Zinc in freshwater
Toxicant default guideline values for protecting aquatic ecosystems
Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals’ of the ANZECC & ARMCANZ (2000) guidelines.
The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.
Description of chemical
Zinc can enter the environment from both natural processes (e.g. weathering and erosion) and anthropogenic (e.g. zinc production, waste incineration, urban runoff) processes (CCREM 1987). Zinc is an essential trace element required by most organisms for their growth and development. It is found in most natural waters at low concentrations (Table 8.3.2 of the ANZECC & ARMCANZ 2000 guidelines).
Summary of factors affecting zinc toxicity
- Zinc is an essential trace element required by many aquatic organisms.
- Zinc toxicity is hardness–dependent (also alkalinity) and a hardness algorithm is available (Table 3.4.3 of the ANZECC & ARMCANZ 2000 guidelines). Toxicity decreases with increasing hardness and alkalinity (Holcombe & Andrew 1978, Mount 1986).
- Levels of dissolved organic matter found in most freshwaters are generally sufficient to remove zinc toxicity but often not in very soft waters. Speciation measurements can account for this.
- Zinc forms complexes with dissolved organic matter, the stability of which depends on pH. Organic complexation is common in marine waters.
- Zinc is adsorbed by suspended material. Filtration and speciation measurements should account for this. There is conflicting evidence on its bioavailability after adsorption.
- Zinc toxicity generally decreases with decreasing pH, at least below pH 8. Trends are complex above pH 8.
- Zinc uptake and toxicity generally decreases as salinity increases.
In natural waters at pH≤8.5, the predominant species is the +2 valency state (Stumm & Morgan 1996). In estuarine waters, at neutral pH, the predominant species of zinc is Zn2+, whereas at higher pH (pH≥8), in the open sea, the hydrolysed species, ZnOH+ and Zn(OH)2, become the major species (Young et al. 1980, Bervoets et al. 1996).
A variety of techniques are available for determining the speciation of zinc in water. These include:
- Analytical techniques, such as physical separation (e.g. (ultra)filtration, dialysis, centrifugation), polarography, voltammetry (e.g. anodic/cathodic stripping voltammetry), ligand competition and ion exchange (Cheng et al. 1994, Apte & Batley 1995, Vega et al. 1995)
- Theoretical techniques, such as geochemical modelling (Wilson 1978, Bervoets et al. 1996, Stumm & Morgan 1996).
Bioassays are typically used to ascertain metal-organism interactions. These can be coupled with measured and/or predicted speciation calculations to determine the bioavailability of various zinc species. The current analytical practical quantitation limit (PQL) for zinc is 0.2 µg/L in fresh water (NSW EPA 2000).
Factors that affect the toxicity of zinc
It is generally considered that Zn2+ is the form of zinc primarily responsible for eliciting a toxic response in aquatic organisms. Typically, inorganic and organic complexes ameliorate the uptake and toxicity of zinc by reducing the concentration of Zn2+.
A number of studies have established the uptake and toxicity of zinc in aquatic organisms decreases with increasing water hardness (e.g. Mount 1966, Holcombe & Andrew 1978, Bradley & Sprague 1985, Everall et al. 1989). Holcombe and Andrew (1978) determined a zinc toxicity (LC50) in soft water (hardness, 44 mg/L as CaCO3) of 0.76 and 2.4 mg/L to rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis), respectively. In hard water (hardness, 170 mg/L as CaCO3), the corresponding toxicity values were 1.9 mg/L for the rainbow trout and 5.0 mg/L for the brook trout. The difference between the alkalinity (43 mg/L as CaCO3) and pH (7.35) of the two test waters was negligible. The study of Holcombe and Andrew (1978) also indicated that an increase in alkalinity and pH further ameliorated zinc toxicity to the two trout species.
An exponential, inverse relationship has been shown to exist between water hardness and the uptake and toxicity of zinc. An algorithm describing this relationship has been used to calculate a hardness-modified zinc guideline value for protecting aquatic ecosystems in North America (USEPA 1995a,b).
