Spatial and temporal variability of micropollutants within a wastewater catchment system.

Treated wastewater effluent is a major contributor to concentrations of many anthropogenic chemicals in the environment. Examining patterns of these compounds measured from different catchment areas comprising the influent to a wastewater treatment plant, across many months, may reveal patterns in compound sources and seasonality helpful to management efforts. This study considers a wastewater catchment system that was sampled at six sub-catchment sites plus the treatment plant influent and effluent at seven time points spanning nine months. Wastewater samples were analyzed with LC-QTOF-MS using positive electrospray ionization and GC-QTOF-MS using negative chemical ionization and electron ionization. MS data were screened against spectral libraries to identify micropollutants. As expected, multiple classes of chemicals were represented, including pharmaceuticals, plasticizers, personal care products, and flame retardants. Patterns in the compounds seen at different sampling sites and dates reflect the varying uses and down-the-drain routes that influence micropollutant loading in sewer systems. Patterns in examined compounds revealed little spatial variation, and greater temporal variation. For example, the greatest loads of DEET were found to occur in the summer months. Additionally, groups of compounds exhibited strong correlation with each other, which could be indicative of similar down-the-drain routes (such as a group intercorrelated chemicals that are components of cleaning products) or the influence of similar physicochemical processes within the sewer system. This study contributes to the understanding of dynamics of micropollutants in sewer systems.

Sub-sewershed Monitoring to Elucidate Down-the-Drain Pesticide Sources.

Pesticides have been reported in treated wastewater effluent at concentrations that exceed aquatic toxicity thresholds, indicating that treatment may be insufficient to adequately address potential pesticide impacts on aquatic life. Gaining a better understanding of the relative contribution from specific use patterns, transport pathways, and flow characteristics is an essential first step to informing source control measures. The results of this study are the first of their kind, reporting pesticide concentrations at sub-sewershed sites within a single sewer catchment to provide information on the relative contribution from various urban sources. Seven monitoring events were collected from influent, effluent, and seven sub-sewershed sites to capture seasonal variability. In addition, samples were collected from sites with the potential for relatively large mass fluxes of pesticides (pet grooming operations, pest control operators, and laundromats). Fipronil and imidacloprid were detected in most samples (>70%). Pyrethroids were detected in >50% of all influent and lateral samples. There were significant removals of pyrethroids from the aqueous process stream within the facility to below reporting limits. Imidacloprid and fiproles were the only pesticides that were detected above reporting limits in effluent, highlighting the importance of source identification and control for the more hydrophilic compounds. Single source monitoring revealed large contributions of fipronil, imidacloprid, and permethrin originating from a pet groomer, with elevated levels of cypermethrin at a commercial laundry location. The results provide important information needed to prioritize future monitoring efforts, calibrate down-the-drain models, and identify potential mitigation strategies at the site of pesticide use to prevent introduction to sewersheds.

Comparing imidacloprid, clothianidin, and azoxystrobin runoff from lettuce fields using a soil drench or treated seeds in the Salinas Valley, California.

Neonicotinoid insecticide use has increased over the last decade, including as agricultural seed treatments (application of chemical in a coating to the seed prior to planting). In California, multiple crops, including lettuce, can be grown using neonicotinoid treated seeds or receive a direct neonicotinoid soil application (drenching) at planting. Using research plots, this study compared pesticide runoff in four treatments: (1) imidacloprid seed treatment; (2) clothianidin seed treatment; (3) imidacloprid drench and an azoxystrobin seed treatment; and (4) a control with no pesticidal treatment. Neonicotinoid and azoxystrobin concentrations were measured in surface water runoff during six irrigations events in the 2020 growing seasons. Results showed runoff concentrations up to 1308 (±1200) ng L-1 for imidacloprid drench treatment, 431 (±100) ng L-1 for clothianidin seed treatment, 135 (±60) ng L-1 for imidacloprid seed treatment, and 13 (±10) ng L-1 for azoxystrobin seed treatment (treatments averaged). The percent of applied mass in runoff over the entire sampling period varied by compound; the imidacloprid seed treatment and drench were similar (0.015 and 0.019%, respectively) to the clothianidin seed treatment (0.036%) while the azoxystrobin seed treatment was much higher (15%). Although the proportion of imidacloprid in runoff was similar for imidacloprid treatments, the mass applied during soil drench was > 4x the amount applied from the imidacloprid seed treatment. Surface soils were collected before planting and at the end of the trial. The neonicotinoids were detected in soil throughout the study and average maximum concentrations were 9-13 ng g-1; azoxystrobin was detected in only two soils at concentrations up to 0.57 ng g-1. These results elucidate the comparative mass runoff resulting from planting treated seed and soil drench applications and highlight the value of additional work to characterize off-site transport from the many commodities that may be utilizing treated seeds.

Assessing pesticide uses with potentials for down-the-drain transport to wastewater in California.

