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Potential Effects of Chemical Methods on Listed Species and Critical Habitats Associated with CRB Water Bodies

The following table compiles information for each listed species and associated designated critical habitat(s) known to occur in the CRB. The table briefly summarizes key species life history attributes and vulnerabilities, the potential effects of an action on key life stages and critical habitats, and species-specific BMPs that can reduce detrimental effects. If no documented vulnerabilities are listed, it is unknown what, if any, impacts may occur to any life stages and critical habitats. 


Potential estimated effects of chemical treatments on important life history needs and critical habitat ( for listed species whose life history needs are partially, or entirely, met by CRB water bodies. This table also includes species-specific best management practices to avoid or lessen impacts from chemical treatment activities. The chemical methods considered below do not reflect the entirety of chemical method options, but are limited in scope to include the chemical methods most likely to be used in an open-water dreissenid rapid response scenario within the CRB.


Toxicity of potash to ungulates: There is no published information on the effects of potash on any life stage of ungulates, or this particular ungulate species.

Toxicity of EarthTec QZTM to ungulates: There is no published information on the effects of EarthTec QZTM on ungulates, however, sheep can be particularly sensitive to products containing copper sulfate, possible due to inefficient copper excretion (Oruc et al. 2009). The toxic doses of copper sulfate for cattle are 200–880 mg/kg. Sheep are ten times more sensitive; they have a toxic dose of 20–110 mg/kg of copper sulfate (Thompson 2007).

Toxicity of Zequanox® to ungulates: There is no published information on the effects of Zequanox® on any life stage of ungulates, or this particular ungulate species.



Toxicity of potash to birds: There is no published information on the potential negative effects of potash on least terns, piping plovers, red knots, western snowy plovers, yellow-billed cuckoos, or other avian species. Potassium chloride (KCl) is used as a supplement (0.2 and 0.4% KCl) in diet or drinking water of poultry to reduce the effects of high environmental temperature by maintaining the water/electrolyte balance (Dai et al. 2009).

Toxicity of EarthTec QZTM to birds: Limited information is available on the toxicity of copper sulfate to wild birds (Eisler 1998). A flock of captive 3-week-old Canada geese (Branta canadensis) used a pond treated with copper sulfate; Ten of the geese died nine hours after ingestion of roughly 600 mg/kg copper sulfate (Henderson and Winterfield 1995). Although copper is known to be moderately toxic to birds (Boone et al. 2012), copper sulfate poses less of a threat to birds than to other animals - The lowest lethal dose (LDLo) for this material in pigeons and ducks is 1,000 mg/kg and 600 mg/kg, respectively (TOXNET 1975-1986). The oral LD50 for Bordeaux mixture in young mallards is 2,000 mg/kg (Tucker and Crabtree 1970). The toxicity of copper to aquatic life depends on its bioavailability, which is strongly dependent on pH, the presence of dissolved organic carbon (DOC), and water chemistry, such as the presence of calcium ions (

Toxicity of Zequanox® to birds: Zequanox has a “practically non-toxic” designation for birds. No mortality was observed after feeding mallards a 2,000 mg/kg dose of live P. fluorescens strain CL145A (Bureau of Reclamation 2011). The no observable effect limit (NOEL) was set at >2,000 mg/kg and classified Zequanox® as “practically non-toxic to mallard.”



Toxicity of potash to amphibians: Pollution is the 2nd major threat to amphibian populations (IUCN 2008). Agricultural chemicals are a potential cause of amphibian declines (Relyea and Mills 2001), and malformed amphibians have been reported to occur in agricultural areas where pesticides and fertilizers are applied extensively (Ouellet et al. 1997, Taylor et al. 2005). Agricultural pesticides can affect amphibian growth, development, reproduction, and behavior (Carey and Bryant 1995). There is no published information on the potential negative effects of potash on amphibian populations, however, introduction of potash into a water body would alter the water chemistry, and in shallow portions sectioned off with barriers, would raise the water temperature, albeit temporarily (note: Potash itself would not alter the water temperature, but barricading a portion of the water body could increase the water temperature in the barricaded portion because of lack of mixing with deeper, colder water in the water body).

