrin) and the persulfate oxidation method. Using linear regression analysis, residual hydrocarbon concentrations following bioaccessibility assessment were compared to residual hydrocarbon concentrations following biodegradation in laboratory-scale microcosms in order to determine whether bioaccessibility assays can predict the endpoint of hydrocarbon biodegradation. The relationship between residual hydrocarbon concentrations following microcosm biodegradation and bioaccessibility assessment was linear (r(2)=0.71-0.97) indicating that bioaccessibility assays have the potential to predict the extent of hydrocarbon biodegradation. However, the slope of best fit varied depending on the hydrocarbon fractional range assessed. For the C(10)-C(14) hydrocarbon fraction, the slope of best fit ranged from 0.12 to 0.27 indicating that the non-exhaustive or persulfate oxidation methods removed 3.5-8 times more hydrocarbons than biodegradation. Conversely, for the higher molecular weight hydrocarbon fractions (C(29)-C(36) and C(37)-C(40)), biodegradation removed up to 3.3 times more hydrocarbons compared to bioaccessibility assays with the resulting slope of best fit ranging from 1.0-1.9 to 2.0-3.3 respectively. For mid-range hydrocarbons (C(15)-C(28)), a slope of approximately one was obtained indicating that C(15)-C(28) hydrocarbon removal by these bioaccessibility assays may approximate the extent of biodegradation. While this study demonstrates the potential of predicting biodegradation endpoints using bioaccessibility assays, limitations of the study include a small data set and that all soils were collected from a single site, presumably resulting from a single contamination source. Further evaluation and validation is required using soils from a range of hydrocarbon contamination sources in order to develop robust assays for predicting bioremediation endpoints in the field.