An analysis of culture-based methods used for the detection and isolation of Salmonella spp., Escherichia coli, and Enterococcus spp. from surface water: A systematic review.

Identification of methods for the standardized assessment of bacterial pathogens and antimicrobial resistance (AMR) in environmental water can improve the quality of monitoring and data collected, support global surveillance efforts, and enhance the understanding of environmental water sources. We conducted a systematic review to assemble and synthesize available literature that identified methods for assessment of prevalence and abundance of bacterial fecal indicators and pathogens in water for the purposes of monitoring bacterial pathogens and AMR. After screening for quality, 175 unique publications were identified from 15 databases, and data were extracted for analysis. This review identifies the most common and robust methods, and media used to isolate target organisms from surface water sources, summarizes methodological trends, and recognizes knowledge gaps. The information presented in this review will be useful when establishing standardized methods for monitoring bacterial pathogens and AMR in water in the United States and globally.

Fixed bed column experiments using cotton gin waste and walnut shells-derived biochar as low-cost solutions to removing pharmaceuticals from aqueous solutions.

Acetaminophen (ACT), sulfapyridine (SPY), ibuprofen (IBP) and docusate (DCT) are pharmaceuticals with widespread usage that experience incomplete removal in wastewater treatment systems. While further removal of these pharmaceuticals from wastewater effluent is desired prior to beneficial reuse, additional treatment technologies are often expensive and energy intensive. This study evaluated the ability of biochar produced from cotton gin waste (CG700) and walnut shells (WS800) to remove four pharmaceuticals (ACT, SPY, IBP, and DCT) from aqueous solution. Physico-chemical properties of the biochars were characterized by Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), and zeta potential. The increased pyrolysis temperature during the production of WS800 led to an increase in the specific surface area and increased dehydration of the biochar represented by the loss of the OH-group. Fixed-bed column experiments were performed to determine the difference in removal efficiency between the biochars and elucidate the effects of biochar properties on the adsorption capacity for the pharmaceuticals of interest. Results showed that CG700 had a greater affinity for removing DCT (99%) and IBP (50%), while WS800 removed 72% of SPY and 68% of ACT after 24 h. Adsorption was influenced by the solution pH, surface area, net charge, and functional groups of the biochars. The mechanisms for removal included pore filling and diffusion, hydrophobic interactions, hydrogen bonding, and π-π electron donor acceptor interactions. To conduct predictive modeling of the column breakthrough curves, the Thomas, Adams-Bohart, and Yoon-Nelson models were applied to the experimental data. Results demonstrated that these models generally provided a poor fit for the description of asymmetrical breakthrough curves. Overall, the results demonstrate that biochars from cotton gin waste and walnut shells could be used as cost-effective, environmentally friendly alternatives to activated carbon for the removal of pharmaceuticals from aqueous solutions.

The dissemination of antibiotics and their corresponding resistance genes in treated effluent-soil-crops continuum, and the effect of barriers.

Irrigation with treated effluent is expanding as freshwater sources diminish, but hampered by growing concerns of pharmaceuticals contamination, specifically antibiotics and resistance determinants. To evaluate this concern, freshwater and effluent were applied to an open field that was treated with soil barriers including plastic mulch together with surface and subsurface drip irrigation, cultivating freshly eaten crops (cucumbers or melons) for two consecutive growing seasons. We hypothesized that the effluent carries antibiotics and resistance determinants to the drip-irrigated soil and crops regardless of the treatment. To test our hypothesis, we monitored for antibiotics abundance (erythromycin, sulfamethoxazole, tetracycline, chlortetracycline, oxytetracycline, amoxicillin, and ofloxacin) and their corresponding resistance genes (ermB, ermF, sul1, tetW, tetO, blaTEM and qnrB), together with class 1 integron (intl1), and bacterial 16S rRNA, in water, soil, and crop samples taken over two years of cultivation. The results showed that an array of antibiotics and their corresponding resistance genes were detected in the effluent but not the freshwater. Yet, there were no significant differences in the distribution or abundance of antibiotics and resistance genes, regardless of the irrigation water quality, or crop type (p > 0.05), but plastic-covered soil irrigated with effluent retained the antibiotics oxytetracycline and ofloxacin (p < 0.05). However, we could not detect significant correlations between the detected antibiotics and the corresponding resistance genes. Overall, our findings disproved our hypothesis suggesting that treated effluent may not carry antibiotics resistance genes to the irrigated soil and crops yet, plastic mulch covered soil retain some antibiotics that may inflict long term contamination.