Toxicity of EarthTec QZTM to amphibians: Larval ambystomatids were highly sensitive to Cu with 50% mortality at 18.7, 35.3, and 47.9 ppb for three species. Cu also caused reduced growth rates in A. talpoideium (Savannah River Ecological Laboratory 2016).

Concentrations of copper sulfate were found to be toxic to amphibians at or below those recommended for plant control – 0.31 mg/L was lethal to northern leopard frog tadpoles (Landé and Guttman 1973); Fort and Stover (1997) documented susceptibility to copper with increased age in African clawed frogs (Xenopus laevis) - LC50 values of 1.32 mg/L for embryos, and 0.20 mg/L for 12-16 day-old tadpoles. Growth of African clawed frogs was reduced at concentrations as low as 0.048 mg/L, and completely inhibited at 1.3 mg/L in embryos (Fort and Stover 1997). Distal hind limb aplasia, which is a sensitive indicator of copper toxicosis, occurred in 8.5% of larvae exposed to 0.05 mg/L copper (Fort and Stover 1997).

Toxicity of Zequanox® to amphibians: There is no published information on the toxicity of Zequanox® to amphibians at any key life stage.



Generally, younger fish in juvenile and fry stages are considered for more susceptible to most aquatic toxicants than adult fish (Weber 1993); in addition, there are species-specific differences in sensitivities to toxicants (Lazorchak 2007).

Toxicity of potash (KCl) to fish: The efficacy of potassium chloride treatment is inhibited in the presence of elevated dissolved solids, in particular the concentration of sodium (Moffitt et al. 2016, Stockton-Fiti and Moffitt 2017).

Based upon the acute toxicity testing of KCl using both juvenile Brook Trout (Salvelinus fontinalis) and juvenile Chinook Salmon (Oncorhynchus tshawytscha), acute lethal effects of potash on these salmonids at these life stages are not expected at concentrations commonly used to control invasive dreissenid mussels (100 mg/L) (Densmore et al. 2018). Exposure concentrations of as much as 800 mg/L KCl, eight times greater than the dose of KCl used as a molluscicide, were applied to these fish species in static systems for 96 hours; there was no evidence of mortality attributable to KCl exposure among either species (Densmore et al. 2018). Behavioral or gross morphological effects on these fish from KCl-based molluscicide applications at levels up to 800 mg/L were also not indicated (Densmore et al. 2018). Hillard et al. (2019) exposed  Fall Chinook Salmon eggs within 24 hours of fertilization to 750 mg/L potassium chloride for one hour followed by 20 mg/L formalin for three hours to disinfect the eggs and kill any zebra mussel larvae. There was no effect on salmon egg viability.

Several listed fish species forage on invertebrates, particularly during juvenile life stages. The ecotoxicity of muriate of potash on invertebrates is 48 hours @ EC50 @ 337–825 mg/L (Daphnia magna), and 96 hours @ LC50 @ 940 mg Physa heterostropha (Mosaic 2004). Fathead minnow (Pimephales promelas) trials - LC50 @ 880 mg/L KCl for 96 hours (Mount et al. 2007). Daphniid exposure trials – LC50 @ 196 mg/L for 48 hours; significant mortality of sensitive aquatic invertebrates is not expected at the KCl concentrations used to control dreissenids (Densmore et al. 2018). Crayfish (Cambarus spp.) exposure trials resulted in mortality and temporary paralysis at concentrations of 800 and 1,600 mg/L for at least 24 hours (Densmore et al. 2018). Other ecotoxicology studies: Bluegill sunfish (Lepomis macrochirus) – LC50 – 2010 mg/L (Mosaic 2014). Substantial differences exist in the accuracy of models to predict organism survival to introduced toxins, such as potassium, calcium, and magnesium (Pillard et al. 2000). Brook Trout are less sensitive to potassium chloride than Rainbow Trout (Oncorhynchus mykiss), and Fathead Minnows are two to three times more sensitive to KCl than Brook Trout or Rainbow Trout (Lazorchak 2007).

