Cadmium in freshwater and marine water
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
In natural surface waters, cadmium occurs predominantly in the divalent form, comprising several inorganic and organic compounds (Reeder et al. 1979). The solubility of dissolved cadmium decreases with increasing pH and alkalinity (French 1986). Low background levels of cadmium are found in many natural waters (Table 8.3.2 in the ANZECC & ARMCANZ 2000 guidelines).
Cadmium may be accumulated by a number of aquatic organisms, with bioconcentration factors in the order of 100 to 100,000 (Reeder et al. 1979).
Summary of factors affecting cadmium toxicity
- Cadmium toxicity is hardness-dependent and an algorithm is available (Table 3.4.3 in the ANZECC & ARMCANZ 2000 guidelines).
- Cadmium is less toxic in freshwater at lower pH, although toxicity is reduced above pH 8 (algorithms should account for this).
- Dissolved organic matter reduces cadmium toxicity. The effect of organic complexation requires experimental determination.
- Cadmium is absorbed strongly by suspended material. Filtration and speciation measurements should account for this.
- Cadmium complexes with chloride, resulting in reduced toxicity at higher salinity.
- Cadmium has a variable tendency to bioaccumulate but bioconcentration can be significant for bivalves in marine and estuarine situations.
A variety of methods are available for determining the speciation of cadmium in water. These include:
- Analytical techniques, such as physical separation (e.g. [ultra]filtration, dialysis, centrifugation), potentiometry (e.g. ion-selective electrode), voltammetry (e.g. anodic stripping voltammetry), ion exchange and chromatography (Florence & Batley 1980, Holm et al. 1995, Apte & Batley 1995)
- Theoretical techniques, such as geochemical modelling (Mantoura et al. 1978, French 1986, Paalman et al. 1994, Holm et al. 1995).
Bioassays are typically used to ascertain metal-organism interactions. These can be coupled with the measured and/or predicted speciation of cadmium to determine the bioavailable cadmium species. The current analytical practical quantitation limit (PQL) for cadmium is 0.05 µg/L in fresh water and 1.0 µg/L in marine water (NSW EPA 2000).
Factors that affect the bioavailability and toxicity of cadmium
It is generally considered that the free cadmium ion (Cd2+) is the form of cadmium primarily responsible for eliciting a toxic response in aquatic organisms (Campbell 1995) and is the predominant species of dissolved cadmium in fresh surface waters at pH ≤8.5 (Moore & Ramamoorthy 1984a, French 1986). Cadmium complexes with inorganic and/or organic ligands/agents generally reduce the uptake and toxicity of the metal by reducing the concentration of Cd2+. Cadmium typically forms weak complexes with natural dissolved organic matter (DOM) in fresh and marine waters (Moore & Ramamoorthy 1984a, Marinsky et al. 1985). In waters with a high natural DOM content, sorption of cadmium to organic matter and other complexing agents can be important (Tessier et al. 1996). The formation of cadmium-DOM complexes is usually greatest under conditions of low hardness and alkalinity, neutral pH and high natural DOM (Giesy 1980). Redox potential is believed to have little direct influence on cadmium speciation.
Sorption to clay, mineral and biotic surfaces is probably the most important process for the removal of cadmium from solution (Dzombak & Morel 1990, Majidi et al. 1990, Goldberg et al. 1996). Sorption of cadmium to particles and organic matter increases with pH, until a threshold point is reached, usually around pH 8 (Dzombak & Morel 1990, Wagemann et al. 1994). The sorption of cadmium to particles and organic matter typically declines with increasing salinity (Greger et al. 1995). Conflicting results have been reported on the bioavailability of cadmium adsorbed to suspended particles. Some studies have shown that the bioavailability of cadmium is similar for both the dissolved phase and particulate phases (Cossa 1988). Such differences are dependent on the feeding habit (e.g. filter feeding) of the organism, as well as the water and sediment chemistry.