There is a consensus of opinion that below pH 8 zinc toxicity decreases with decreasing pH (Holcombe & Andrew 1978, Bradley & Sprague 1985, Harrison et al. 1986, Everall et al. 1989, Roy & Campbell 1995). At low pH (i.e. pH 4) an increase in toxicity may be observed due to increased acidity (Fromm 1980). Conflicting results have been reported for zinc toxicity at higher pH (8 to 9) (Farmer et al. 1979, Bradley & Sprague 1985, Everall et al. 1989).
Redox will have little direct influence on zinc speciation, however, in reducing waters, and in the presence of sulfur, insoluble ZnS(s) will reduce the dissolved zinc concentration (Young et al. 1980).
Zinc forms complexes with natural DOM, the stability of which are dependent on the pH, the aqueous concentration of zinc and the presence and concentration of other ions in the waters (Florence & Batley 1977). Alkaline conditions favour the formation of Zn-DOM, ZnOH+ and ZnCO3; the latter complex being more prevalent in waters of increased alkalinity (Wilson 1978). In estuarine waters, recent studies suggest that zinc-DOM complexes comprise upwards of 50% of total dissolved zinc (van den Berg et al. 1986, 1987, Muller & Kester 1991). Bruland (1989) has shown that > 98% of dissolved zinc in the surface waters of the North Pacific is complexed by natural organic ligands.
There have been few studies that have investigated the uptake and/or toxicity of zinc in the presence of DOM. Vercauteren and Blust (1996) found that the bioavailability of zinc to the common marine mussel Mytilus edulis, was reduced in the presence of five organic ligands.
Anderson and Morel (1978) demonstrated that organic complexation of natural background levels of zinc in coastal lagoons can limit the growth of diatoms. Morel et al. (1994) postulated that natural oceanic zinc levels might have an effect on global primary production and the carbon cycle.
The removal of zinc from solution via adsorption processes is an important process in natural waters (CCREM 1991). Zinc can sorb to iron, aluminium and manganese (oxy)hydroxides (Lee 1975, Dzombak & Morel 1990), clay minerals (USEPA 1979d) and colloidal organic matter (Tessier et al. 1996). In acidic waters (pH <6) little zinc is expected to (CCREM 1991). As salinity increases, adsorptive capacity is expected to decrease (James & McNaughton 1977).
The uptake and toxicity of zinc decreases with increasing salinity (Nugegoda & Rainbow 1989, Hamilton & Buhl 1990, Bervoets et al. 1996).
Jarvinen and Ankley (1999) report data on tissue residues and effects for zinc for eight freshwater species and six marine species. It is not possible to summarise the data here but readers are referred to that publication for more information.
USEPA (1987b) compiled acute toxicity values of zinc for 43 freshwater species. At a hardness of 50 mg/L, the concentrations ranged from 51 µg/L to 81,000 µg/L. Bacher and O’Brien (1990) found the acute toxicities for Australian freshwater species ranged from 140 µg/L to 6900 µg/L, and Skidmore and Firth (1983) found a range of 340 to 9600 µg/L for ten Australian species. Zinc was found to bioaccumulate in freshwater animal tissues 50 to 1130 times but bioaccumualtion is not generally considered a problem for zinc.
For freshwater guideline derivation, only the chronic data that were linked to pH and hardness measurements were considered and further screened for quality and other factors. This reduced the dataset to around 85 data points. These were adjusted for uniform lower hardness (30 mg/L as CaCO3) and other end-points adjusted to NOECs using the method adapted from van de Plassche et al. (1993). The NOEC values from six taxonomic groups were as follows (pH range 6.75 to 8.39):
Fish: 11 species, 24 µg/L (Oncorhynchus tshawytscha; from LC50) to 1316 µg/L (Ptylocheilus oregonensis; from LC50); seven species had geometric means < 250 µg/L and a measured NOEC of 38 µg/L was reported for Pimephales promelas.
Amphibians: one species, Ambystoma opacum, 180 µg/L (from LOEC).
Crustaceans: three species, 5.5 µg/L (C. dubia; from LC50) to 25.3 µg/L (C. dubia), plus a figure of 18,480 for the crayfish Orconectes virillis).
Insect: one species, Tanytarsus dissimilis, 5 µg/L (NOEC).
Molluscs: three species, 54 µg/L (Dreissena polymorpha) to 11,200 µg/L (Velesunio ambigua), a NOEC of 487 µg/L was measured for Physa gyrina.
