Zinc :: all ecosystems

Ecosystems: 

Key Concerns

Symptoms of zinc toxicity in plants include reduced root growth, and inhibition of various physiological processes including transpiration, respiration and photosynthesis. Stunted growth, leaf epinasty and chlorosis of younger leaves are characteristic of zinc toxicity (WHO 2001). Reduced yield, and chlorosis have been reported in various crop species, including fescues, blue grass, barley, soybean, lettuce and cyperus grown in soil with high zinc concentrations (Chaney 1993). 

However, large variations in inter-species sensitivity and bioavailability of the zinc must be taken into account when assessing possible effects. The concentration of total zinc is not necessarily indicative of the bioavailble fraction. The bioavailability of zinc is determined by various factors, including the chemical speciation of the zinc, and the characteristics of the soil, including its pH and the concentrations of inorganic and organic ligands, and competition with other chemical species (WHO 2001).

Ecosystem specific information

Arable habitats – high levels of zinc have been reported in wheat (Triticum aestivum) and corn (Zea mays) grown near non-ferrous mining and smelting bases (Nan et al. 2002). Some plants have been shown to tolerate soils with high zinc concentrations; the grasses Agrostis capillaries and Festuca rubra which were sown near a zinc smelter could tolerate soil zinc concentrations up to 16000 mg/kg (Bouwman et al. 2001). Laboratory studies have demonstrated effects on nematode communities indigenous to agricultural soil. Exposure to zinc concentrations exceeding 50 mg/kg soil caused the disappearance of some nematode taxa (Korthals et al. 2000).

Bogs, wetland and heath – effects on plant biomass, density and diversity have been reported for various species of grass growing on floodplains in the vicinity of sites previously used for mining. The zinc threshold concentration for the decrease in diversity of the floodplain grass communities was 170 mg/kg soil (Stoughton and Marcus 2000). Some wetland plants such as Typha latifolia and Phragmites australis contain the ability to tolerate soils with high zinc concentrations,(McCabe et al. 2001).

Coastal and rocky habitat – zinc has been shown to exert adverse reproductive, biochemical, physiological and behavioural effects on a variety of saltwater organisms at concentrations exceeding 50 µg/l (WHO 2001). Large variations in inter-species sensitivity and bioavailability of the zinc must be taken into account when assessing possible effects. The concentration of total zinc is not necessarily indicative of the bioavailable fraction. The bioavailability of zinc is determined by various factors, including the chemical speciation of the zinc, and the characteristics of the water, including its pH, salinity and the concentrations of inorganic and organic ligands, and competition with other chemical species (WHO 2001).

Minimum thresholds for adverse effects of dissolved zinc on aquatic organisms are as follows (WHO 2001):

  • 50-100 µg/l: acute effects on mysids
  • 100-200 µg/l: acute effects on fish
  • 200-1000 µg/l: acute effects on amphipods and decapods
  • 1000-10000 µg/l: acute effects on polychaetes and molluscs

Toxicity data is also available for marine algae, but this was not considered of sufficient quality for inclusion in the threshold concentrations listed above (WHO 2001). EC50 values, for culture growth, based upon acute exposure periods of either 72 or 96 hours, ranged from 58 to 271 µg/l (Rosko and Rachlin 1975; Fisher and Jones 1981; Stauber and Florence 1990).

Freshwater – zinc has been shown to exert adverse reproductive, biochemical, physiological and behavioural effects on a variety of freshwater organisms at concentrations exceeding 20 µgl (WHO 2001). Large variations in inter-species sensitivity and bioavailability of the zinc must be taken into account when assessing possible effects. The concentration of total zinc is not necessarily indicative of the bioavailable fraction. The bioavailability of zinc is determined by various factors, including the chemical speciation of the zinc, and the characteristics of the soil, including its pH and the concentrations of inorganic and organic ligands, and competition with other chemical species (WHO 2001).

Minimum thresholds for adverse effects of dissolved zinc on aquatic organisms are as follows (WHO 2001):

  • 20-50 µg/l chronic effects on cladocerans in soft water (water with hardness <100 mg CaCO3 / litre).
  • 50-100 µg/l chronic effects on cladocerans in hard water (water with hardness >100 mg CaCO3 / litre), acute effects of cladocerans in soft water, acute and chronic effects on fish in soft water and chronic effects on freshwater insects.
  • 1000-10000 µg/l acute effects on molluscs, copepods and amphipods, and acute effects on fish in hard water.

Toxicity data is also available for freshwater algae and plants, but this was not considered of sufficient quality for inclusion in the threshold concentrations listed above (WHO 2001). 72 Hour-EC50 values for growth of freshwater algae (Scenedesmus quadricauda) range from 150 to 170 µg dissolved Zn/l, with corresponding No Effect Concentrations of 30 to 50 µg/l (Van Ginneken 1994; Van Woensel 1994). Toxicity in aquatic plants has been reported following exposure to zinc concentrations ranging from 8100 to 67700 µg/l (Brown and Rattigan 1979; Dirilgen and Inel 1994).

