Total Residual Chlorine Research Articles

Spatio-temporal variability of tastes and odors of drinking water within a distribution system

The threshold of human perception in the detection of tastes and odors (T&O) relating to compounds in drinking water is variable. For example, chlorine can be detected at the ppm level and geosmin can be perceived at the ppt level. In this paper, sensory tests (using a human panel), physicochemical analyses (total and free residual chlorine, temperature, metals, geosmin, and 2-methylisoborneol (2MIB)) and microbiological analyses (algae, Actinomycetes and heterotrophic plate count) were performed for water samples collected during a seventeen-month period at ten different locations of a municipal distribution network of Quebec City (Canada). The results showed that different flavors(1) assessed by a panel and aggregated into global flavor intensity (GFI) vary considerably spatially and seasonally. Multiple regression analysis showed that the factors best explaining the variability of GFI are (in order) the season, the location, the concentration of total residual chlorine and the presence of cyanobacteria. Results also demonstrate that chlorine has a masking effect on other T&O.

A Practical Approach to Meet Total Residual Chlorine Minimization Requirement at CSO Basins – Using Onsite TSS Measurement as a Guidance to Adjust NaOCl Dosage

A Practical Approach to Meet Total Residual Chlorine Minimization Requirement at CSO Basins – Using Onsite TSS Measurement as a Guidance to Adjust NaOCl Dosage

Using Real Time Measurement of Influent Suspended Solids to Minimize Effluent Total Residual Chlorine at a Retention Treatment Basin

Using Real Time Measurement of Influent Suspended Solids to Minimize Effluent Total Residual Chlorine at a Retention Treatment Basin

EFFECT OF ELECTROLYTIC TREATMENT OF BALLAST WATER ON THE CORROSION BEHAVIOR OF 316L STAINLESS STEEL

The introduction of invasive marine species into new environments by the ballast water of ships has been identified as one of the four greatest threats to the world's oceans. Many technologies have been developed for ballast water treatment among which electrolytic treatment method has been taken as the most promising one. However, the corrosion problem of metals in treated seawater was seriously concerned by international maritime organization (IMO) and ship owners, especially the corrosion of 316L stainless steel which is widely used in the monitoring equipments of the ballast system of ships. In this study, the variation of environmental parameters of the seawater before and after electrolytic treatment was monitored. The corrosion behaviors of 316L stainless steel in both natural and treated seawater were investigated by electrochemical methods such as open-circuit potential (EOCP) measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The results showed that the pH value of the seawater increased and the dissolved oxygen content decreased slightly after electrolytic treatment, and the contents of dissolved organic carbon and particulate organic carbon decreased significantly in treated seawater. The corrosion test results showed that the resistance of 316L stainless steel to pitting corrosion was enhanced in treated seawater. Compared to the system in natural seawater, the open-circuit potential of the steel in treated seawater shifted about 0.4 V positively, and charge transfer resistance of the steel greatly increased. The breakdown potential of passivation films in treated seawater positively shifted more than 0.37 V. Our experimental results suggested that the corrosion resistance of 316L stainless steel in treated seawater was improved, which was ascribed to the thickening and compactness of the passivation film formed in treated seawater. It is safe for 316L stainless steel to be used in treated ballast water with the total residual chlorine (TRC) concentration of 9.50 mg/L.

Effects of slightly acidic electrolysed drinking water on mice

Slightly acidic electrolysed (SAE) water is a sanitizer with strong bactericidal activity due to hypochlorous acid. We assessed the safety of SAE water as drinking water for mice at a 5 ppm total residual chlorine (TRC) concentration to examine the possibility of SAE water as a labour- and energy-saving alternative to sterile water. We provided SAE water or sterile water to mice for 12 weeks, during which time we recorded changes in body weight and weekly water and food intakes. At the end of the experiment, all of the subject animals were sacrificed to assess serum aspartate aminotransferase, alanine aminotransferase and creatinine levels and to examine the main organs histopathologically under a light microscope. In addition, we investigated the bacteria levels of both types of water. We found no difference in functional and morphological health condition indices between the groups. Compared with sterile water, SAE water had a relatively higher ability to suppress bacterial growth. We suggest that SAE water at 5 ppm TRC is a safe and useful alternative to sterile water for use as drinking water in laboratory animal facilities.

