Behavioral and reproductive effects of the lampricides TFM and TFM:1% Niclosamide on native freshwater mussels

The lampricides TFM (3-trifluoromethyl-4′-nitrophenol) and Niclosamide (NIC, 2′, 5-dichloro-4′-nitrosalicylanilide) are used to control sea lamprey populations in the Great Lakes and associated tributaries. Niclosamide is often used as an additive to TFM to reduce the amount of TFM required to control sea lamprey. Concern is growing over the risk that lampricide treatments pose to native freshwater mussels residing in streams. Our objectives were to determine the acute toxicity of TFM and TFM:NIC to free glochidia (removed from the marsupial gills), compare the relative toxicity of TFM and TFM:NIC between free glochidia and brooded glochidia (within the marsupial gills), determine if glochidia age influences toxicity, and assess if exposure of gravid mussels to TFM and TFM:NIC alters behavior and reproduction. Three acute toxicity tests (2:TFM, 1:TFM : NIC) were conducted with glochidia and adults of the plain pocketbook mussel (Lampsilis cardium). In tests with glochidia, viability did not differ across TFM and TFM : NIC concentrations that encompassed typical stream treatments. Glochidia age influenced toxicity as glochidia obtained later in the brooding season were less viable than glochidia obtained earlier in the brooding season. Exposure of adults to elevated concentrations of lampricides often resulted in behavioral effects, but rarely affected reproductive endpoints. Because mussels are long-lived (30 to 100 y), even intermittent and short duration exposures may cumulatively affect mussels over their lifetime. The risks posed by lampricide treatments in the Great Lakes would be further informed by research on the sublethal effects of lampricides, particularly effects on non-target organisms such as mussels.     

Acute toxicity of the lampricides TFM and niclosamide: Effects on a vascular plant and a chironomid species

The lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide have been used for about 60 years to control sea lamprey (Petromyzon marinus) in the Great Lakes Basin and Lake Champlain. To register these chemicals as pesticides in North America, their environmental effects must be reviewed on a periodic basis. As a part of this effort, toxicity of TFM and niclosamide to duckweed (Lemna gibba), and of niclosamide to aquatic midge (Chironomus dilutus), was assessed. Results of these studies indicate that for both lampricides, the no observed and lowest observed effect concentrations (NOEC and LOEC) exceed expected environmental concentrations, with effects only in the highest concentrations tested and the longest exposure times. Duckweed exposed to TFM indicated 7-day LOECs ≥4.88 mg/L for mean specific growth rate and yield, with the half maximal effective concentration (EC₅₀) > 9.74 mg/L. For duckweed exposed to niclosamide, 7-day LOECs for mean specific growth rate and yield ranged from 0.271 to 0.569 mg/L, with the half maximal inhibitory concentration (IC₅₀) 0.725 mg/L or greater depending on the parameter measured. For midge larvae exposed to niclosamide-dosed sediment, the LOEC values based on survival and growth were 26.2 mg/kg and >82.1 mg/kg, respectively, and the EC₅₀ based on survival was 49.6 mg/kg. Based on these data, deleterious effects on aquatic plants and benthic invertebrates are unlikely to result from use of TFM and niclosamide for lamprey control, given that the effect concentrations are in excess of the expected environmental concentrations.     

Contaminant Analysis of Fillets from Great Lakes Coho Salmon, 1980

Analyses of coho salmon from each of the Great Lakes by a single laboratory produced residue data on the accumulation of environmental contaminants which have been banned, severely restricted, or are currently permitted in the basin. Coho salmon from Lake Superior contained only trace amounts or low levels of most toxic substances quantified; Lake Erie fish were contaminated with low levels of a number of pesticides and industrial compounds; relatively higher residues were detected in coho from Lake Huron and Lake Michigan; and the highest concentrations for a number of compounds were found in fillets from coho from Lake Ontario. Contaminant concentrations in migratory coho salmon indicate open lake contaminant problems rather than point source or nearshore conditions. Tissue residues were less than USFDA action levels, used by many agencies in assessing the severity of fish contaminant problems. Only mirex concentrations in fish collected from Lake Ontario exceeded a USFDA action level. The data reported in this study generally agree with recent findings from individual state contaminant monitoring programs. Problems with varying analytical and sampling techniques preclude direct comparisons with previously published data of other studies.     