Annelid: one species, Limnodrilus hoffmeisteri, 560 µg/L (from LC50).
The geometric means for zinc were distinctly bimodal with two values at least 9.4 times the next highest. However, all the data fitted the model and they were not excluded. The trigger value is above the lowest measured NOEC for an insect and the recalculated NOEC for C. dubia (from chronic LC50 of 27.5 mg/L).
However, given the essential nature of zinc and the fact that the chronic end-points are NOECs, the risk is low and the 95% protection level is considered acceptable for slightly to moderately disturbed systems.
Anderson MA & Morel FMM 1978. Growth limitation of a coastal diatom by low zinc ion activity. Nature 276, 70–71.
ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.
Apte SC & Batley GE 1995. Trace metal speciation of labile chemical species in natural waters and sediments: Non-electrochemical approaches. In Metal speciation and bioavailability in aquatic systems, eds A Tessier & DR Turner, John Wiley & Sons, Chichester, 259–306.
Bacher GJ & O’Brien TA 1990. The sensitivity of Australian freshwater aquatic organisms to heavy metals. SRS 88/018. Victorian Environment Protection Authority, Melbourne.
Bervoets L, Blust R & Verheyen R 1996. Uptake of zinc by the midge larvae Chironomus riparus at different salinities: Role of speciation, acclimation, and calcium. Environmental Toxicology and Chemistry 15, 1423–1428.
Bradley RW & Sprague JB 1985. The influence of pH, water hardness and alkalinity on the acute lethality of zinc to rainbow trout (Salmo gairdneri). Canadian Journal of Fisheries and Aquatic Science 42, 731–736.
Bruland KW 1989. Complexation of zinc by natural ligands in the central north Pacific. Limnology and Oceanography 34, 269–285.
CCREM 1987. Canadian water quality guidelines. Canadian Council of Resource and Environment Ministers, Ontario.
Cheng J, Chakrabarti CL, Back MH & Schroeder WH 1994. Chemical speciation of Cu, Zn, Pb and Cd in rain water. Analytica Chimica Acta 288, 141–156.
Dzombak DA & Morel FMM 1990. Surface complexation modeling: Hydrous ferric oxide. John Wiley & Sons, New York.
Everall NC, Macfarlane NAA & Sedgwick RW 1989. The interactions of water hardness and pH with the acute toxicity of zinc to the brown trout, Salmo trutta L. Journal of Fish Biology 35, 27–36.
Farmer GJ, Ashfield D & Samant HS 1979. Effects of zinc on juvenile Atlantic salmon Salmo salar: Acute toxicity, food intake, growth and bioaccumulation. Environmental Pollution 19, 103–117.
Florence TM & Batley GE 1977. Determination of the chemical forms of trace metals in natural waters, with special reference to copper, lead, cadmium and zinc. Talanta 24, 151–156.
Fromm PO 1980. A review of some physiological and toxicological responses of freshwater fish to acid stress. Environmental Biology of Fishes 5, 79–93.
Hamilton SJ & Buhl KJ 1990. Safety assessment of selected inorganic elements to fry of chinook salmon (Orcorhynchus tshawytscha). Ecotoxicology and Environmental Safety 20, 307–324.
Harrison GI, Campbell PGC & Tessier A 1986. Effects of pH changes on zinc uptake by Chlamydomonas variabilis grown in batch culture. Canadian Journal of Fisheries and Aquatic Sciences 43, 687–693.
Holcombe GW & Andrew RW 1978. The acute toxicity of zinc to rainbow and brook trout. Comparisons in hard and soft water. EPA-600/3-78-094. US Environmental Protection Agency, Washington DC.
James RO & McNaughton MG 1977. The adsorption of aqueous heavy metals on inorganic materials. Geochimica et Cosmochimica Acta 41, 1549–1555.
Jarvinen A W & Ankley G T 1999. Linkage of effects to tissue residues: Development of a comprehensive database for aquatic organisms exposed to inorganic and organic chemicals. SETAC Technical Publication Series, SETAC Press, Pensacola FL.
Lee GF 1975. Role of hydrous metal oxides in the transport of heavy metals in the environment. In Heavy metals in the aquatic environment, ed PA Krenkel, Pergamon Press, Toronto, 137–147.