Swimmers contribute to additional formation of N-nitrosamines in chlorinated pool water

This study aimed to investigate the concentrations of N-nitrosamines in chlorinated indoor pool water and to determine whether swimmers’ bodily inputs of organic and inorganic substances increase those concentrations. Three public indoor pools in Chuncheon, Korea were visited for the purposes of obtaining both source (chlorinated drinking water) and pool water samples and comparing their concentrations of six N-nitrosamines as well as certain water quality parameters. Three N-nitrosamines, specifically Nnitrosomorpholine (NMOR), N-nitrosodimethylamine (NDMA), and N-nitrosodiethylamine (NDEA), could be quantified using high-performance liquid chromatography-fluorescence detection (HPLC-FLD). NDMA, showing average and maximum concentrations of 49.5 and 208 ng L−1, respectively, was the major compound found. Paired t-tests showed significantly higher concentrations of NDMA, total nitrosamines, free residual chlorine, combined residual chlorine (chloramines), total residual chlorine, total nitrogen, dissolved organic carbon, Cl−, NO3−, and SO42− in the pool water than in the source water samples at α=0.01, suggesting that organic and inorganic loads from swimmers might contribute to those elevated N-nitrosamine concentrations.

Evaluation of electrolyzed oxidizing water for phytotoxic effects and pre-harvest management of gray mold disease on strawberry plants

Near neutral (pH = 6.3–6.5) electrolyzed oxidizing water (EO water) has been demonstrated to inactivate fungi in pure culture and to mitigate infection on fruit surfaces. One possible alternative or supplement to traditional pre-harvest crop management practices that currently rely on the use of large quantities of fungicides is near neutral EO water. In the present work, treatment of Botrytis cinerea or Monilinia fructicola with near neutral EO water (50 or 100 ppm total residual chlorine (TRC)) in pure culture resulted in a 10 6 reduction and 100% inactivation as evidenced by negative broth enrichment. When applied in concert with 50 or 100 ppm EO water, treatments of Captan 50WP (captan), Rovral (iprodione), Iprodione 4LAG (iprodione), or Switch 62.5 WDG (cyprodinil and fludioxonil) effectively inhibited fungal growth of B. cinerea as evidenced by a 10 6 reduction on the direct plate and negative broth enrichment. Treatments of Captan 50WG (captan), Rovral (iprodione), Iprodione 4LAG (iprodione), Switch 62.5 WDG (cyprodinil and fludioxonil), Captan 80 WDG (captan), or Captevate (captan and fenhexamide) when applied in concert with 50 or 100 ppm EO resulted in a 10 6 reduction of M. Fructicola and 100% inactivation as evidenced by negative broth enrichment. Strawberry plants sprayed with EO water (pH = 6.3–6.5) at concentrations of 50 and 100 ppm TRC once per week, did not result in significant ( P > 0.05) phytotoxicity relative to a water (0 ppm TRC) treatment. In this study, the application of 100 ppm EO water (pH = 6.3–6.5) twice per week to strawberry plants infected with B. cinerea was more effective ( P ≤ 0.05) than a once per week Captan application and as effective as a once per week captan/once per week EO treatment. The once per week captan/once per week EO treatment was significantly more effective ( P ≤ 0.05) than the captan once per week treatment. Dip treatments of strawberries in near neutral EO solutions (50 and 100 ppm TRC; pH = 6.3–6.5) did not leave a chlorine residue on the fruit relative to a water dip. The results from this study suggest that near neutral EO solutions could be used to manage infection of B. cinerea on strawberry plants in the field and also as a disinfection solution for harvesting equipment, greenhouses, packing houses and in commercial facilities to prevent or manage infections of B. cinerea and M. fructicola.