Biological consequences of agricultural and urban land-use along the Maumee River,a major tributary to the Laurentian Great Lakes watershed

Many riverine systems are impacted by a combination of agricultural and urban land use. In this study, we assessed the impacts of high intensity agriculture and urban land use in the Maumee River, the largest Great Lakes tributary, using sunfish (Lepomis spp.). The land use gradient from agricultural headwaters to densely urban areas was hypothesized to be paralleled by a shift in the chemical signature and biological effects. We caged hatchery-reared sunfish at field sites and collected concurrently resident sunfish. We analyzed fish for alterations in morphological indices, hematological characteristics, and anatomical development. Water, sediment, and fish tissues were analyzed for pesticides, pharmaceuticals, and personal care products. Chemicals were detected in all samples, and no clear agricultural/urban distinction in water chemistry was apparent. We detected forty-three chemicals (19% of analyzed) in at least half of the water samples, and 101 chemicals (44%) in at least one water sample. The pesticides desethylatrazine (100% of samples) and heptachlor epoxide (89%), and pharmaceuticals iopamidol (100%) and sulfamethoxazole (89%) were frequently detected. Resident sunfish were more sensitive than caged sunfish, and both experienced elevated stress responses at urban sites. Declining biological indices suggest contaminant-related impairments which may have altered resource allocation and could have contributed to decreased sexual maturity. Agricultural, and especially urban, contaminants entering aquatic ecosystems as non-point sources affect sunfish biology through acute and chronic exposure. Natural resource managers are advised to broadly assess stressors prior to investing into stream restoration efforts.     

Ecotoxicity of contaminated sediments,a matter of bioavailability

Marine and freshwater mesocosm-scale experiments with contaminated sediments have shown that there is a direct relationship between the accumulated contaminant levels and the feeding habits of the organisms used. The highest levels of PAHs and PCBs were found in the sediment feeding lugworm Arenicola marina and in Tubifex worms. The levels of contaminants in the suspension feeding mussels Mytilus edulis and the zebra mussels, Dreissena polymorpha, were not influenced by the contaminant content of the sediments, but were related instead to the level of contaminants in the sea water above. Intermediate levels were found in the baltic tellin, Macoma balthica, which is a filter feeder as well as a deposit feeder, depending on the availability of food.These results show that there is no simple relationship between contaminant concentration in the sediments and bioavailability. Higher levels of contaminants do not necessarily lead to higher levels of these contaminants in Arenicola, due to differences in the sediment structure and the ageing of the contamination. On the other hand, toxic effects are related to the internal concentrations of certain chemicals. The internal concentrations observed in Arenicola may provide a good estimation of the true bioavailability of sedimentary contaminants and can also be used as an indicator for potential environmental effects.     

Characterization of sediments from Copenhagen Harbour by use of biotests

The potential environmental hazard of sediment samples from Copenhagen Harbour was investigated by a combination of chemical analyses and biological tests. The chemical analyses comprised determination of the content of heavy metals, polycyclic aromatic hydrocarbons and polychlorinated biphenyls, and the biological tests comprised whole sediment bioassays with the amphipod Corophium volutator, testing of a sediment suspension with the Microtox Solid Phase test, and testing of sediment pore water by the copepod Acartia tonsa and the alga Skeletonema costatum. For all sediment samples, the concentrations of contaminants exceeded the Probable Effect Levels and toxic effects should therefore be expected. However, various degrees of toxicity were determined by the biotests with the Microtox Solid Phase test system being the most sensitive, the amphipod and the copepod being intermediately sensitive, and no toxicity of the pore water was registered to the algae. Moreover, no direct correlation between the content of the contaminants in the sediment samples and the registered toxicity could be established. It is therefore concluded that the combination of biotesting and chemical analysis is a valuable tool for evaluating the environmental risks of sediments.     