Potash solutions in water can have varied concentrations throughout the water column because of the density of potash relative to the density of water in cold-water conditions (Lund et al. 2017). Hotspots, or accumulations of potash in higher concentrations, can accumulate at deeper depths (Lund et al. 2017).

Toxicity of EarthTec QZTM to fish: Copper is one of the most toxic heavy metals to fish (Nowak and Duda 1996), and is broadly toxic to the salmon olfactory system (Baldwin et al. 2003). According to the label for this product, “this pesticide is toxic to fish and aquatic invertebrates. Waters treated with this product may be hazardous to aquatic organisms. Treatment of aquatic weeds and algae can result in oxygen loss from decomposition of dead algae and weeds. This oxygen loss can cause fish and invertebrate suffocation. Do not use this product in waters with cyprinid and salmonid fish.” EarthTec is produced in the cupric ion form, the most toxic form of copper (Ferguson and Sandoval 2020).

Copper impairs gill gas exchange, upsets salt balance, negatively affects reproductive output and the immune system, affects glucose metabolism and the cellular structure of fish, and negatively affects liver and kidney function (Ferguson and Sandoval 2020).

The proposed low and high application rates are well above the range of salmonids and their prey LC50 (96 hour), and the LC50 (96 hour) for pond snails falls at the lowest proposed application rate (TOXNET 1975–1986). For salmonids, the upper recommended limit is < 0.03 mg/l in hard water (>100 mg/l CaCO3) whereas in soft water, it is <0.0006 mg/l (Ferguson and Sandoval 2020).

Direct bioassay of Rainbow Trout (assumed adult) subject to EarthTec QZTM resulted in a NOEC of 0.240 mg/L copper, and LC50 of 0.294 mg/L copper ( The EPA maximum allowable dose is 1  mg/L. Fish kills have been reported after copper sulfate applications for algae control in ponds and lakes, however, oxygen depletion and dead organisms clogging the gills have been cited as the cause of fish deaths, resulting from massive and sudden plant death and decomposition in the water body (Bartsch 1954, Hanson and Stefan 1984, Masser et al. 2006). Copper can either temporarily, or permanently, disrupt olfaction in fish (Solomon 2009, Ferguson and Sandoval 2020), possibly interfering with their ability to locate food, predators, and spawning streams (Chapman 1978, Jaensson and Olsen 2010).

It is unknown if there are any bioaccumulation effects of EarthTec QZTM; one recent study suggested the fate of copper in the environment is not fully known and should be considered (Lake-Thompson and Hofmann 2019).

Fish eggs are more resistant than young fish fry to the toxic effects of copper sulfate (Gangstad 1986).

  • Juvenile Rainbow Trout were exposed to either hard water, or soft water, spiked with copper for 30 days (Taylor et al. 2000). Fish in the hard-water, high dose (60 µg/L) treatment groups showed an increased sensitivity to copper.

  • The mean 96-hour LC50 (with 95% confidence limits) for copper exposure in alevin, swim-up, parr and smolt Steelhead (Salmo gairdneri) are 28 (27–30), 17 (15–19), 18 (15–22), and 29 (>20) µg/L of copper respectively (Chen and Lin 2001). The mean 96-hour LC50 for copper exposure in alevin, swim-up, parr and smolt Chinook salmon are 26 (24–33), 19 (18–21), 38 (35–44), and 26 (23–35) µg/L of copper respectively. The experiments were done by adding copper as CuCl2.

  • The 48-hour LC50 for Fathead Minnow is 19.2 + 3.1 (mean + SD) mcg/L Cu (Mastin and Rodgers 2000).