EFFECT OF ELECTROLYTIC TREATMENT OF BALLAST WATER ON CORROSION BEHAVIOR OF TANK STEEL

In order to regulate discharges of the ships' ballast water and reduce the risk of non-native species introduced from the ballast water,the international maritime organization(IMO) has developed international legislation,the ships' ballast water should be treated before discharge, and electrolysis has been developed as a promising method for ballast water treatment.However, the oxidative species such as Cl_2,HClO and NaClO generated during electrolytic treatment may not only kill the non-native aquatic species but also accelerate the corrosion of the ballast tank steel. In this paper,the effect of the total residual chlorine(TRC) concentration in 3.5%NaCl solution on the corrosion of Q235 steel was studied using mainly the open-circuit potential-time measurement (E_(OC)-t) and electrochemical impedance spectroscopy(EIS).Four TRC concentrations,0,5,10 and 20 mg/L,which are around the concentration proved to be effective for removal of non-native aquatic species,were tested.Both the E_(OC)-t and EIS results suggested that the corrosion of the Q235 steel in 3.5%NaCl solution with or without TRC can be divided into three stages:rapid oxidation of steel, coverage of metal surface by oxide film,and breakdown of the oxide film and initiation of corrosion. The negative shift of E_(OC) and reduction of charge-transfer resistance(R_(ct)) of the steel immersed in the solutions containing low TRC concentrations such as 5 and 10 mg/L demonstrated that the corrosion of steel is slightly enhanced.The enhancement of corrosion is due to the increase of the depolarization concentration present in the solutions.But for solution with higher TRC concentration such as 20 mg/L,both the E_(OC) and R_(ct) increased,suggesting retardation of the corrosion process.The retardation of corrosion can be attributed to the passivation of the steel surface due to the strong oxidation of the active species and the formation of compact corrosion product that covers the corrosion sites.This means that increasing TRC concentration to 20 mg/L does not accelerate the corrosion of the tank steel. Therefore,higher TRC concentration for on-board electrolytic treatment is allowable,which is beneficial for shortening the treating process and improving the removal efficiency.

Trihalomethanes Concentration in Different Components of WaterTreatment Plant and Water Distribution System in the North of Iran

Since the surface water is one of the main potable water resources, the usage of chlorine as a disinfectant has increased. Consequently the production rate of disinfection by-products (DBPs) such as Trihalomethane (THM) compounds has grown dramatically. In this paper the THM S concentration changes in the Sangar Water Treatment Plant (SWTP) and Rasht Water Distribution System (RWDS) is presented. The duration of these monitoring tasks were 6 months in 2007 and samples were collected every 2 weeks. Water samples were collected from five locations at SWTP and RWDS. Some independent variables including Total Organic Carbon (TOC), pH, temperature, and residual chlorine were measured by Pearson method to find a relation between THM S formation and these variables. In the case of TOC, Pearson method showed a corre- lation of r = 0.8096 for SWTP and r = 0.3696 for RWDS between THM formation and TOC. Also the relationship for SWTP was r = 0.239 and r = 0.2336 for RWDS between THM formation and temperature. Correlation between THM formation and pH, Pearson method showed r = 0.4658 for SWTP and r = 0.3232 for RWDS. In the case of residual chlorine, Pearson method showed a relationship of r = 0.7354 for SWTP and r = 0.5623 for RWDS. Results proved a direct relation between THM S concentration and distance of chlorina- tion injection points. The results showed that in SWTP, 42.7 percent of THM compounds were removed after sedimentation and filtration.

Postharvest management of gray mold and brown rot on surfaces of peaches and grapes using electrolyzed oxidizing water

This study evaluated the potential use of near-neutral (pH = 6.3–6.5) electrolyzed oxidizing water (EO water) to inactivate pure cultures of Botrytis cinerea and Monilinia fructicola and to mitigate fungal infection of these organisms on fruit surfaces. Treatment of these organisms, in pure culture, with EO water at concentrations of 25, 50, 75, and 100 ppm total residual chlorine (TRC) and 10 min of contact time resulted in a 6 log 10 spores/mL reduction of both organisms. A dip treatment or a dip and daily spray treatment of EO water were used to evaluate its ability to prevent or delay the onset of surface infection on fruit during postharvest packaging and in retail shelf environments. A 10 minute dip treatment of surface inoculated peaches ( M. fructicola) in EO water prevented infection for 3 days and resulted in a 12.5% incidence of infection and a disease severity rating of 6% after 5 days of storage at 25 °C. Dipping of green table grapes inoculated with B. cinerea into EO water prevented infection for 7 days and resulted in a 1% incidence of infection and a disease severity rating of 2% after 10 days of storage at 25 °C. A dip and daily spray of peaches with EO water prevented infection for 12 days and resulted in a 10% incidence of infection and a 6% disease severity after 14 days of storage at 25 °C. A dip and daily spray of grapes with EO water prevented infection for 24 days and resulted in a 2% incidence of infection and a disease severity rating of 2% after 26 days of storage at 25 °C. The results from this study suggest that these solutions may prove to be effective for postharvest sanitation of fruit surfaces prior to packaging and may increase the shelf life of the fruit in commercial settings.