Organic Priority Pollutants in Nearshore Fish from 14 Lake Michigan Tributaries and Embayments, 1983

Composite, nearshore, whole fish samples of selected species, collected in fall 1983 from 13 Lake Michigan tributaries and Grand Traverse Bay, were analyzed for a wide range of pesticides and priority pollutants using gas chromatography-mass spectrometry. This study was carried out to identify existing source areas for known and previously unrecognized toxic substances. Our strategy was to analyze those resident fish with the highest likely levels of contaminants. All fish analyzed (eight species from southern Michigan to the upper peninsula) exceeded the 2 mg/kg FDA action levels for PCBs, while 50% of the samples exceeded the DDTr IJC objective of 1 mg/kg. St. Joseph River common carp (Cyprinus carpio) carried the heaviest contaminant burden of all fish examined for PCBs (27.6 mg/kg), DDTr (10.2 kg/mg), and toxaphene (3.3 mg/kg); chlordane levels (0.85 mg/kg) were second highest to those in Kalamazoo River common carp (0.87 mg/kg). Concentrations of PCBs, toxaphene, DDT, DDE, and other pesticides were higher in bottom-feeding fish, such as common carp, than in top predators, e.g., northern pike (Esox lucius). Bottom feeders are relatively fatty fish, and live and feed near contaminated sediments, which increases their potential to bioaccumulate fat-soluble contaminants. Pesticides were also present in elevated concentrations in fish from sites with higher industrial and agricultural development.     

An Introduction to the Niagara River/Lake Ontario Pollution Problem

Considerable public concern about contamination of Lake Ontario has been generated by suspected leakage of toxic chemicals from a multitude of hazardous waste dumps and by the several major chemical outfalls along the United States side of the upstream Niagara River. A cooperative effort by Canadian and United States research scientists has begun to provide the basic information which may be required to enforce controls of loadings of toxic chemicals to this river/lake system. A holistic ecosystem approach, involving analyses of many contaminants in a variety of aquatic media, is necessary to properly manage the problem and assist in setting priorities.     

Organochlorine and Heavy Metal Residues in Standard Fillets of Coho and Chinook Salmon of the Great Lakes - 1980

Coho (Oncorhynchus kisutch) and chinook (O. tshawytscha) salmon were collected from seven Michigan tributaries to the Great Lakes and analyzed for chlorinated hydrocarbon pesticides, polychlorinated biphenyls (PCB), and metals. Analyses of standard skin-on fillets of these salmon revealed the presence of PCBs, DDT, dieldrin, zinc (found in one chinook), and mercury, but no detectable residues of aldrin, chlordane, heptachlor, heptachlor epoxide, toxaphene, arsenic, cadmium, chromium, copper, or lead. Chlorinated hydrocarbon contaminants were present at significantly lower levels than were found in salmon samples collected in 1971. No sample of either species exceeded FDA action levels for DDT, dieldrin, or mercury; however, 6 of 63 coho and 29 of 50 chinook salmon exceeded the FDA action level for PCBs. In general, chinook salmon had higher contaminant levels than did coho salmon collected at the same time and location. Salmon collected from the southernmost Lake Michigan tributary had highest contaminant levels (especially PCBs) while salmon from the Lake Erie tributaries had lowest contaminant levels. Samples analyzed as skinless fillets showed dramatically reduced levels of PCBs and DDT analogs compared to standard, skin-fillets from the same fish. A strong linear correlation was observed between residues of DDT and PCBs in samples analyzed     

Use of comprehensive two-dimensional gas chromatography for the broad screening of hazardous contaminants in urban wastewaters.

The list of priority chemicals included in various regulations such as the European Water Framework Directive, as well as the list of hazardous contaminants identified in the aquatic environment, are increasing at an accelerated pace. Therefore, there is a need for broad spectrum methods capable of simultaneously determining hundreds, if not thousands, of contaminants. For the analysis of non-polar or semi-polar contaminants, comprehensive two-dimensional gas chromatography (GC x GC) is more powerful than conventional gas chromatography thanks to a separation on two different stationary phases. This paper reports the use of GC x GC for a broad screening of hazardous contaminants in an urban wastewater plant. Comparison between the raw and treated wastewater has been carried out using a semi-quantitative approach. A variety of drugs, personal care products, pesticides, carcinogens and compounds toxic for reproduction, were identified. Most of these compounds were removed or decreased by this wastewater treatment plant. Preliminary results from this single plant will need to be confirmed by a more extensive study before drawing conclusions on the removal efficiency of 2D-GC amenable compounds.     