It is well established that the uptake and toxicity of cadmium in freshwater organisms decreases with increasing water hardness and alkalinity [see reviews by Sprague (1987), Spry & Wiener (1991) and Wren et al. (1995)]. For example, Palawski et al. (1985) reported that the 96-hour LC50 for striped bass (Morone saxatilis) was 3.7 µg Cd/L in soft water (40 mg/L as CaCO3; alkalinity, 30 mg/L as CaCO3; pH 8.1). In contrast, it was 27.0 µg Cd/L in hard water (285 mg/L as CaCO3; alkalinity, 262 mg/L as CaCO3; pH 7.9). An exponential, inverse relationship has been demonstrated between water hardness and the uptake and toxicity of cadmium. An algorithm describing this relationship has been used to calculate a hardness-modified cadmium guideline value for protecting aquatic ecosystems in North America (USEPA 1995a,b).
The uptake and toxicity of cadmium in freshwater organisms generally decreases with decreasing pH (i.e. increasing H+ concentration) (e.g. Peterson et al. 1984, Cusimano et al. 1986, Krantzberg & Stokes 1988, Schubauer-Berigan et al. 1993) over the pH range 3.5 to 8.5. In contrast, Gerhardt (1992) showed a negligible change in the toxicity of cadmium to three freshwater invertebrates over the pH range 5 to 7.
In seawater, dissolved cadmium is dominated by chloride-complexes (Fergusson 1990). The formation of cadmium–chloride complexes declines with decreasing salinity (i.e. chloride concentration), until the free hydrated ion (Cd2+) becomes dominant at ≤2‰ (Raspor 1980). It has been generally established that the uptake and toxicity of cadmium in aquatic organisms increases with decreasing salinity, that is, more estuarine situations (Mayer et al. 1989, Gossiaux et al. 1992, de Lisle & Roberts 1994, Wang et al. 1996). Variation of toxicity with temperature seems to be species-specific (USEPA 1986). The chronic data available appear to reflect the effects of salinity and temperature (USEPA 1986).
Cossa (1988) reported results of a worldwide survey of cadmium in mussel Mytilus edulis tissue, with regional concentrations varying from 0.6 to 3.3 mg/kg. The concentration factor between the mussel and its environment was between 10,000 and 20,000. Reliable seawater concentrations from seven regions allowed development of a relationship between cadmium concentrations in seawater (Cdsw; mg/L) and in mussel tissue (Cdm; mg/kg):
Cdm = 0.74 Cdsw + 0.39
Concentrations of cadmium in the Gironde Estuary in France of between 0.2 mg/L and 0.4 mg/L were associated with mussel concentrations of between 12 mg/kg and 37 mg/kg. Based on the then proposed maximum Cd concentration of 10 mg/kg for human consumption, Cossa (1988) derived a maximum water concentration of around 0.2 µg/L.
Long et al. (1997) reported the accumulation of cadmium in two species of Australian dolphin and their prey. Cadmium accumulated in kidney up to 38 mg/kg and levels in 32% of dolphins in southern Australia were associated with histopathological lesions. This indicates the potential for cadmium to cause secondary poisoning in marine systems.
Jarvinen and Ankley (1999) report data on tissue residues and effects for 35 freshwater species and 25 marine species. It is not possible to summarise the data here but readers are referred to that publication for more information. Ward (1982) reported that Sydney rock oyster exposed to 25 µg/L of cadmium chloride accumulated between 48 and 72 mg/kg wet weight, resulting in 100% mortality after 60 days. Exposure to 10 µg/L for 112 days had no effect on survival and tissue concentrations around 25 mg/kg.
Acute toxicity of cadmium to freshwater animal species in 44 genera ranged from 1 µg/L for rainbow trout to 28,000 µg/L for mayfly (USEPA 1986). CCREM (1987) noted that the species mean acute toxicity value for rainbow trout was 3.6 µg/L. The acute values for 30 marine invertebrates ranged from 15.5 µg/L upward (USEPA 1985f). Cadmium up to 200 µg/L did not inhibit fertilisation success of gametes from Australian scleractinian reef corals (Reichelt-Brushett & Harrison 1999).