Toxicity of Zequanox® to fish: Zequanox requires containment within a barrier system when applied to surface waters for the management of dreissenid mussels; without containment, effective treatment concentrations cannot be maintained (Luoma et al. 2019).

No mortality from Zequanox® has been observed in Fathead Minnows, young-of-the-year Brown Trout (Salmo trutta), and juvenile Bluegill Sunfish (Bureau of Reclamation 2011). Fish trials conducted with dead bacteria have indicated that applications of killed cells were harmless to fish, yet were still highly lethal to Dreissena spp. mussels (Bureau of Reclamation 2011). Temporary, but substantial, reductions in dissolved oxygen were observed in treatment locations during the morning following Zequanox® treatment in two trials, likely due to the presence of the barriers that prevented well-oxygenated water from circulating into treatment zones from adjacent areas in the lake (Whitledge et al. 2015). During one of the few open water treatments using Zequanox®, dissolved oxygen levels declined as a result of using containment barriers (DO values of 0.1ppm were reached within 24 hours, and these hypoxic conditions continued for 7 days) (Lund et al. 2017).

A 2018 study evaluated the effects of Zequanox® on juvenile Lake Sturgeon (Acipenser fulvescens) and Lake Trout (Salvelinus namaycush) (Luoma et al. 2018). No acute mortality was observed in either species; however, significant latent mortality was observed in Lake Trout that were exposed to the highest dose of Zequanox®. Statistically significant, but biologically minimal, differences were observed in the weight (range 20.17 to 21.49 g) of surviving Lake Sturgeon at the termination of the 33 d post-exposure observation period. Survival was not impacted in the Lake Trout in the 100 mg/L treated group for the first 3 weeks; however, impacts were readily detectable 4 weeks (28 d) after Zequanox® exposure. Poor food consumption, emaciation, and abdominal hemorrhaging were observed about 3 to 4 weeks after exposure in some of the Lake Trout exposed to 100 mg/L A.I. of Zequanox®.

Cold water, cool water, and warm water fish were tested for exposure-related effects to Pseudomonas fluorescens, Strain CL145A. (Luoma et al. 2015). Analyses of test animal condition factors and survival revealed that a 24-hour continuous dose of SDP affected all species. Calculated concentrations of SDP that would be lethal to 50 percent of the test animals (LC50) for the cold water species were 19.2 and 104.6 mg/L for Rainbow Trout and Brook Trout, respectively. The LC50 for the cool water species were 185.4, 176.9 and 8.9 mg/L for Yellow Perch (Perca flavescens), Walleye (Sander vitreus), and Lake Sturgeon, respectively. The LC50 for the warm water species were 173.6, 139.4, and 63.1 for the Largemouth Bass (Micropterus salmoides), Smallmouth Bass (Micropterus dolomieu), and Channel Catfish (Ictalurus punctatus), respectively.

Barbour et al. (2021) assessed avoidance behavior of fish to Zequanox® exposure, and determined that Brook Trout, Lake Trout, and Bluegill Sunfish avoided Zequanox®-treated water, and Lake Sturgeon and Fathead Minnow were attracted to Zequanox®-treated water. In the Barbour et al. (2021) study, one species of fish, Yellow Perch, was indifferent to Zequanox®  exposure, likely because of their ability to function in both clear and turbid water and their tolerance to Zequanox® compared to other fishes. Sensitive fish species may avoid Zequanox® treatments, which can reduce overall risk to a species (Barbour et al. 2021).

Crain et al. (2008) assessed the effects of multiple stressors on aquatic environments and concluded effects were additive, or synergistic. Therefore, any of the treatments described above are assumed to adversely affect aquatic species to some degree and for some duration.