Monitoring metal and persistent organic contaminant trends through time using quagga mussels (Dreissena bugensis) collected from the Niagara River

Historically, the Niagara River received the discharge of persistent bioaccumulative and toxic chemicals from municipal and industrial outfalls and hazardous waste landfills. American and Canadian governments have coordinated investigations of chemicals entering the river and initiated remedial measures and monitoring programs with a goal to reduce loadings of toxic chemicals to the river. This study, a component of the Ontario Ministry of Environment Mussel Biomonitoring Program, compares contaminant concentrations in quagga mussels (Dreissena bugensis) collected from nine locations in the Niagara River in 1995 and 2003 to assess anticipated changes in tissue concentrations of contaminants in response to ongoing remedial efforts by government agencies and local industries. The concentrations of persistent organic compounds (e.g., PCBs, hexachlorobenzene, hexachlorobutadiene, octachlorostyrene) in quagga mussels in 2003 were lower than concentrations measured in 1995, consistent with a decrease in reported mean annual concentrations of these compounds in water. Significant differences in total PCB concentrations in mussels between stations (F = 4.6; P < 0.001) suggested sources of PCBs on the American side of the upper Niagara River. In general, highest concentrations of persistent organic compounds were found downstream of the Occidental Chemical Corporation Buffalo Avenue facility suggesting local sources of these contaminants notwithstanding remedial efforts. In contrast, metal concentrations in quagga mussels in 2003 were similar to concentrations found in 1995 and to values reported in the literature for mussels collected from industrialized areas in the Great Lakes. Overall, our results suggest that remedial efforts to improve water quality in the Niagara River have been successful.     

In situ assessment of lampricide toxicity to age-0 lake sturgeon

The lampricides 3-trifluoromethyl-4-nitrophenol (TFM) and 2′, 5-dichloro-4′-nitrosalicylanilide (niclosamide) are used to control sea lamprey (Petromyzon marinus), an invasive species in the Great Lakes. Age-0 lake sturgeon (Acipenser fulvescens), a species of conservation concern, share similar stream habitats with larval sea lampreys and these streams can be targeted for lampricide applications on a 3- to 5-year cycle. Previous laboratory research found that lake sturgeon smaller than 100 mm could be susceptible to lampricide treatments. We conducted stream-side toxicity (bioassay) and in situ studies in conjunction with 10 lampricide applications in nine Great Lakes tributaries to determine whether sea lamprey treatments could result in in situ age-0 lake sturgeon mortality, and developed a logistic model to help predict lake sturgeon survival during future treatments. In the bioassays the observed concentrations where no lake sturgeon mortality occurred (no observable effect concentration, NOEC) were at or greater than the observed sea lamprey minimum lethal concentration (MLC or LC99) in 7 of 10 tests. We found that the mean in situ survival of age-0 lake sturgeon during 10 lampricide applications was 80%, with a range of 45–100% survival within streams. Modeling indicated that in age-0 lake sturgeon survival was negatively correlated with absolute TFM concentration and stream alkalinity, and positively correlated with stream pH and temperature. Overall survival was higher than expected based on previous research, and we expect that these data will help managers with decisions on the trade-offs between sea lamprey control and the effect on stream-specific populations of age-0 lake sturgeon.     

Development of a pH/Alkalinity Treatment Model for Applications of the Lampricide TFM to Streams Tributary to the Great Lakes

It has long been known that the toxicity of the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) is influenced by chemical and physical properties of water. As the pH, conductivity, and alkalinity of water increase, greater concentrations of TFM are required to kill sea lamprey (Petromyzon marinus) larvae. Consequently, the concentration of TFM required for effective treatment varies among streams. Brown trout (Salmo trutta) and sea lamprey larvae were exposed to a series of TFM concentrations in a continuous-flow diluter for 12 h. Twenty five exposures were conducted at various water alkalinities and pHs that treatment personnel encounter during lampricide treatments. Survival/mortality data were analyzed for lampricide concentrations that produced 50 and 99.9% mortality (LC₅₀ and LC_99.9) for sea lamprey larvae and 25 and 50% mortality (LC₂₅ and LC₅₀) for brown trout. Linear regression analyses were performed for each set of tests for each selected alkalinity by comparing the 12-h post exposure LC_99.9 sea lamprey data and LC₂₅ brown trout data at each pH. Mortality data from on-site toxicity tests conducted by lampricide control personnel were compared to predicted values from the pH/alkalinity prediction model. Of the 31 tests examined, 27 resulted in the LC₁₀₀s (lowest TFM concentration where 100% mortality of sea lamprey was observed after 12 h of exposure) falling within 0.2 mg/L of the predicted sea lamprey minimum lethal (LC_99.9) range. The pH/alkalinity prediction model provides managers with an operational tool that reduces the amount of TFM required for effective treatment while minimizing the impact on non-target organisms.     