Occurrence and distribution of antibiotics and corresponding antibiotic resistance genes in different soil types irrigated with treated wastewater.

Diminishing freshwater (FW) supplies necessitate the reuse of treated wastewater (TWW) for various purposes, like irrigation of agricultural lands. However, there is a growing concern that irrigation with TWW may transfer antibiotic resistance genes (ARGs) to the soil and crops. We hypothesized that TWW irrigation would increase the prevalence of antibiotic residues together with the corresponding ARGs in the irrigated soil. We further predicted that soil texture, especially pH, clay content, and organic matter variabilities, would change the antibiotic residues concentrations and thus ARGs dissemination. To test our predictions, three soils types (loamy-sand, loam, and clay) were irrigated with two water types (FW and TWW), over two consecutive seasons. We monitored physico-chemical parameters, the abundance of seven antibiotic residues, and their corresponding ARGs together with class 1 integron (intI1) in 54 water and soil samples collected at the end of the field experiments. The results revealed increase in antibiotics concentrations and ARGs relative abundance in TWW than FW. Yet, in the soil ARGs relative abundances were independent of the irrigation water quality, but dependent on the soil type, especially the clay content. Further, there were no clear associations between the targeted antibiotics or the presence of heavy metals and ARGs' relative abundance in the water or soil samples. Therefore, our results question the link between the discharge of antibiotics and heavy metals, and the dissemination of ARGs in soil environments.

Assessment of Soil to Mitigate Antibiotics in the Environment Due to Release of Wastewater Treatment Plant Effluent.

With low levels of human antibiotics in the environment due to release of wastewater treatment plant (WWTP) effluent, concern is rising about impacts on human health and antibiotic resistance development. Furthermore, WWTP effluent may be released into waterways used as drinking water sources. The aim of this study was to analyze three antibiotics important to human health (sulfamethoxazole, ofloxacin, and trimethoprim) in soil and groundwater at a long-term wastewater reuse system that spray irrigates effluent. Soil samples were collected (i) at a site that had not received irrigation for 7 mo (approximate background concentrations), and then at the same site after (ii) one irrigation event and (iii) 10 wk of irrigation. Water samples were collected three times per year to capture seasonal variability. Sulfamethoxazole was typically at the highest concentrations in effluent (22 ± 3.7 µg L) with ofloxacin and trimethoprim at 2.2 ± 0.6 and 1.0 ± 0.02 µg L, respectively. In the soil, ofloxacin had the highest background concentrations (650 ± 204 ng kg), whereas concentrations of sulfamethoxazole were highest after continuous effluent irrigation (730 ± 360 ng kg). Trimethoprim was only quantified in soil after 10 wk of effluent irrigation (190 ± 71 ng kg). Groundwater concentrations were typically <25 ng L with high concentrations of 660 ± 20 and 67 ± 7.0 ng L for sulfamethoxazole and ofloxacin, respectively. Given that antibiotics interacted with the soil profile and groundwater concentrations were frequently about 1000-fold lower than effluent, soil may be an adequate tertiary treatment for WWTP effluent leading to improved water quality and protection of human health.

Tylosin sorption to diatomaceous earth described by Langmuir isotherm and Freundlich isotherm models.