Zequanox® greatly increases turbidity (Barbour et al. 2021). Turbidity was 13x higher than in control plots, but there was no difference between treatment and control plots after 8 hours (Luoma et al. 2019). Fish behavioral response to turbidity varies with species and life stage, but has been associated with mortality (Kemp et al. 2011). Although salmonids have the ability to cope with some levels of turbidity during certain life stages (Gregory and Northcote 1993), salmonid populations not normally exposed to high levels of natural turbidity, or anthropogenic sources, may be negatively affected by low levels, e.g., 18-70 NTU (Gregory 1992). Effects of turbidity on salmonids include physiological effects (e.g., gill trauma, osmoregulation challenges, blood chemistry changes, and effects on reproduction and growth), behavioral effects (e.g., avoidance, territoriality, foraging and predation, and homing and migration), and habitat effects (e.g., reduction in spawning habitat, effect on hyporheic upwelling, reduction in BI habitat, and damage to redds (Bash et al. 2001).

Spawning, foraging, and seasonal migrations should be considered when planning Zequanox® treatments (Barbour et al. 2021); altering treatment timing and limiting the treatment area to provide access to refugia may be helpful mitigation steps.


The next portion of the table includes salmon and Steelhead species. Primary constituent elements within critical habitat boundaries are essential for the conservation of these DPSs – these are sites and habitat components that support one or more life stages, and include:


(1) Freshwater spawning sites with water quantity and quality conditions and substrate supporting spawning, incubation and larval development;

(2) Freshwater rearing sites with:

(i) Water quantity and floodplain connectivity to form and maintain physical habitat conditions and support juvenile growth and mobility;

(ii) Water quality and forage supporting juvenile development; and

(iii) Natural cover such as shade, submerged and overhanging large wood, log jams and beaver dams, aquatic vegetation, large rocks and boulders, side channels, and undercut banks.

(3) Freshwater migration corridors free of obstruction and excessive predation with water quantity and quality conditions and natural cover such as submerged and overhanging large wood, aquatic vegetation, large rocks and boulders, side channels, and undercut banks supporting juvenile and adult mobility and survival;

(4) Estuarine areas free of obstruction and excessive predation with:

(i) Water quality, water quantity, and salinity conditions supporting juvenile and adult physiological transitions between fresh- and saltwater;

(ii) Natural cover such as submerged and overhanging large wood, aquatic vegetation, large rocks and boulders, side channels; and

(iii) Juvenile and adult forage, including aquatic invertebrates and fishes, supporting growth and maturation.

(5) Nearshore marine areas free of obstruction and excessive predation with:

(i) Water quality and quantity conditions and forage, including aquatic invertebrates and fishes, supporting growth and maturation; and

(ii) Natural cover such as submerged and overhanging large wood, aquatic vegetation, large rocks and boulders, and side channels.

(6) Offshore marine areas with water quality conditions and forage, including aquatic invertebrates and fishes, supporting growth and maturation.

(d) Exclusion of Indian lands. Critical habitat does not include habitat areas on Indian lands. The Indian lands specifically excluded from critical habitat are those defined in the Secretarial Order, including:

(1) Lands held in trust by the United States for the benefit of any Indian tribe;

(2) Land held in trust by the United States for any Indian Tribe or individual subject to restrictions by the United States against alienation;

(3) Fee lands, either within or outside the reservation boundaries, owned by the tribal government; and

(4) Fee lands within the reservation boundaries owned by individual Indians.

(e) Land owned or controlled by the Department of Defense. Critical habitat does not include any areas subject to an approved Integrated Natural Resource Management Plan or associated with Department of Defense easements or right-of-ways. In areas within Navy security zones identified at 33 CFR 334 that are outside the areas described above, critical habitat is only designated within a narrow nearshore zone from the line of extreme high tide down to the line of mean lower low water.

(f) Land covered by an approved Habitat Conservation Plan. Critical habitat does not include any areas subject to an approved incidental take permit issued by NMFS under section 10(a)(1)(B) of the ESA. The specific sites addressed include those associated with the following Habitat Conservation Plans:

(1) Washington Department of Natural Resources—West of Cascades

(2) Washington State Forest Practices, except those lands on the Kitsap Peninsula overlapping with areas occupied by Puget Sound steelhead and not classified as being in an approved or renewed status by the Washington Department of Natural Resources as of September 2015.

