Indoor use of pest control products containing fipronil has resulted in detection of fiproles in wastewater. In a recent study of a municipal wastewater treatment plant , fipronil was detected at an average daily concentration of 17-31 ng L-1 and 13- 21 ng L-1 in raw sewage and treated effluent, respectively. A regional study of WWTPs in northern California revealed 100% detection frequency of fipronil, fipronil sulfone, and fipronil sulfide in influent and effluent samples. In the same study, fipronil and fipronil sulfone influent concentrations were 8.6-74.9 ng L-1 and 1.1-11.9 ng L-1, respectively, while effluent concentrations were 14.3- 48.6 ng L-1 and 1.1-16.3 ng L-1, respectively. Clearly, conventional WWTPs are ineffective in removing fiproles emanating from indoor pest control product applications. There is a great deal of evidence regarding the toxicity of fiproles to a variety of non-target aquatic organisms. Several studies have documented LC50 acute toxicity values for fipronil, with representative values including 320 ng L-1 for grass shrimp , 140 ng L-1 for mysid shrimp , and 180-310 ng L-1 for the black fly. A particularly sensitive species,Chironomus dilutus, exhibited a mean 96 h EC50 value of 32.5 ng L-1 for fipronil and 7-10 ng L-1 for its degradation products. Since fipronil’s degradation products can elicit toxicity that is equal to or greater than the parent compound, it is necessary to include them in this research. Evidently, sensitive aquatic organisms are at risk of experiencing adverse effects as a result of exposure to fiproles at environmentally relevant concentrations,ebb flow table which may elicit lethality or effects that otherwise compromise their survivability.

Synthetic pyrethroid insecticides are widely used, by professionals and consumers alike, to combat urban and agricultural pests. Insecticides that belong to the pyrethroid class are utilized for structural pest control and serve as the active ingredients in many consumer pesticide products. A survey of California home improvement stores conducted in 2010 found that 46% of insecticide products contained at least one pyrethroid. In addition, it has been estimated that pyrethroids constitute up to 74% of pesticide use in urban environments. Common pyrethroid active ingredients include bifenthrin, cyfluthrin, deltamethrin, esfenvalerate, lambda-cyhalothrin, permethrin, fenpropathrin, and cypermethrin; bifenthrin and cyfluthrin were selected for consideration in this dissertation. Since pyrethroids are the dominant active ingredients in retail pest control products, the actual urban use of these insecticides is likely much greater. Pyrethroids exert their toxic effects via interaction with voltage-gated sodium channels in the nervous systems of sensitive organisms, which induces neural hyperexcitation and death. Pyrethroid insecticides are highly hydrophobic, with log KOW values ranging from 5.7-7.6. In addition, these compounds exhibit low water solubility and relatively low vapor pressure values. It is therefore likely that the fate of pyrethroids in urban settings is dictated by their hydrophobicity, which ensures that the majority of pyrethroid residues in the environment are found adsorbed to sediments or other solid phases. However, levels of these compounds sufficient to elicit acute toxicityin aquatic organisms have been reported in water columns of urban streams and in wastewater effluent. The high hydrophobicity of pyrethroid insecticides indicates that they undergo sorption to various solids in urban settings following application, which has a profound effect on their subsequent offsite transport.