Tylosin, an antibiotic used for maintaining livestock health, is a macrolide structurally similar to a number of important, often prescribed human antibiotics. Because of this relationship, tylosin presents a potential threat of antimicrobial resistance from environmental buildup. This work investigated tylosin sorption to natural diatomaceous earth product (DE) and the types of physical interactions responsible for sorption. Most sorption processes were best described by the Langmuir model when compared with Freundlich model. Heat of sorption (ΔH) was 1.14 kJ mol-1 indicating a physisorption process. Change in entropy (ΔS) was 119 J mol-1. Sorption was evaluated from aqueous solution with various H+, KCl and Urea concentrations. In 0.01 M phosphate buffer (PB) pH 6.6, a maximum sorption capacity of 15 mg tylosin per g of DE was achieved. Changing the pH to 2.9 or 11.2 resulted in decreased sorption of tylosin (13 and 10 mg g-1, respectively). Addition of 1 M KCl to 0.01 M PB pH 6.6 decreased sorption of tylosin to DE with the maximum binding capacity of 7 mg g-1. Sorption in 1.0 M urea, 0.01 M phosphate buffer pH 6.6 showed a maximum sorption of 13 mg g-1. Based on these results, the sorption of tylosin appears to be a physisorption process, with charge-charge interactions being the mode of sorption at neutral pH and small contributions from secondary interactions. This information will be useful for developing effective strategies for mitigating tylosin and other antimicrobial's impact on the environment.

Nitrogen Management Affects Nitrous Oxide Emissions under Varying Cotton Irrigation Systems in the Desert Southwest, USA.

Irrigation of food and fiber crops worldwide continues to increase. Nitrogen (N) from fertilizers is a major source of the potent greenhouse gas nitrous oxide (NO) in irrigated cropping systems. Nitrous oxide emissions data are scarce for crops in the arid western United States. The objective of these studies was to assess the effect of N fertilizer management on NO emissions from furrow-irrigated, overhead sprinkler-irrigated, and subsurface drip-irrigated cotton ( L.) in Maricopa, AZ, on Trix and Casa Grande sandy clay loam soils. Soil test- and canopy-reflectance-based N fertilizer management were compared. In the furrow- and overhead sprinkler-irrigated fields, we also tested the enhanced efficiency N fertilizer additive Agrotain Plus as a NO mitigation tool. Nitrogen fertilizer rates as liquid urea ammonium nitrate ranged from 0 to 233 kg N ha. Two applications of N fertilizer were made with furrow irrigation, three applications under overhead sprinkler irrigation, and 24 fertigations with subsurface drip irrigation. Emissions were measured weekly from May through August with 1-L vented chambers. NO emissions were not agronomically significant, but increased as much as 16-fold following N fertilizer addition compared to zero-N controls. Emission factors ranged from 0.10 to 0.54% of added N fertilizer emitted as NO-N with furrow irrigation, 0.15 to 1.1% with overhead sprinkler irrigation, and <0.1% with subsurface drip irrigation. The reduction of NO emissions due to addition of Agrotain Plus to urea ammonium nitrate was inconsistent. This study provides unique data on NO emissions in arid-land irrigated cotton and illustrates the advantage of subsurface drip irrigation as a low NO source system.

Micropollutants in groundwater from septic systems: Transformations, transport mechanisms, and human health risk assessment.

Septic systems may contribute micropollutants to shallow groundwater and surface water. We constructed two in situ conventional drainfields (drip dispersal and gravel trench) and an advanced drainfield of septic systems to investigate the fate and transport of micropollutants to shallow groundwater. Unsaturated soil-water and groundwater samples were collected, over 32 sampling events (January 2013 to June 2014), from the drainfields (0.31-1.07 m deep) and piezometers (3.1-3.4 m deep). In addition to soil-water and groundwater, effluent samples collected from the septic tank were also analyzed for 20 selected micropollutants, including wastewater markers, hormones, pharmaceuticals and personal care products (PPCPs), a plasticizer, and their transformation products. The removal efficiencies of micropollutants from septic tank effluent to groundwater were similar among three septic systems and were 51-89% for sucralose and 53->99% for other micropollutants. Even with high removal rates within the drainfields, six PPCPs and sucralose with concentrations ranging from <0.3 to 154 ng/L and 121 to 32,000 ng/L reached shallow groundwater, respectively. The human health risk assessment showed that the risk to human health due to consumption of groundwater is negligible for the micropollutants monitored in the study. A better understanding of ecotoxicological effects of micropollutant mixtures from septic systems to ecosystem and human health is warranted for the long-term sustainability of septic systems.