(3) Green Diamond Company.

(4) West Fork Timber Company.

(5) City of Kent.

(6) J.L. Storedahl and Sons.

Specific critical habitat designations for each species can be found in Appendix E.

Aquatic invertebrates

Aquatic invertebrates

Toxicity of potash to mollusks: Freshwater mollusks are particularly sensitive to environmental change, which has made them the most threatened fauna in North America (Johnson et al. 2013, Williams et al. 2008). Naturally high potassium concentrations decreased the diversity of mussel populations in the Missouri River Basin (Imlay 1973). Any river or stream with a potassium concentration of equal to or greater than 7 mg/L lacked mussels whereas mussels could be found in rivers with concentrations of less than 4 mg/L (Imlay 1973). Toxicity studies using two bivalves (Alabama Rainbow (Villosa nebulosa) and Orangenacre Mucket (Hamiota perovalis)), and two gastropods (Round Rocksnail (Leptoxis ampla), and Pebblesnail (Somatogyrus spp.)) concluded that native mussels may be more sensitive to potassium than zebra mussels (48-h LC50 value for 24,000μg/L for juvenile Southern Rainbow (Villosa vibex) mussels—the authors suggested potassium should not be used as a molluscicide (Gibson et al. 2018). Alabama Rainbow had an EC50 value of 15,966 μg/L (95% CI = 12,450–20,476μg/L), whereas Orangenacre Mucket had an EC50 value of 11,938μg/L (95% CI = 10,089–14,134 μg/L). An EC50 value could not be calculated for Round Rocksnail, however it is expected to be much more sensitive than most other species tested (Gibson et al. 2018). At 100μg/L, 50% of the test organisms were classified as dead at the end of the trial but only a third of the test organisms died at the highest concentration (1000μg/L), thus the EC50 value for Round Rocksnail was more than 1000 μg/L. Partial kills (≤33%) were observed at all five concentrations. The pebblesnails had an EC50 value of 7285 μg/L (95% CI = 5739–9245μg/L), which is lower than either mussel species tested in the study (Gibson et al. 2018).

Significant mortality among sensitive aquatic invertebrates, such as daphniids, is not unexpected (Densmore et al. 2018). Other invertebrates, such as crayfish, demonstrate some degree of sensitivity to KCl (Densmore et al. 2018). Crayfish exposed to KCl at higher concentrations (e.g., 800 mg/L–1,600 mg/L) for at least 24 hours experienced immobilization, but half were able to fully recover in fresh water within 24 hours (Densmore et al. 2018).

Toxicity of EarthTec QZTM to invertebrates and mollusks: EarthTec QZTM is toxic to invertebrates. The 48-hour LC50 for the non-biting midge (Chironomus tentans) is 1,136.5 ± 138.6 (mean ± SD) µg/L Cu (Mastin and Rodgers 2000). Reported 48-hour LC50 concentrations for Daphnia magna include 0.00115 mmol CuSO4/L85 and 18.9 ± 2.3 (mean ± SD) µg/L Cu (Mastin and Rodgers 2000). The LC50 for Daphnia pulex was relatively constant at 24, 48, and 72 hours. Reported values were 21–31 µg/L, 20–31 µg/L, and 20–29 µg/L, respectively (Ingersoll and Winner 1982). The 24- and 48-hour EC50(with 95% confidence intervals) for Daphnia similis was 0.035 (0.030–0.042) and 0.032 (0.026–0.039) mg/L Cu, respectively (de Oliveira-Filho et al. 2004).