Concrete surfaces and urban dust particles are of particular importance to the fate of pyrethroids according to previous research. Concrete has been shown to act as a reservoir of applied pesticide residues such as pyrethroids, allowing for gradual desorption during runoff events. Another study of insecticides on concrete surfaces found that the washable fraction of pyrethroids applied as liquid formulations rapidly decreased within the first 7 d of the experiment, suggesting irreversible sorption of pyrethroid residues to the porous concrete interior.A study of residential dust samples detected pyrethroids at higher frequencies than other monitored compounds, with 88% of dust samples containing pyrethroids at concentrations ranging from 5-500 ng g-1. Another study found that more than 80% of pyrethroids present in runoff from concrete surfaces were bound to particles larger than 0.7 µm, and the investigators concluded that pesticide-contaminated particles likely originated from urban dust that was present on concrete surfaces before insecticide treatment. Overall, these data highlight the importance of sorption to solid surfaces in the offsite transport of pyrethroid insecticides. Detections of pyrethroids in runoff and surface water from urban environments are quite frequent as a consequence of outdoor applications of these compounds. One study detected pyrethroids in 100% of samples collected from storm drain outfalls. The same study detected bifenthrin in 96% of samples, with median and maximum concentrations of 5-17 ng L-1 and 73 ng L-1, respectively. The investigators also measured cyfluthrin, permethrin, and cypermethrin at maximum concentrations of 23 ng L-1, 125 ng L-1, and 26 ng L-1, respectively. Another investigation, which focused on creeks of the American River in northern California, observed maximum concentrations of 106.4 ng L-1, 20.5 ng L-1, 9.4 ng L-1, and 21.1 ng L-1 for bifenthrin, cyfluthrin, cypermethrin, and permethrin, respectively. 

A recent monitoring study detected bifenthrin, cyfluthrin, and permethrin in 80%, 40%, and 43%, respectively,hydroponic grow table of samples collected from urban creeks, urban rivers, and storm drain outfalls in Southern California. These observations indicate that outdoor application of pyrethroid formulations results in offsite transport of insecticide residues to surface water. Pyrethroids have been detected in wastewater following down-the-drain washoff of residues applied indoors or infiltration of contaminated surface runoff into wastewater systems. A European study of wastewater treatment systems detected permethrin in secondary treated effluent at a concentration of 20 ± 7 ng L-1. Another study conducted in Europe measured influent and effluent concentrations of permethrin to be 331 ng L-1 and 16 ng L-1, respectively. A Northern California investigation detected bifenthrin, cyfluthrin, cypermethrin,and permethrin in 39%, 6%, 6%, and 33% of wastewater samples, respectively, with maximum observed concentrations of 6.3 ng L-1, 1.7 ng L-1, 17.0 ng L-1, and 17.2 ng L-1 , respectively. More recently, influent from a municipal wastewater treatment plant in San Francisco, California contained bifenthrin, cypermethrin, and cyhalothrin at concentrations of 10-30 ng L-1, 21-44 ng L-1, and 9-31 ng L-1, respectively. The corresponding effluent concentrations were 1-5 ng L-1, 12-45 ng L-1, and 1-5 ng L-1 for bifenthrin, cypermethrin, and cyhalothrin, respectively. Although comparison of the aforementioned influent and effluent measurements indicates that municipal WWTPs are effective in reducing pyrethroid concentrations in wastewater, the reductions are insufficient to eliminate toxic effects in sensitive organisms. Several studies have demonstrated that pyrethroids are very toxic to sensitive aquatic organisms, especially the amphipod Hyalella azteca. Toxicity values for this organism include an EC50 of 3.3 ng L-1 for bifenthrin, a 96 h LC50 of 21.1 ng L-1 for permethrin, and an EC50 of 2.3 ng L-1 for lambda-cyhalothrin.These potent toxicity values are an even greater cause for concern in the presence of pyrethroid mixtures, since there is evidence of additive toxicity. The occurrence data presented above confirm that multiple pyrethroids are often present in urban surface water, which confirms that mixture toxicity will be vital when considering the risk of pyrethroids. The available evidence indicates that sensitive aquatic organisms are at risk of experiencing adverse effects when exposed to pyrethroid insecticides present in urban waters following transport from their outdoor and indoor sites of application. Contamination of surface water by urban insecticides such as fiproles and pyrethroids must be addressed to prevent the ecotoxicological impacts that have been documented to occur following their offsite transport as well as potential human health effects caused by reuse of polluted water resources. Mitigation strategies seek to reduce initial contamination of surface water by identifying major causes of pollution and adjusting application methods or disposal practices to minimize offsite transport. In addition, various treatment approaches have been evaluated to improve the quality of storm water and wastewater before they enter surface water systems. Most types of storm water treatment have been developed more recently, while wastewater treatment is a well-established process in developed countries as well as in many developing nations.