Septic systems as hot-spots of pollutants in the environment: Fate and mass balance of micropollutants in septic drainfields.

Septic systems, a common type of onsite wastewater treatment systems, can be an important source of micropollutants in the environment. We investigated the fate and mass balance of 17 micropollutants, including wastewater markers, hormones, pharmaceuticals and personal care products (PPCPs) in the drainfield of a septic system. Drainfields were replicated in lysimeters (1.5m length, 0.9m width, 0.9m height) and managed similar to the field practice. In each lysimeter, a drip line dispersed 9L of septic tank effluent (STE) per day (equivalent to 32.29L/m(2) per day). Fourteen micropollutants in the STE and 12 in the leachate from drainfields were detected over eight months. Concentrations of most micropollutants in the leachate were low (<200ng/L) when compared to STE because >85% of the added micropollutants except for sucralose were attenuated in the drainfield. We discovered that sorption was the key mechanism for retention of carbamazepine and partially for sulfamethoxazole, whereas microbial degradation likely attenuated acetaminophen in the drainfield. This data suggests that sorption and microbial degradation limited transport of micropollutants from the drainfields. However, the leaching of small amounts of micropollutants indicate that septic systems are hot-spots of micropollutants in the environment and a better understanding of micropollutants in septic systems is needed to protect groundwater quality.

Uptake of Three Antibiotics and an Antiepileptic Drug by Wheat Crops Spray Irrigated with Wastewater Treatment Plant Effluent.

With rising demands on water supplies necessitating water reuse, wastewater treatment plant (WWTP) effluent is often used to irrigate agricultural lands. Emerging contaminants, like pharmaceuticals and personal care products (PPCPs), are frequently found in effluent due to limited removal during WWTP processes. Concern has arisen about the environmental fate of PPCPs, especially regarding plant uptake. The aim of this study was to analyze uptake of sulfamethoxazole, trimethoprim, ofloxacin, and carbamazepine in wheat ( L.) plants that were spray-irrigated with WWTP effluent. Wheat was collected before and during harvest, and plants were divided into grain and straw. Subsamples were rinsed with methanol to remove compounds adhering to surfaces. All plant tissues underwent liquid-solid extraction, solid-phase extraction cleanup, and liquid chromatography-tandem mass spectrometry analysis. Residues of each compound were present on most plant surfaces. Ofloxacin was found throughout the plant, with higher concentrations in the straw (10.2 ± 7.05 ng g) and lower concentrations in the grain (2.28 ± 0.89 ng g). Trimethoprim was found only on grain or straw surfaces, whereas carbamazepine and sulfamethoxazole were concentrated within the grain (1.88 ± 2.11 and 0.64 ± 0.37 ng g, respectively). These findings demonstrate that PPCPs can be taken up into wheat plants and adhere to plant surfaces when WWTP effluent is spray-irrigated. The presence of PPCPs within and on the surfaces of plants used as food sources raises the question of potential health risks for humans and animals.

Vadose Zone Transport of Natural and Synthetic Estrogen Hormones at Penn State's "Living Filter" Wastewater Irrigation Site.

