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.

Water Quality Impairments Due to Aquatic Life Pesticide Toxicity: Prevention and Mitigation in California, USA.

The management of pesticides to protect water quality remains a significant global challenge. Historically, despite regulatory frameworks intended to prevent, minimize, and manage off-site movement of pesticides, multiple generations of pesticide active ingredients have created a seemingly unending cycle of pesticide water pollution in both agricultural and urban watersheds. In California, the most populous and most agricultural US state, pesticide and water quality regulators realized in the 1990s that working independently of each other was not an effective approach to address pesticide water pollution. Over the years, these California agencies have developed a joint vision and have continued to develop a unified approach that has the potential to minimize pesticide risks to aquatic life through a combination of prevention, monitoring, and management actions, while maintaining pesticide availability for effective pest control. Key elements of the current California pesticide/water quality effort include: 1) pesticide and toxicity monitoring, coupled with watershed modeling, to maximize information obtained from monitoring; 2) predictive fate and exposure modeling to identify potential risks to aquatic life for new pesticide products when used as allowed by the label or to identify effective mitigation measures; and 3) management approaches tailored to the different pesticide uses, discharge sources, physical environments, and regulatory environments that exist for agricultural runoff, urban runoff, and municipal wastewater. Lessons from this effort may inform pesticide management elsewhere in the world as well as other chemical regulatory programs, such as the recently reformed US Toxic Substances Control Act and California's Safer Consumer Products regulatory program. Environ Toxicol Chem 2020;39:953-966. © 2020 SETAC.

Regulatory Modeling of Pesticide Aquatic Exposures in California's Agricultural Receiving Waters.

For the aquatic exposure assessment of pesticides, the USEPA uses the Variable Volume Water Model (VVWM) to predict the estimated environmental concentrations (EECs) of a pesticide in a water body that receives runoff inputs from the Pesticide Root Zone Model (PRZM). The standard farm pond and additional generalized static and flowing water bodies used in endangered species assessment (aquatic bins) are used by USEPA to model the worst-case aquatic exposure for the nationwide exposure assessment. However, whether or not model results are relevant to state-specific conditions has not been validated. In this study, the USEPA water body scenarios are examined for their capability of providing a conservatively realistic estimate of pesticide aquatic exposures in California's agricultural settings. The sensitivity of modeled EECs to key water body parameters (dimensions, flow, and mass transfer) was explored with a one-at-a-time approach by using the standard farm pond as a baseline. The EECs generated from different USEPA water bodies for the worst-case loading were compared with the monitoring data observed in California's agriculturally influencing water bodies. Results showed that the farm pond EECs well captured the worst-case monitoring data, whereas the aquatic bins EECs, especially the flowing bins, tended to overestimate data. The conceptual model of the standard farm pond was also found to be relevant to the highly vulnerable water bodies in California's agricultural areas. The study confirms that VVWM with the standard farm pond scenario is appropriate for the screening-level regulatory exposure assessment in California's agricultural settings.

A review of diazinon use, contamination in surface waters, and regulatory actions in California across water years 1992-2014.

Diazinon is an organophosphorus insecticide that has been widely used in the USA and in California resulting in contamination of surface waters. Several federal and state regulations have been implemented with the aim of reducing its impact to human health and the environment, e.g., the cancellation of residential use products by the USEPA and dormant spray regulations by the California Department of Pesticide Regulation. This study reviewed the change in diazinon use and surface water contamination in accordance with the regulatory actions implemented in California over water years 1992-2014. We observed that use amounts began declining when agencies announced the intention to regulate certain use patterns and continued to decline after the implementation of those programs and regulations. The reduction in use amounts led to a downward trend in concentration data and exceedance frequencies in surface waters. Moreover, we concluded that diazinon concentrations in California's surface waters in recent years (i.e., water years 2012-2014) posed a de minimis risk to aquatic organisms.

A statistical assessment of pesticide pollution in surface waters using environmental monitoring data: Chlorpyrifos in Central Valley, California.

Pesticides are routinely monitored in surface waters and resultant data are analyzed to assess whether their uses will damage aquatic eco-systems. However, the utility of the monitoring data is limited because of the insufficiency in the temporal and spatial sampling coverage and the inability to detect and quantify trace concentrations. This study developed a novel assessment procedure that addresses those limitations by combining 1) statistical methods capable of extracting information from concentrations below changing detection limits, 2) statistical resampling techniques that account for uncertainties rooted in the non-detects and insufficient/irregular sampling coverage, and 3) multiple lines of evidence that improve confidence in the final conclusion. This procedure was demonstrated by an assessment on chlorpyrifos monitoring data in surface waters of California's Central Valley (2005-2013). We detected a significant downward trend in the concentrations, which cannot be observed by commonly-used statistical approaches. We assessed that the aquatic risk was low using a probabilistic method that works with non-detects and has the ability to differentiate indicator groups with varying sensitivity. In addition, we showed that the frequency of exceedance over ambient aquatic life water quality criteria was affected by pesticide use, precipitation and irrigation demand in certain periods anteceding the water sampling events.