Urban storm water runoff is typically collected in catchment systems and deposited directly into surface water without treatment. However, structures designed to mimic the hydrologic and filtration capacity of predevelopment conditions by slowing and filtering storm water runoff are known as green storm water infrastructure or low impact development systems and are increasing in popularity and prevalence. A key metric for assessing the efficacy of these systems is a reduction in the storm water concentrations of toxic chemicals. Some regions have begun to require the implementation of GSI/LID practices in all new developments while others have instituted financial incentives to encourage developers to install such systems. Types of GSI/LID storm water treatment systems include sedimentation basins, retention ponds, bioretention systems, infiltration basins, media filtration systems, bioswales, and constructed wetlands. Bioswales have been shown to reduce concentrations of several pollutants: a recent study observed reductions of 81%, 81%, 82%, and 74% for suspended solids, metals, hydrocarbons, and pyrethroid insecticides, respectively. The same study found that bioswales reduced runoff toxicity to Hyalella azteca and Chironomus dilutus, the organisms most sensitive to pyrethroids and fiproles, respectively. Another study that evaluated a retrofit bioretention cell for the treatment of parking lot runoff observed mass reductions of sediment, total nitrogen, and total phosphorous >99% each. An investigation of experimental soil bioretention columns containing sand, compost, shredded bark, and drinking water treatment residuals found that the columns reduced the concentrations of Zn, Cu, Ni, Pb, Cd, and total polycyclic aromatic hydrocarbons by 99%, 72%, 31%, 91%, >95%, and 95%, respectively. Furthermore, these columns significantly reduced the observed toxicity in zebra fish following runoff water filtration. A subsequent study observed that identical soil bioretention columns prevented all runoff-induced mortality and sublethal toxicity in coho salmon and reduced metals, PAHs, and organic matter by 30-99%, >92%, and >40% respectively. Overall, the data presented regarding treatment of storm water reveals that such systems are effective in reducing concentrations of many classes of contemporary contaminants. It is thus probable that there exists a treatment technique that is effective in reducing concentrations of fiproles and pyrethroids in storm water as well as their associated toxicities, namely, CWs. Municipal wastewater treatment was developed to remove pollutants such as suspended solids, nutrients, biochemical oxygen demand , and fecal coliforms. However, modern wastewater contains several classes of pollutants that conventional WWTPs were not designed to treat, including pharmaceuticals, personal care products, metals, and pesticides. Recent studies have nonetheless examined the efficacy of WWTPs in removing some of these compounds. A treatment plant in Sacramento, California removed approximately 90% of pyrethroids from wastewater, but effluent concentrations were still sufficient to elicit toxicity in sensitive aquatic invertebrates. A conventional WWTP provided no significant removal of total fiprole compounds despite partially removing 25% of fipronil present in influent; parent compound removal was offset by transformation to other toxic fiproles. The existing data emphasize the fact that traditional WWTPs are inadequate in the treatment of organic micropollutants such as fiproles and pyrethroids. It is therefore clear that additional treatment technologies, like CWs, must be implemented to complement WWTP processes. CWs are utilized to improve water quality via treatment of surface water, storm water, or wastewater. Regarding wastewater treatment, CWs may be implemented as a polishing process for highly treated wastewater effluent or as a sole treatment strategy in areas lacking centralized WWTPs. Studies of storm water treatment using CWs have discovered that concentrations of metals and nutrients are significantly reduced by the process. CWs are also gaining popularity as components of wastewater treatment systems since they can effectively treat the targets of conventional wastewater treatment as well as modern pollutants. A review of CW use for wastewater treatment states that removal efficiencies of 60.7%, 80.7%, 63.2%, 68.1%, 39.4%, 21.1%, and 40.9% were observed for BOD < 40 mg L-1 , BOD > 40 mg L-1, chemical oxygen demand, total suspended solids, total nitrogen, ammonia nitrogen, and total phosphorous, respectively. Additional investigations have revealed that CW treatment reduced Zn concentrations by 72% and 97.3%, depending on the influent concentration. Another review reported highly variable removal of As, with a range of 33-99%.