The increase in endocrine-disrupting compounds in the environment has generated research focused on the behavior of these compounds in natural soil and water ecosystems. To understand how estrogens behave in the soil environment as a result of 25+ yr of wastewater irrigation, soils from Penn State's "Living Filter" wastewater irrigation site were extracted and analyzed for two natural estrogens (17ß-estradiol and estrone) and one synthetic estrogen (17α-ethynylestradiol). Soil estrogen concentrations were compared for two independent variables: type of land cover and sampling time. Soils were sampled from cropped and forested land areas, and soils were sampled 2 d and 3 wk after a single 12-h effluent irrigation event. A nonirrigated control site was sampled to provide natural background data. For 17ß-estradiol, the nonirrigated mean concentration was 0.68 ± 0.11 ng cm, and the irrigated values, including samples from both land areas and time frames, ranged from 0.99 ± 0.11 to 1.82 ± 0.69 ng cm. For estrone, the nonirrigated mean concentration was 2.36 ± 0.22 ng cm, and the irrigated values, including samples from both land areas collected and time frames, ranged from 2.18 ± 0.20 to 6.24 ± 3.14 ng cm. The 17α-ethynylestradiol nonirrigated mean concentration was 0.47 ± 0.40 ng cm. The irrigated values, including samples from both land areas and time frames, ranged from 0.25 ± 0.06 to 1.37 ± 0.39 ng cm. This study found that time of sampling, land cover, and irrigation can affect estrogen concentrations in soils, resulting in levels that exceed natural background and require improvements in management practices.

Assessing environmental impacts of treated wastewater through monitoring of fecal indicator bacteria and salinity in irrigated soils.

To assess the potential for treated wastewater irrigation to impact levels of fecal indicator bacteria (FIB) and salinity in irrigated soils, levels of Escherichia coli, Enterococcus, and environmental covariates were measured in a treated wastewater holding pond (irrigation source water), water leaving the irrigation system, and in irrigated soils over 2 years in a municipal parkland in Arizona. Higher E. coli levels were measured in the pond in winter (56 CFU 100 mL(-1)) than in summer (17 CFU 100 mL(-1)); however, in the irrigation system, levels of FIB decreased from summer (26 CFU 100 mL(-1)) to winter (4 CFU 100 mL(-1)), possibly related to low winter water use and corresponding death of residual bacteria within the system. For over 2 years, no increase in FIB was found in irrigated soils, though highest E. coli levels (700 CFU g(-1) soil) were measured in deeper (20-25 cm) soils during summer. Measurements of water inputs vs. potential evapotranspiration indicate that irrigation levels may have been sufficient to generate bacterial percolation to deeper soil layers during summer. No overall increase in soil salinity resulting from treated wastewater irrigation was detected, but distinct seasonal peaks as high as 4 ds m(-1) occurred during both summers. The peaks significantly declined in winter when surface ET abated and more favorable water balances could be maintained. Monitoring of seasonal shifts in irrigation water quality and/or factors correlated with increases and decreases in FIB will aid in identification of any public health or environmental risks that could arise from the use of treated wastewater for irrigation.

Seasonal variation in accurate identification of Escherichia coli within a constructed wetland receiving tertiary-treated municipal effluent.

As the reuse of municipal wastewater escalates worldwide as a means to extend increasingly limited water supplies, accurate monitoring of water quality parameters, including Escherichia coli (E. coli), increases in importance. Chromogenic media are often used for detection of E. coli in environmental samples, but the presence of unique levels of organic and inorganic compounds alters reclaimed water chemistry, potentially hindering E. coli detection using enzyme-based chromogenic technology. Over seven months, we monitored E. coli levels using m-Coli Blue 24 broth in a constructed wetland filled with tertiary-treated municipal effluent. No E. coli were isolated in the wetland source waters, but E. coli, total coliforms, and heterotrophic bacteria increased dramatically within the wetland on all sampling dates, most probably due to fecal inputs from resident wildlife populations. Confirmatory testing of isolates presumptive for E. coli revealed a 41% rate of false-positive identification using m-Coli Blue 24 broth over seven months. Seasonal differences were evident, as false-positive rates averaged 35% in summer, but rose sharply to 75% in the late fall and winter. Corrected E. coli levels were significantly correlated with electrical conductivity, indicating that water chemistry may be controlling bacterial survival within the wetland. This is the first study to report that accuracy of chromogenic media for microbial enumeration in reclaimed water may show strong seasonal differences, and highlights the importance of validation of microbiological results from chromogenic media for accurate analysis of reclaimed water quality.