Morel FMM, Reinfelderm JR, Roberts SB, Chamberlain CP, Lee JG & Yee D 1994. Zinc and carbon co-limitation of marine phytoplankton. Nature 369, 740–742.
Mount DI 1966. The effect of total hardness and pH on acute toxicity of zinc to fish. Air and Water Pollution 10, 49-56.
Mount DI 1986. Principles and concepts of effluent testing. In Environmental Hazard Assessment of Effluents, eds L Bergman, RA Kimerle & AW Maki, Permagon Press, Oxford, 61–65.
Muller FLL & Kester DR 1991. Voltammetric determination of the complexation parameters of zinc in marine and estuarine waters. Marine Chemistry 33, 71–90.
NSW EPA 2000. Analytical Chemistry Section, Table of Trigger Values 20 March 2000, LD33/11, Lidcombe, NSW.
Nugegoda D & Rainbow PS 1989. Effects of salinity changes on zinc uptake and regulation by the decapod crustaceans Palaemon elegans and Palaemonetes varians. Marine Ecology Progress Series 51, 57–75.
Roy R & Campbell PGC 1995. Survival time modeling of exposure of juvenile Atlantic salmon (Salmo salar) to mixtures of aluminium and zinc in soft water at low pH. Aquatic Toxicology 33, 155–176.
Skidmore JF & Firth IC 1983. Acute sensitivity of selected Australian freshwater animals to copper and zinc. Australian Water Resources Council, technical paper 81, Australian Government Publishing Service, Canberra.
Stumm W & Morgan JJ 1996. Aquatic chemistry. 3rd edn, John Wiley & Sons, New York.
Tessier A, Fortin D, Belzile N, DeVitre RR & Leppard GG 1996. Metal sorption to diagenetic iron and manganese oxyhydroxides and associated organic matter: Narrowing the gap between field and laboratory measurements. Geochimica et Cosmochimica Acta 60, 387–404.
USEPA 1995a. Great Lakes water quality initiative criteria documents for the protection of aquatic life in ambient water. US Environmental Protection Agency, Washington DC. EPA-820-B-95-004.
USEPA 1995b. Stay of federal water quality criteria for metals. Federal Register 60, 22228-22237.
USEPA 1987b. Ambient water quality criteria for zinc — 1987. EPA-440/5-87-003. Criteria and Standard Division, US Environmental Protection Agency, Washington, DC.
USEPA 1979d. Zinc. In Water-related environmental fate of 129 priority pollutant, Vol. 1. Introduction, technical background, metals and inorganics, pesticides, polychlorinated biphenyls. United States Environmental Protection Agency, Washington DC. EPA-440/5-80-079.
van de Plassche EJ, Polder MD & Canton JH 1993. Derivation of maximum permissible concentrations for several volatile compounds for water and soil. National Institute of Public Health and Environmental Protection, Report 679101 008, Bilthoven, The Netherlands.
van den Berg CMG, Merks AGA & Duursma EK 1987. Organic complexation and its control of the dissolved concentrations of copper and zinc in the Scheldt Estuary. Estuarine and Coastal Marine Science 24, 785–797.
van den Berg CMG, Buckley PJ, Huang ZQ & Nimmo M 1986. An electrochemical study of the speciation of copper, zinc and iron in two estuaries in England. Estuarine and Coastal Marine Science 22, 479–486.
Vega M, Pardo R, Herguedas MM, Barrado E & Castrillejo Y 1995. Pseudopolarographic determination of stability constants of labile zinc complexes in fresh water. Analytica Chimica Acta 310, 131–138.
Vercauteren K & Blust R 1996. Bioavailability of dissolved zinc to the common mussel Mytilus edulis in complexing environments. Marine Ecology Progress Series 137, 123–132.
Wilson DE 1978. An equilibrium model describing the influence of humic materials on the speciation of Cu2+, Zn2+ and Mn2+ in freshwaters. Limnology and Oceanography 23, 499–507.
Young DR, Jan T-K & Hershelman GP 1980. Cycling of zinc in the nearshore marine environment. In Zinc in the environment, ed JO Nriagu, John Wiley & Sons, New York, 298–335.