Pesticidal copper (I) oxide: environmental fate and aquatic toxicity.

Besides being a naturally occurring element and an essential micronutrient, copper is used as a pesticide, but at generally higher concentrations. Copper, unlike organic pesticides, does not degrade, but rather enters a complex biogeochemical cycle. In the water column, copper can exist bound to both organic and inorganic species and as free or hydrated copper ions. Water column chemistry affects copper speciation and bioavailability. In all water types (saltwater, brackish water, and freshwater), organic ligands in the water column can sequester the majority of dissolved copper, and therefore, organic ligands play the largest role in copper bioavailability. In freshwater, however, the geochemistry of a particular location, including water column characteristics such as water hardness and pH, is a significant factor that can increase copper bioavailability and toxicity. In most cases, organic ligand concentrations greatly exceed copper ion concentrations in the water column and therefore provide a large buffering capacity. Hence, copper bioavailability can be grossly overestimated if it is based on total dissolved copper (TDCu) concentrations alone. Other factors that influence copper concentrations include location in the water column, season, temperature, depth, and level of dissolved oxygen. For example, concentrations of bioavailable copper may be significantly higher in the bottom waters and sediment pore waters, where organic ligands degrade much faster and dissolved copper is constantly resuspended and recycled into the aquatic system. Aquatic species differ greatly in their sensitivity to copper. Some animals, like mollusks, can tolerate high concentrations of the metal, while others are adversely affected by very low concentrations of copper. Emerging evidence shows that very low, sublethal copper levels can adversely affect the sense of smell and behavior of fish. The developmental stage of the fish at the time of copper exposure is critical to the reversibility of sensory function effects. The fish olfactory system may be the most sensitive structure to copper pollution. The major factors that influence copper-induced toxicity are dissolved organic carbon and water salinity. Dissolved organic carbon reduces copper toxicity by sequestering bioavailable copper and forming organic complexes with it. Salinity, on the other hand, influences copper bioavailability at the biological action site and also affects metal biodistribution and bioaccumulation in the organism. Therefore, the salinity gradient can increase or decrease copper toxicity in different aquatic species. In some killifish, copper may affect different organs at different times, depending on the water salinity. The most studied and best explained copper toxicity mechanisms involve inhibition of key enzymes and disruption of osmoregulation in the gill. Other toxicity mechanisms may involve reactive oxygen species generation and changes of gene transcription in the fish olfactory signaling pathway. More studies are needed to evaluate the potential magnitude of copper remobilization from the sediment that may result from climate change and its effects on surface waters. Moreover, the environmental exposure, fate, and ecotoxicity of emerging metal nanoparticles, including nanocopper, will require additional studies as new forms of copper appear from application of nanotechnology to copper compounds.

Distribution of antifouling biocides in California marinas.

Antifouling biocides are used to prevent the settlement and growth of organisms on submerged surfaces. Irgarol 1051 is currently among the most widely used organic booster biocides worldwide. This study reports Irgarol 1051, its major metabolite M1 (aka GS26575), and diuron concentrations found in selected California marinas. Seasonal water samples (n = 46) were collected during the summer and fall of 2006 from eleven marinas throughout Southern and Northern California. The samples were extracted using solid phase extraction and analysed utilizing liquid chromatography tandem mass spectrometry (LC-MS-MS) with electrospray ionization. All three compounds were detected in all samples, representing a 100% frequency of occurrence and indicating widespread use around the sampled marinas. Irgarol concentrations ranged from 12 to 712 ng L(-1) (average 102 ng L(-1)), M1 concentrations were 1-217 ng L(-1) (average 31 ng L(-1)), and diuron concentrations were 5-27 ng L(-1) (average 13 ng L(-1)). In general, concentrations of both Irgarol (15-712 ng L(-1)) and M1 (1-217 ng L(-1)) were greater in samples collected during the summer, corresponding to the peak of the boating season. The detected diuron concentrations in most cases were greater for fall samples (7-27 ng L(-1)), and probably represented a combination of non-agricultural (rights of way) and agricultural applications of diuron in California. The maximum Irgarol concentration detected in California marinas in summer 2006 (712 ng L(-1)) was five times greater than the Irgarol concentration suggested as the plant toxicity benchmark (136 ng L(-1)). Twenty three percent of samples from California marinas in this study exceeded this benchmark, suggesting that detected Irgarol concentrations may be high enough to cause changes in phytoplankton communities in the sampled marinas.