A total of 73 chronic data points were available for cadmium, after screening for quality, for values associated with hardness measurements and for other reasons listed in Section 126.96.36.199 in the ANZECC & ARMCANZ (2000) guidelines. These were adjusted for low hardness (30 mg/L as CaCO3) and other end-points were also adjusted to NOECs using the method adapted from van de Plassche et al. (1993). They comprised the following (expressed as geometric means of NOECs for species and end-points adjusted for low hardness):
Fish: nine species, geometric means ranged from 0.49 µg/L (Oncorhynchus tshawytscha; adjusted fromLC50) to 767 µg/L for Salmo salar. The lowest measured chronic figure (hardness-corrected) was 0.5 µg/L for O. mykiss (LOEC).
Amphibians: one species, Ambystoma opacum, NOEC (mortality) of 10.2 µg/L.
Crustaceans: six species, geometric means for species and end-points ranged from 0.08 µg/L for Daphnia magna to 3.2 µg/L for Asellus aquaticus, although the crayfish Orconectes virillis, had a NOEC (geometric mean) of 122 µg/L.
Insects: two species, means for NOECs of 0.52 to 0.82 µg/L.
Algae: three species, means for NOECs of 8.2 to 32 µg/L.
A high reliability freshwater trigger value of 0.2 µg/L was derived for cadmium using the statistical distribution method at 95% protection. This figure applies to a low hardness of 30 mg/L as CaCO3. The 95% protection level was above the geometric mean for NOECs for D. magna. It is not, however, above any experimental chronic figure but several chronic LC50s or NOECs were around 0.3 to 0.6 µg/L, after correction for low hardness. The 95% protection level was considered sufficiently protective for most such systems. If water managers are concerned about related species, the 99% protection level (0.06 µg/L) could be used for slightly to moderately disturbed ecosystems, but users are advised to check the spread of data (Section 8.3.7 in the ANZECC & ARMCANZ 2000 guidelines).
After screening, a total of 175 chronic data points comprising eight taxonomic groups, were available for cadmium in the marine environment. These consisted of a variety of end-points and were corrected to NOEC equivalents using the method described previously. The NOEC data varied as follows:
Fish: six species, 108 µg/L (Menidia menidia, from 19-day LC50) to 16,000 µg/L (Tilapia mossambica, 7-d LC50)
Crustaceans: 19 species, 0.45 µg/L (Mysidiopsis bahia, from 18-day MATC, growth of 0.9 µg/L) to 10,400 (Uca pugilator, 8-day LC50). Geometric means below 25 µg/L were encountered for six species for at least one end-point. The geometric mean for M. bahia growth was 2.75 µg/L.
Echinoderms: one species, Asterias forbesi, 140 µg/L, from 7-day LC50.
Molluscs: five species, 30 mg/L (Mya arenaria, from 7-day LC50) to 3200 µg/L (Nassarius obsoletus), although only the gastropod had values >600 µg/L.
Annelids: five species, 7.8 µg/L (Neanthes arenaceodentata, from 28-day LC50) to 1302 µg/L.
Nematodes: one species, Monhystera disjuncta, 400 to 10,000 µg/L.
Rotifers: one species, Brachionus plicatilis, 3-day LC50, 1040 µg/L.
Algae: two species, 5.7 µg/L (Champia parvula, from 14-day MATC, reproduction) to 1780 µg/L (Skeletonema costatum, from 10-day EC50, population growth).
A high reliability marine guideline value for cadmium of 5.5 µg/L was calculated using the statistical distribution method with 95% protection. The 99% protection level is 0.7 µg/L, and is recommended for slightly to moderately disturbed ecosystems. The 95% protection level was above the geometric mean of NOECs for several marine crustaceans. To protect against chronic toxicity to related species and bioaccumulation of cadmium, use of the 99% protection level (0.7 µg/L) is recommended for slightly-moderately disturbed ecosystems. If in an area where shellfish are likely to be used for human consumption, the trigger value should be reduced to 0.2 µg/L.
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