Grassland – symptoms of zinc toxicity in plants include reduced root growth, and inhibition of various physiological processes including transpiration, respiration and photosynthesis. Stunted growth, leaf epinasty and chlorosis of younger leaves are characteristic of zinc toxicity (WHO 2001). Some plants have been shown to tolerate soils with high zinc concentrations; the grasses Agrostis capillaries and Festuca rubra which were sown near a zinc smelter could tolerate soil zinc concentrations up to 16000 mg/kg (Bouwman et al. 2001). However, other plants grown in the vicinity of zinc smelters demonstrated phtotoxicity, leading to the disappearance of most species of vegetation, with the exception of some zinc resistant grasses and ragweed (Ambrosia artemisiifolia) (Li et al. 2000).

Woodland and hedgerow - symptoms of zinc toxicity in plants include reduced root growth, and inhibition of various physiological processes including transpiration, respiration and photosynthesis. Stunted growth, leaf epinasty and chlorosis of younger leaves are characteristic of zinc toxicity (WHO 2001). High zinc concentrations have been reported in the leaves of trees growing near sites where zinc ore is mined or processed (Pugh et al. 2002). Adverse effects, including reductions in body growth, biomass and diversity have also been reported in enchytraeid worms from coniferous forests polluted with zinc (Salminen et al. 2001b), with complete extinction at zinc soil concentrations exceeding 2393 mg/kg dry weight (Salminen et al. 2001a). Similar effects have also been found in earthworms, resulting in a reduction in the incorporation of organic matter into woodland soils contaminated with zinc (Beyer 2001). Woodland habitats, containing scots pine and birch and oak have been used as shelterbelts beside major roads, with entrapment of the metals, including zinc, released from vehicles, and subsequ ent soil enrichment (Heath et al. 1999).

Large variations in inter-species sensitivity and bioavailability of the zinc must be taken into account when assessing possible effects. The concentration of total zinc is not necessarily indicative of the bioavailable fraction. The bioavailability of zinc is determined by various factors, including the chemical speciation of the zinc, and the characteristics of the soil, including its pH and the concentrations of inorganic and organic ligands, and competition with other chemical species (WHO 2001).

Additional Comments

Zinc is an essential element for all biota, therefore any adverse effects must be balanced against its essentiality. This means that for all organisms, there will be range of optimal zinc concentrations. Exposure to zinc concentrations outwith this range, will result in adverse effects, due to either zinc deficiency, or zinc toxicity.

Environmental limit: 

Critical Load/ Level

No estimate available

References: 

Bouwman, L. A.; Bloem, J ; Romkens, P. F.A.M.; Boon, G. T.; Vangronsveld, J 2001 Beneficial effects of the growth of metal tolerant grass on biological and chemical parameters in copper and zinc contaminated sandy soils Minerva Biotecnologica 9-26
Brown, B. T.; Rattigan, B. M. 1979 Toxicity of soluble copper and other metal ions to Elodea canadensis. Environmental Pollution 303-314
Chaney, R. L. 1993 Zinc Phytotoxicity In A. D. Robson Proceedings of the International Symposium on Zinc in Soil and Plants 135-150
Dirilgen, N ; Inel, Y 1994 Effects of zinc and copper on growth and metal accumulation in duckweed, Lemna minor Bulletin of Environmental Contamination and Toxicology 442-449
Fisher, N. S.; Jones, G. J. 1981 Heavy metals and marine phytoplankton: correlation of toxicity and sulfhydryl-binding Journal of Phycology 108-111
Heath, B. A.; Maughan, J. A.; Morrison, A. A.; Eastwood, I. W. 1999 The influence of wooded shelterbelts on the deposition of copper, lead and zinc at Shakerley Mere, Cheshire, England Science of the Total Environment 415-417
Korthals, G. W.; Bongers, M ; Fokkema, A ; Dueck, T. A.; Lexmond, T. M. 2000 Joint toxicity of copper and zinc to a terrestrial nematode community in an acid sandy soil Ecotoxicology 219-228
Li, Y. M.; Chaney, R. L.; Siebielec, G ; Kerschner, B. A. 2000 Response of four turfgrass cultivars to limestone and biosolids-compost amendment of a zinc and cadmium contaminated soil at Palmerton, Pennsylvania Journal of Environmental Quality 1440-1447
McCabe, O. M.; Baldwin, J. L.; Otte, M. L. 2001 Metal tolerance in wetland plants Minerva Biotecnologica 141-149
Nan, Z ; Li, J ; Zhang, J ; Cheng, G 2002 Cadmium and zinc interactions and their transfer in soil-crop system under actual field conditions Science of the Total Environment 187-195
Pugh, R. E.; Dick, D. G.; Fredeen, A. L. 2002 Heavy metal (Pb, Zn, Cd, Fe and Cu) contents of plant foliage near the Anvil Range lead/zinc mine, Faro, Yukon Territory Ecotoxicology and Environmental Safety 273-279
Rosko, J. J.; Rachlin, J. W. 1975 The effect of copper, zinc, cobalt and manganese on the growth of the marine diatom Nitzschia closterium Bulletin of the Torrey Botanical Club 100-106
Salminen, J ; Anh, B. T.; Van-Gestel, C. A.M. 2001 Indirect effects of zinc on soil microbes via a keystone enchytraeid species Environmental Toxicology and Chemistry 1167-1174
Stauber, J. L.; Florence, T. M. 1990 Mechanism of toxicity of zinc to the marine diatom Nitzschia closterium Marine Biology 519-524