Modeling HAA biodégradation in biofilters and distribution systems

A one‐dimensional plug‐flow reactor equation with pseudo‐first‐order biodegradation kinetics was used to model the fate of haloacetic acids (HAAs) in biologically active filters and water distribution systems. Overall, the model calculations suggested that biodegradation was likely to lead to significant HAA removals in biologically active filters but not in most distribution systems. Relatively high total biomass densities (e.g., > 105 cells/cm2) were needed for significant HAA removals (i.e., > 10%) in both systems. Such biomass densities are unlikely in US distribution systems where relatively high total chlorine residuals inhibit the development of biofilm on the pipe walls. Biodegradation of HAAs is possible in distribution systems with intentionally low total chlorine residuals (as in some European systems) or where the residual has been depleted, such as high‐residence‐time locations or dead ends. Biologically active filters can be very efficient at removing HAAs, however, because these filters typically contain relatively high biomass densities.

Avaliação da qualidade físico-química de alimentos comercializados em restaurantes self-service

O consumo de alimentos fora do domicílio vem aumentando no Brasil, podendo expor a riscos sua qualidade e a saúde dos consumidores. Assim, este trabalho avaliou a qualidade físico-química dos alimentos servidos nos balcões de restaurantes self-service no município de Praia Grande/SP, em 2006. Foram coletadas 154amostras de alimentos, compreendendo água, óleo de fritura, salada crua e salada de maionese. As análises realizadas nas amostras de água foram odor, cor aparente, turbidez, pH, fluoreto, cloro residual livre e cloro residual total. Nos óleos foram analisados em laboratório a acidez e os compostos polares e, no momento da coleta, a temperatura e a prova denominada “oil test”. Nas saladas cruas foram realizadas análises microscópicas e, nas de maionese, análises sensoriais e macroscópicas. Os resultados obtidos demonstraram que 52% das amostras de água foram reprovadas, principalmente pelo parâmetro fluoreto; nos óleos foram25% de reprovação; já nas saladas cruas foi de 90% de aprovação e nas saladas de maionese 100% foram aprovadas. Esses resultados demonstram a importância das boas práticas de fabricação e manipulação em unidades de alimentação e que o monitoramento das preparações comercializadas em restaurantes self-service é de fundamental importância para garantir a seguridade do alimento fornecido ao consumidor.

Corrosion of marine carbon steel by electrochemically treated ballast water

Laboratory weight-loss measurements, electrochemical tests and SEM techniques were used to study the corrosive behaviour of electrolysed ballast water on marine carbon steel. Experimental results showed that for the mass concentration of Total Residual Chlorine (TRC) being 7.5mg/l, 17mg/l and 28mg/l respectively, the corrosion rates within seven days were 1.25, 1.46 and 1.7 times those in natural seawater. The corrosion rates decreased as time progressed. The corrosion rate in the electrolysed seawater is controlled by the cathodic process which is mass transfer controlled. The SEM observation showed that the topographies of carbon steel corroded in electrolysed ballast water with mass concentration of TRC 7.5mg/l and 17mg/l were characterised by denudation and rupture. Both the weight-loss and electrochemical tests revealed that the chlorinated seawater accelerated the corrosion rate and that this is consistent with result of the SEM observation

The decontaminative effects of acidic electrolyzed water for Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes on green onions and tomatoes with differing organic demands

Acidic electrolyzed water (AC-EW) has strong bactericidal activity against foodborne pathogens on fresh vegetables. However, the efficacy of AC-EW is influenced by soil or other organic materials present. This study examined the bactericidal activity of AC-EW in the presence of organic matter, in the form of bovine serum against foodborne pathogens on the surfaces of green onions and tomatoes. Green onions and tomatoes were inoculated with a culture cocktail of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes. Treatment of these organisms with AC-EW containing bovine serum concentrations of 5, 10, 15, and 20 ml/l was performed for 15 s, 30 s, 1 min, 3 min and 5 min. The total residual chlorine concentrations of AC-EW decreased proportional to the addition of serum. The bactericidal activity of AC-EW also decreased with increasing bovine serum concentration, whereas unamended AC-EW treatment reduced levels of cells to below the detection limit (0.7 logCFU/g) within 3 min.