Effects of vegetations on the removal of contaminants in aquatic environments： A review

This paper reviews the removal of contaminants including nutrients, metals and organic pollutants by vegetations in aquatic environments. The removal efficiencies are considered with respect to 16, 19 and 14 kinds of different aquatic plants, respectively in three tables. Due to different characteristics, the removal effects of plants on contaminants from the overlying water differ greatly. The vegetation can improve the water quality mainly through two ways： （1） to adsorb and absorb pollutants from water, （2） to prevent pollutants from releasing from sediment. The contaminant removal mechanisms of vegetations and related physical, chemical and biological effects are discussed. The effects of vegetations on the contaminant removal are found to depend on the environmental conditions, the number and the type of plants, the nature and the chemical structure of the pollutants. In addition, the contaminant release and reoaoval by vegetations under hydrodynamic conditions is specially addressed. Further research directions are suggested.     

The Influence of the Niagara River on Contaminant Burdens of Lake Ontario Biota

Top predator and forage fish species, netplankton (> 153 μm), zooplankton, and benthic macroinvertebrates from Lake Erie and Lake Ontario were analyzed for whole body levels of trace metals and organic contaminants. Comparison of contaminant concentrations in similar aquatic food chains from both lakes indicated that levels of PCB, DDT, mirex, and mercury are significantly greater (P <0.05) in the biota of Lake Ontario. The Niagara River, the single largest tributary to Lake Ontario, was confirmed as a major source of organic contaminants and trace metals. Organic contaminants are adsorbed to the particulate load of the river and dispersed throughout Lake Ontario by the circulating currents. There was no significant regional difference (P<0.05) in the degree of contaminant accumulation by the pelagic food chain of Lake Ontario. Conversely, both inorganic and organic contaminant levels in the demersal amphipod, Pontoporeia affinis, were significantly different (P<0.05) between the eastern and western basins of Lake Ontario. The uptake and concentration of contaminants at the sediment-water interface is suggested as a possible mechanism to explain this observed difference.     

Absorption of Hydrophobic Contaminants from Ingested Chlamydomonas rheinhardtii and Chlorella vulgaris by Zebra Mussels,Dreissena polymorpha

The zebra mussel, Dreissena polymorpha, has the potential to influence contaminant cycling in freshwater systems because of its large population density, high lipid content, and high filtering rate. Ingestion of contaminated particles such as algae dominates exposure routes for the zebra mussel for strongly particle-associated contaminants. However, the data on absorption efficiency are limited and models to predict contaminant accumulation for the lower food web have identified the absence of such data as limiting and necessary to improve predictions. Accumulation of 2,2′,4,4′-tetrachlorobiphenyl (TCBP), 3,3′,4,4′,5-pentachlorobiphenyl (PCBP), 2,2′,4,4′,5,5′-hexachlorobiphenyl (HCBP) and 1,1- dichloro-2,2-bis[4-chlorophenyl] ethylene(DDE) was determined at two algal concentrations from exposures to contaminated Chlamydomonas rheinhardtii and Chlorella vulgaris. The contaminant absorption efficiencies were determined based on a chemical-mass-balance model. Mussel absorption efficiencies for the four chemicals at the two different algal concentrations for the two algal species ranged from 68.3% to 95.4% and were independent of algal concentrations and algal species for the same chemical.     