Pesticides and degradates are ubiquitously detected in municipal wastewater influent in the United States. However, little detailed information exists on their sources. The aim of this study is to investigate California Pesticide Use Report (PUR) and sales data to identify pesticide uses with a high potential for indoor down-the-drain (DtD) transport. The DtD transport of pesticides could result from direct applications to drains and sewers or through indirect activities such as washing pets, treated textiles, laundries, and cleaning surfaces treated with pesticides. An initial screening on pesticide products registered in California with DtD potentials showed that fipronil, imidacloprid, and seven pyrethroids were pesticides of concern due to the relatively high sales in DtD use patterns and high toxicity to aquatic organisms; and thus prioritized for additional evaluation. Uses and sales data of products containing the selected pesticides were analyzed for mass of active ingredient applied with specific DtD pathways and by different user groups. Professional uses were retrieved from the PUR and consumer uses were estimated by comparing PUR data to sales data. Overall, approximately 38,615 kg fipronil, 44,561 kg imidacloprid, and 240,550 kg pyrethroids were used annually in California from 2011 to 2015 with some likelihoods of DtD transport. The shares of professional use ranged from 56% (cypermethrin) to 98% (cyfluthrin), depending on the pesticide, with the majority of the mass applied in and around structures and for some pesticides (imidacloprid and permethrin) on landscapes as well. The remaining mass was applied by consumers on various DtD sources, including pet treatments (fipronil, imidacloprid, and permethrin), treated textiles (permethrin), indoor-only uses (cypermethrin), and mixed indoor/outdoor or outdoor-only applications (other pyrethroids). Results from this study help elucidate the relative significance of specific DtD pathways and pesticide occurrence in California waste streams.

Fipronil washoff to municipal wastewater from dogs treated with spot-on products.

Fipronil and fipronil degradates have been reported in treated wastewater effluent at concentrations that exceed USEPA Aquatic Life Benchmarks, posing a potential risk to the surface waters to which they discharge. Fipronil is a common insecticide found in spot-on flea and tick treatment products that have the potential for down-the-drain transport and direct washoff into surface water. Volunteers currently treating their dogs with a fipronil-containing spot-on product were recruited. Dogs were washed either 2, 7, or 28days after product application, and rinsate from 34 discrete bathing events were analyzed by LC-MS/MS for fipronil and fipronil degradates (collectively known as fiproles). Total fipronil application dosage ranged from 67.1-410.0mg per dog following manufacturers' recommendation based on dog body weight. Total mass of fiproles measured in rinsate ranged from 3.6-230.6mg per dog (0.2 ̶ 86.0% of mass applied). Average percentage of fiproles detected in rinsate generally decreased with increasing time from initial application: 21±22, 16±13, and 4±5% respectively for 2, 7, and 28days post application. Fipronil was the dominant fiprole, >63% of total fiproles for all samples and >92% of total fiproles in 2 and 7day samples. Results confirm a direct pathway of pesticides to municipal wastewater through the use of spot-on products on dogs and subsequent bathing by either professional groomers or by pet owners in the home. Comparisons of mass loading calculated using California sales data and recent wastewater monitoring results suggest fipronil-containing spot-on products are a potentially important source of fipronil to wastewater treatment systems in California. This study highlights the potential for other active ingredients (i.e., bifenthrin, permethrin, etofenprox, imidacloprid) contained in spot-on and other pet products (i.e., shampoos, sprays) to enter wastewater catchments through bathing activities, posing a potential risk to the aquatic organisms downstream of wastewater discharge.

Passage of fiproles and imidacloprid from urban pest control uses through wastewater treatment plants in northern California, USA.

Urban pest control insecticides-specifically fipronil and its 4 major degradates (fipronil sulfone, sulfide, desulfinyl, and amide), as well as imidacloprid-were monitored during drought conditions in 8 San Francisco Bay (San Francisco, CA, USA) wastewater treatment plants (WWTPs). In influent and effluent, ubiquitous detections were obtained in units of ng/L for fipronil (13-88 ng/L), fipronil sulfone (1-28 ng/L), fipronil sulfide (1-5 ng/L), and imidacloprid (58-306 ng/L). Partitioning was also investigated; in influent, 100% of imidacloprid and 62 ± 9% of total fiproles (fipronil and degradates) were present in the dissolved state, with the balance being bound to filter-removable particulates. Targeted insecticides persisted during wastewater treatment, regardless of treatment technology utilized (imidacloprid: 93 ± 17%; total fiproles: 65 ± 11% remaining), with partitioning into sludge (3.7-151.1 µg/kg dry wt as fipronil) accounting for minor losses of total fiproles entering WWTPs. The load of total fiproles was fairly consistent across the facilities but fiprole speciation varied. This first regional study on fiprole and imidacloprid occurrences in raw and treated California sewage revealed ubiquity and marked persistence to conventional treatment of both phenylpyrazole and neonicotinoid compounds. Flea and tick control agents for pets are identified as potential sources of pesticides in sewage meriting further investigation and inclusion in chemical-specific risk assessments. Environ Toxicol Chem 2017;36:1473-1482. © 2016 SETAC.