Dynamic control of disinfection for wastewater reuse applying ORP/pH monitoring and artificial neural networks

This study applies on-line pH and oxidation-reduction potential (ORP) monitoring and artificial neural network models to dynamically control the wastewater chlorination and dechlorination dosage for reuse purposes. A series of wastewater chlorination and dechlorination experiments were conducted in a continuous laboratory-scale reactor. The ORP and pH variations in raw wastewater, and chlorination and dechlorination reactors were monitored on-line. Artificial neural networks (ANNs) were used to build control models using the monitored ORP and pH data. Another series of continuous experiments were conducted to evaluate the proposed control strategy for meeting different requirements for total coliform counts and residual chlorine concentrations for different wastewater reclamation purposes. The dynamical controlled experimental results show that chlorination and dechlorination were effectively controlled, and that appropriate disinfection efficiencies were achieved and remaining chlorine residuals in effluent were controlled simultaneously for different treatment targets. This ANN control method is simple and has potential benefits in reducing chemical costs for wastewater chlorination and dechlorination.

Reduction of trihalomethane formation and detoxification of microcystins in tap water by ozonation

The efficiency of ozonation in comparison to chlorination for removal of microcystins and production of trihalomethanes (THMs) in water was investigated. One hundred and ninety water samples of ozone and chlorine treated water were collected at a water treatment plant between August 2004 and March 2005. The level of THMs, total organic carbon and residual chlorine were determined. Protein phosphatase 2A inhibition assay was used to detect microcystins and the presence of microcystins was confirmed by HPLC. The results show that 91.5% of the THM species in treated water was chloroform and 8.5% was bromodichloromethane. The mean THM level± standard error of mean in chlorinated water (CW) (45.1±3.0 μg/L) was higher than the mean of THM level in ozonated water (OW) (18.6±2.2 μg/L). In addition, no OW sample exceeded the first stage U.S. EPA maximum THM contaminant level for drinking water (80 μg/L) and only 8% of these samples exceeded the second stage level (40 μg/L). On the other hand, 3% of CW samples exceeded 80 μg/L and 68% exceeded the 40 μg/L level. The microcystin level in all water samples was below the WHO guideline value (1 μg/L) for drinking water.

Reduction of bacteria on spinach, lettuce, and surfaces in food service areas using neutral electrolyzed oxidizing water

Food safety issues and increases in food borne illnesses have promulgated the development of new sanitation methods to eliminate pathogenic organisms on foods and surfaces in food service areas. Electrolyzed oxidizing water (EO water) shows promise as an environmentally friendly broad spectrum microbial decontamination agent. EO water is generated by the passage of a dilute salt solution (∼1% NaCl) through an electrochemical cell. This electrolytic process converts chloride ions and water molecules into chlorine oxidants (Cl 2, HOCl/ClO −). At a near-neutral pH (pH 6.3–6.5), the predominant chemical species is the highly biocidal hypochlorous acid species (HOCl) with the oxidation reduction potential (ORP) of the solution ranging from 800 to 900 mV. The biocidal activity of near-neutral EO water was evaluated at 25 °C using pure cultures of Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Listeria monocytogenes, and Enterococcus faecalis. Treatment of these organisms, in pure culture, with EO water at concentrations of 20, 50, 100, and 120 ppm total residual chlorine (TRC) and 10 min of contact time resulted in 100% inactivation of all five organisms (reduction of 6.1–6.7 log 10 CFU/mL). Spray treatment of surfaces in food service areas with EO water containing 278–310 ppm TRC (pH 6.38) resulted in a 79–100% reduction of microbial growth. Dip (10 min) treatment of spinach at 100 and 120 ppm TRC resulted in a 4.0–5.0 log 10 CFU/mL reduction of bacterial counts for all organisms tested. Dipping (10 min) of lettuce at 100 and 120 ppm TRC reduced bacterial counts of E. coli by 0.24–0.25 log 10 CFU/mL and reduced all other organisms by 2.43–3.81 log 10 CFU/mL.