Sea Lamprey Control Techniques: Past,Present, and Future

Early attempts at controlling the sea lamprey (Petromyzon marinus) in the Great Lakes in the 1950s centered on a variety of mechanical and electrical devices to prevent migration of adults into tributary streams to reproduce. Although some of the devices were effective, it became obvious that barriers alone were not an adequate solution to the lamprey predation problem. Researchers screened over 6,000 chemicals before they found 3-trifluoromethyl-4-nitrophenol (TFM), a toxicant to which sea lamprey larvae and adults are particularly sensitive. Bayer 73 enhances lampricidal activity when used in combination with TFM. In 1970, the U.S. Environmental Protection Agency (EPA) required additional studies to support continued use and registration of TFM. Most of these studies have been completed, but the EPA could cancel the existing registration in the event of unforeseen problems or hazards associated with its use. Therefore, the Great Lakes Fishery Commission continues to support research on lamprey control techniques, such as new formulations of TFM and Bayer 73, sterile male techniques, and attractants and repellents. Development of an integrated management program to combat the sea lamprey is being planned. This concept involves the systematic application of multiple techniques in a way that will exert maximum impact on the sea lamprey. Possible programs may involve chemical, biological, and physical control techniques, each of which would be subject to its own registration or regulatory requirements.     

Exploring the potential synergistic effects of chemical disinfectants and UV on the inactivation of free-living bacteria and treatment of biofilms in a pilot-scale system

The main objective of this study is to explore possible synergistic or additive effects of combinations of chemical disinfectants (sodium hypochlorite, peracetic acid, hydrogen peroxide, chlorine dioxide) and UV in their efficacy in inactivating free-living bacteria and removing biofilms. In contrast to most studies, this study examines disinfection of municipal water in a pilot-scale system using a mixed bacterial suspension, which enables a better simulation of the conditions encountered in actual industrial environments. It was shown that the combination of either hypochlorite, hydrogen peroxide, peracetic acid, or chlorine dioxide with UV yielded additive effects on the inactivation of free-living bacteria. Actual synergy was observed for the combination of UV and 5 ppm hydrogen peroxide. Regarding biofilm treatment, additive effects were observed using the combination of hydrogen peroxide and UV. The promising results obtained in this study indicate that the combination of UV and chemical disinfectants can considerably reduce the amount of chemicals required for the effective disinfection and treatment of biofilms.     

Bioassessment of contaminant transport and distribution in aquatic ecosystems by chemical analysis of burrowing mayflies (Hexagenia)

Burrowing mayfly nymphs (Ephemeroptera) inhabit and ingest fine-grained sediments and detritus that may be enriched with metals and persistent organic compounds. The burrowing nymphs can externally adsorb and internally assimilate these contaminants, providing a link for the food chain transfer of potentially toxic substances from sediments to organisms in higher trophic levels. The emergent adults are short-lived and do not feed, thus their gut contents do not contribute greatly to their total contaminant burden. These characteristics make Hexagenia spp. and certain other burrowing mayflies useful for assessing ecosystem contamination. General protocols are presented for the collection, processing and analysis of emergent mayflies to assess the spatial distribution and bioaccumulation of sediment-associated contaminants in aquatic ecosystems. Two essential components of this bioassessment approach are a network of on-site volunteers with the materials and instructions needed to correctly collect and store samples and quality assurance procedures to estimate the accuracy of chemical analyses. The utility of this approach is demonstrated with an example of its application to the Upper Mississippi River (USA). Determination of cadmium, mercury and polychlorinated biphenyl congeners in emergent Hexagenia bilineata from a 1250km reach of this river revealed (1) several source areas of contaminants and (2) distinct patterns in the bioaccumulation (and apparent sediment-associated transport) of each residue on both small and large spatial scales.     

Monitoring toxicity of industrial wastewater and specific chemicals to a green alga, nitrifying bacteria and an aquatic bacterium.

Treatment plants may be exposed to a whole range of toxic organic and inorganic compounds that may inhibit the removal of organic matter and nitrogen. In order to secure maximum treatment efficiency, the plant manager has to monitor the toxicity of the influent sewage. With regard to the receiving water the manager also has to make sure that toxicity in the influent is significantly reduced during treatment. Because a whole range of chemicals may be present, chemical analysis may be insufficient and expensive as a control instrument. Instead, direct toxicity measurements are preferable to capture the complexity of the wastewater. The monitoring methods have to be relevant and sensitive for the processes in the treatment plant, i.e. removal of organic matter and nutrients. The methods also have to be simple and inexpensive. The paper reports on recent results from the application of nitrification, algae and Biotox tests, and summarises the experience with monitoring of toxicity. Although the sensitivity of the tests varies with respect to individual chemicals or group of chemicals, the application of a combination of the tests gives a high likelihood of detecting toxic impacts on treatment plants and receiving waters.