Start-up performance of a full-scale riverbank filtration site regarding removal of DOC, nutrients, and trace organic chemicals.

The performance of a full-scale riverbank filtration facility in Colorado was evaluated from initial start-up over a period of seven years including the impact of seasonal variations to determine whether sustainable attenuation of various chemical constituents could be achieved. Both, annual and seasonal average concentrations were determined for several wastewater-derived constituents including dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm, nitrate, phosphate for the years 2006, 2009, 2010, 2012, and trace organic chemicals (TOrC) for years 2009, 2010, and 2012. ANOVA analyses and Student's t-tests were performed to evaluate the consistency of contaminant attenuation at the site. Findings revealed no significant statistical differences for any of the bulk parameters with the exception of phosphate suggesting a highly reliable attenuation of DOC and nitrate from start-up to full-scale performance. Phosphate attenuation, however, exhibited a steady decline, which was likely attributed to exhaustion of sorption sites in the subsurface porous media. The river's flow regime influenced both occurrence levels and attenuation of TOrC during riverbank filtration, i.e. less river discharge resulted in higher TOrC concentrations and lower proportion of river water in the recovered groundwater. Differences in removal performance between annual data sets for caffeine, trimethoprim, sulfamethoxazole, and carbamazepine were caused by variations in the source; concentrations in riverbank filtrate remained similar over several years. The seasonal assessment for TOrC revealed steady or improving removal between winter and summer seasons based on the statistical analysis with atenolol being the only exception likely due to an increased microbial activity at elevated temperatures.

Removal of trace organic chemicals in onsite wastewater soil treatment units: a laboratory experiment.

Onsite wastewater treatment is used by 20% of residences in the United States. The ability of these systems, specifically soil treatment units (STUs), to attenuate trace organic chemicals (TOrCs) is not well understood. TOrCs released by STUs pose a potential risk to downstream groundwater and hydraulically-connected surface water that may be used as a drinking water source. A series of bench-scale experiments were conducted using sand columns to represent STUs and to evaluate the efficacy of TOrC attenuation as a function of hydraulic loading rate (1, 4, 8, 12, and 30 cm/day). Each hydraulic loading rate was examined using triplicate experimental columns. Columns were initially seeded with raw wastewater to establish a microbial community, after which they were fed with synthetic wastewater and spiked with 17 TOrCs, in four equal doses per day, to provide a consistent influent water quality. After an initial start-up phase, effluent from all columns consistently demonstrated >90% reductions in dissolved organic carbon and nearly complete (>85%) oxidation of ammonia to nitrate, comparable to the performance of field STUs. The results of this study suggest STUs are capable of attenuating many TOrCs present in domestic wastewater, but attenuation is compound-specific. A subset of TOrCs exhibited an inverse relationship with hydraulic loading rate and attenuation efficiency. Atenolol, cimetidine, and TCPP were more effectively attenuated over time in each experiment, suggesting that the microbial community evolved to a stage where these TOrCs were more effectively biotransformed. Aerobic conditions as compared to anaerobic conditions resulted in more efficient attenuation of acetaminophen and cimetidine.

Variability of trace organic chemical concentrations in raw wastewater at three distinct sewershed scales.

The site-specific daily fluctuations and scale-dependent variability of influent water quality, particularly concentrations of trace organic chemicals (TOrCs), have not yet been well described. In this study, raw wastewater from three distinct sewershed scales was sampled including a centralized wastewater treatment facility in Boulder, Colorado (population ~125,000) and two decentralized wastewater catchments in Golden, Colorado (clustered system population 400, and septic system population 32). Each site was sampled hourly for 26 h and samples were subsequently analyzed in triplicate for 32 TOrCs using liquid chromatography with tandem mass spectrometry and stable isotope dilution. Detection frequency (DF) of the various TOrCs was positively correlated with sewershed size with the greatest DF of the targeted TOrCs at the Boulder site and with decreasing DF with decreasing sewershed size. Site-specific fluctuations were both scale and compound-specific. The 11 TOrCs detected greater than 75% of the time across all three sites were used to further investigate and quantify variability and to develop a statistical model to investigate the flow-dependence and time-dependence of TOrC variability. Sewershed scale was inversely correlated to variability with coefficients of variation ranging from 0.24 to 0.96, 0.39 to 2.22, and 0.32 to 3.93 for the Boulder, cluster, and septic sites, respectively. A significant linear relationship was observed between concentration and flow and concentration and the concentration at prior time points for most TOrCs at the Boulder site. This suggests less variable influent concentrations result from dispersion and mixing in the conveyance system and a larger number of discrete inputs. A notable exception was the chlorinated flame retardant TCPP, which is likely associated with a high concentration, low-flow industrial input. A significant linear relationship between flow and concentration and sequential time points was not common at the decentralized sites. Scientists and engineers developing decentralized treatment systems must consider a larger range of influent qualities, particularly with respect to TOrCs.