Qualitative monitoring of tertiary treated wastewater reuse extensive distribution system: total coliforms number and residual chlorine concentration

During a 5-month summer period, samples of tertiary treated wastewater flowing in an extensive distribution system composed of storage tanks and pipes were collected at 2-week intervals, from 21 different sampling points, including the exit from the wastewater treatment plant (WWTP). The WWTP producing this effluent treated one of the most popular European tourist resorts on the north coast of the island of Crete, at the southernmost point of Greece. The average summer equivalent population treated by the plant exceeded 50,000, falling to under 5,000 in the winter. The samples were analyzed for total coliforms number (TC in cfu / 100 mL) and residual chlorine concentration (RCHL in mg/L). In almost 60% of the samples the TC number was so large that it could be safe to suggest that the WWTP and distribution system failed to reach the EPA standards for wastewater reuse for tree irrigation (faecal coliforms ≤ 200 cfu/100 mL and RCHL < 1 mg/L) due mainly to inflow and septage handling, above designed limits. The licensing operational and reuse standards were set in TC ≤ 500 cfu/100 mL, where 76% of the analyzed samples recorded larger values. It was also estimated that in 14% of the samples the wastewater quality failed to reach even the less strict WHO standards of FC ≤ 1.000 cfu/100 mL. When chlorination was properly adjusted the effluent quality was improved (last three sets of samplings for each collection point), helped by the WWTP inflow decrease. As a result the values recorded in all tanks and collectors were also improved. However, even then, the required licensing standards were randomly and barely achieved. This suggests that specific wastewater quality standard at the exit of a WWTP do not guarantee that the wastewater will still retain these characteristics at its final application point.

Relationship of nutrient and residual chlorine concentration in treated wastewater with periphytic algae grown in a stream receiving treated wastewater

The ratio of the amount of treated wastewater to river water is increasing in urban areas due to the spread of sewage systems. Treated wastewater is also sometimes extensively used to create streams and other water environments in urban areas. Rivers, streams and other water environments provide valuable habitats for all kinds of aquatic species, but the relationship between such aquatic species and the quality of treated wastewater they inhabit is not clearly understood. This study was carried out to clarify the effect of the water quality of treated wastewater such as nutrients and residual chlorine on periphytic algae grown in a stream receiving treated wastewater using laboratory-scale experimental channels. The following results were obtained. (1) When the range of phosphate (PO4-P) concentration was 0.04 to 0.09 mg/L, the higher the PO4-P concentration, the higher the biomass of periphytic algae and the more dominant the Chlorophyceae. (2) When the range of total residual chlorine (TRC) concentration was 0.07 to 5.8 mg/L, the higher the TRC concentration, the lower the biomass of periphytic algae. When the range of TRC concentration was 0.93 to 5.8 mg/L, this tendency was more pronounced.

RISK ASSESSMENT OF WATER QUALITY IN THREE NORTH CAROLINA, USA, STREAMS SUPPORTING FEDERALLY ENDANGERED FRESHWATER MUSSELS (UNIONIDAE)

Water quality data were collected from three drainages supporting the endangered Carolina heelsplitter (Lasmigona decorata) and dwarf wedgemussel (Alasmidonta heterodon) to determine the potential for impaired water quality to limit the recovery of these freshwater mussels in North Carolina, USA. Total recoverable copper, total residual chlorine, and total ammonia nitrogen were measured every two months for approximately a year at sites bracketing wastewater sources and mussel habitat. These data and state monitoring datasets were compared with ecological screening values, including estimates of chemical concentrations likely to be protective of mussels, and federal ambient water quality criteria to assess site risks following a hazard quotient approach. In one drainage, the site-specific ammonia ecological screening value for acute exposures was exceeded in 6% of the samples, and 15% of samples exceeded the chronic ecological screening value; however, ammonia concentrations were generally below levels of concern in other drainages. In all drainages, copper concentrations were higher than ecological screening values most frequently (exceeding the ecological screening values for acute exposures in 65-94% of the samples). Chlorine concentrations exceeding the acute water quality criterion were observed in 14 and 35% of samples in two of three drainages. The ecological screening values were exceeded most frequently in Goose Creek and the Upper Tar River drainages; concentrations rarely exceeded ecological screening values in the Swift Creek drainage except for copper. The site-specific risk assessment approach provides valuable information (including site-specific risk estimates and ecological screening values for protection) that can be applied through regulatory and nonregulatory means to improve water quality for mussels where risks are indicated and pollutant threats persist.