Copper disrupts surface epithelia function and peroxidase enzymes in mollusks (USEPA 2009). Aquatic snails (Biomphalaria glabrata) had a 24-hour and 48-hour LC50 (with 95% confidence intervals) of 1.868 (1.196–3.068) and 0.477 (0.297–0.706) mg/L Cu, respectively (de Oliveira-Filho et al. 2004). 1-day-old freshwater snail eggs (Lymnaea luteda) were exposed to copper at concentrations from 1 to 320 µg/L of copper for 14 days at 21 °C in a semi-static embryo toxicity test (Khangarot and Das 2010). Embryos exposed to copper at 100 to 320 µg/L died within 168 hours. At lower doses from 3.2–10 µg/L, significant delays in hatching and increased mortality were noted.

Toxicity of Zequanox® to mollusks/mussels/invertebrates: Exposure to Zequanox® caused no mortality to blue mussels (Mytilus edulis) or any of six native North American unionid clam species (Pyganodon grandis, Lasmigona compressa, Strophitus undulatus, Lampsilis radiata, Pyganodon cataracta, and Elliptio complanata) (Bureau of Reclamation 2011). Exposure of duck mussel (Anodonta spp.), non-biting midge (Chironomus plumosus), and white-clawed crayfish (Austropotamobius pallipes) to Zequanox® in a 72-hour static renewal toxicity test at concentrations of 100–750mg active ingredient/liter resulted in LC50 values for Anodonta: >500mg active ingredient/liter, C. plumosus: 1075mg active ingredient/liter, and A. pallipes: >750mg active ingredient/liter, demonstrating that Zequanox® does not negatively affect these species at concentrations required for greater than 80% zebra mussel mortality (i.e., 150mg active ingredient/liter) (Meehan et al. 2014).

Nicholson (2018) conducted a replicated aquatic mesocosm experiment using open-water applications of Zequanox® (100 mg/L of the active ingredient) to determine the responses of primary producers, zooplankton, and macroinvertebrates to Zequanox® exposure in a complex aquatic environment. Short-term increases occurred in phytoplankton and periphyton biomass (250–350% of controls), abundance of large cladoceran grazers (700% of controls), and insect emergence (490% of controls). Large declines initially occurred among small cladoceran zooplankton (88–94% reductions in Chydorus sphaericus, Ceriodaphnia lacustris, and Scapheloberis mucronata), but abundances generally rebounded within three weeks. Declines also occurred in amphipods Hyalella azteca (mean abundance 77% less than controls) and gastropods Viviparus georgianus (survival 73 ±16%), which did not recover during the experiment. Short-term impacts to water quality included a decrease in dissolved oxygen (minimum 1.2 mg/L), despite aeration of the mesocosms.


Toxicity of potash to plants: Potassium plays a critical role in plant growth and metabolism, and contributes to the survival of plants under abiotic or biotic stress (Wang et al. 2013). Potassium can often be deficient in the environment (Truong 2017). At the concentrations used to kill dreissenids, potash would not negatively affect these plant species because of the demonstrated role that potassium plays in plant growth and metabolism (Wang et al. 2013).

Toxicity of EarthTec QZTM to plants: One of the limiting factors in the use of copper compounds is their serious potential for phytotoxicity, or poisonous activity in plants (USEPA 1986). Copper sulfate can kill plants by disrupting photosynthesis. 200 ppm of copper was found in grass five months after it was sprayed with copper sulfate to control liver fluke (TOXNET 1975–1986). Blue-green algae in some copper sulfate-treated Minnesota lakes appeared to become increasingly resistant to the algaecide after 26 years of use (Pimental 1971).

Toxicity of Zequanox®  to plants: Phytotoxicity (degree of toxic effects to plants) of microbial suspensions of Zequanox® were tested on some of the most common aquatic and non-aquatic weed species, including common water plantain (Alisma plantago-aquatica), small-flower umbrella sedge (Cyperus difformis), nightshade, bindweed, mallow, and curly dock (Rumex crispis; MBI 2009). Suspensions at 100 and 200 mg/L were prepared in distilled water and sprayed on the plant species. No phytotoxic symptoms were observed at either test concentration in any of the tested plants.

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