Chromium 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 waters, chromium is present mainly in the trivalent chromium (III) and hexavalent, chromium (VI) forms (Hart 1982). The form of chromium present appears to significantly affect toxicity to aquatic organisms and the behaviour of chromium in the aquatic environment. Precipitation of chromium hydroxide is thought to be the dominant removal mechanism for chromium (III) in natural water. Studies in lake water showed that the ratio of chromium (III) to chromium (VI) is affected by the amount of organic matter and dissolved oxygen (Benes & Steinnes 1975). Chromium (VI) is quite soluble, existing in solution as a complex anion. Bioconcentration factors range between 100 and 1000 (CCREM 1987).
Summary of factors affecting chromium toxicity
- Chromium toxicity is affected by valency state: chromium (III) is generally less toxic than chromium (VI). There is equilibrium between the two forms under different conditions.
- Chromium (III) toxicity decreases with increasing hardness and alkalinity. An algorithm is available (Table 3.4.3 and Errata section of the ANZECC & ARMCANZ 2000 guidelines).
- Chromium (VI) toxicity may be hardness-dependent but no algorithms are available.
- Toxicity of chromium (VI) increases in freshwater at lower pH (see Pawlisz et al. 1997).
- Chromium (VI) is not greatly affected by dissolved organic matter or suspended matter.
- Chromium (III) is readily removed from the water column by dissolved organic matter, suspended material or precipitation. Filtration and speciation measurements should account for this.
- Chromium (VI) may bioaccumulate to some degree and chromium (III) may be bioavailable from suspended material.
- Chromium is generally more toxic at high temperatures.
A variety of methods are available for determining the speciation of chromium in water. These include:
- Analytical techniques, such as cathodic stripping voltammetry, chromatography, ion exchange, capillary zone electrophoresis, selective co-precipitation and mass spectrometry (Cranston & Murray 1978, Boussemart & van den Berg 1994, Mach et al. 1996, Semenova et al. 1996, Barnowski et al. 1997)
- Theoretical techniques, such as geochemical modelling (Florence & Batley 1980).
Bioassays are typically used to ascertain metal-organism interactions. These can be coupled with the measured and/or predicted speciation of chromium to determine the bioavailable chromium species. The current analytical practical quantitation limit (PQL) for both chromium (III) and (VI) is 5 µg/L in both fresh and marine water (NSW EPA 2000). Total chromium can be analysed to 0.5 µg/L. Obviously, if total chromium figures were below the trigger value, then the guideline has not been exceeded.
Factors that affect toxicity of chromium
Several studies have shown that the toxicity of both chromium (III) and (VI) to freshwater organisms decreases with increasing water hardness and/or alkalinity [see review by Pawlisz et al. (1997)]. Pickering and Henderson (1966b) reported that the 96-hour LC50 for Cr (III) to the fathead minnow (Pimephales promelas) in soft water (hardness, 20 mg/L as CaCO3; pH 7.5) was 5.1 mg/L. In contrast, in hard water (hardness, 360 mg/L as CaCO3; pH 8.2) it was 67.4 mg/L. Using the same species and conditions, they found that the 96-hour LC50 for Cr (VI) was 17.6 mg/L in soft water compared to 27.3 mg/L in hard water. An exponential, inverse relationship has been shown to exist between water hardness and the uptake and toxicity of chromium (III). An algorithm describing this relationship has been used to calculate a hardness-modified chromium (III) guideline value for protecting aquatic ecosystems in North America (USEPA 1995a,b). There were insufficient data for USEPA (1985g) to develop an algorithm based on water hardness for Cr (VI).
Few data are available on the effects of natural dissolved organic matter on the toxicity of chromium (VI). Wilson and Al-Hamdani (1997) showed that humic substances slightly reduced the toxicity of chromium (VI) to Azolla caroliniana.
Toxicity of chromium (VI) typically decreased as salinity and sulfate concentrations in seawater increased (Pawlisz et al. 1997). Frey at al (1983) found that concentrations that inhibited natural phytoplankton populations in an Oregon estuary increased 10-fold as salinity increased from 0.04 to 32.5%. Similar findings have been reported for bivalves, crustaceans, rotifers and polychaete worms (Frank & Robertson 1979, Bryant et al. 1985a, Riedel 1985, McLusky & Hagerman 1987).
Maximum toxicity of Cr (VI) to Selenastrum growth was found at pH 4, with least toxicity in the range pH 8 to 10 (Michnowicz & Weaks 1984). In contrast, Cr (VI) was more toxic to growth and multiplication of duckweed at high pH compared to low pH (Nasu & Kugimoto 1980).
Cr (VI) is usually more toxic than Cr (III). Pawlisz et al. (1997) reported that the lowest freshwater acute toxicities for Cr (III) were 3300 µg/L for fish and 1200 µg/L for Daphnia magna, in comparison to Cr (VI) with 220 µg/L for fish and 5.3 µg/L for Ceriodaphnia dubia. Chronic toxicities for Cr (III) in freshwater ranged from 6 µg/L for fish (Oncorhynchus mykiss) and 600 µg/L for invertebrates in comparison with Cr (VI) with 10 µg/L for both fish and invertebrates (Pawlisz et al. 1997). Freshwater organisms are generally much more sensitive to chromium than marine organisms. USEPA (1985g) reported the range of acute toxicity data for chromium (VI) in 27 genera of freshwater animal species from 23 µg/L for a cladoceran to 1870 µg/L for a stonefly. All five species of daphnids tested were especially sensitive.
Freshwater algae and invertebrates are more sensitive to chromium (VI) than fish, with Cr (VI) being the most toxic species. Crustaceans are particularly sensitive to Cr (VI), with 3-day LC50 values for D. magna between 30 and 81 µg/L, and chronic values from 2.5 to 40.0 µg/L (Trabalika & Gehrs 1977). Hickey (1989) reported a 24-hour EC50 (immobilisation) for the New Zealand C. dubia of 5.3 µg/L for Cr (VI) and a chronic 14-d LOEC of 10 µg/L. The 48-hour EC50 for Moina australiensis was 22.5 to 36.1 µg/L (Krassoi & Julli 1994). Growth rate of the freshwater green alga Chlorella protothecoides was also sensitive to Cr (VI), with a 72-hour EC50 of 100 µg/L. The freshwater alga Selenastrum capricornutum had a 72-hour EC50 of 470 µg Cr (VI)/L, with no effect at concentrations below 5 µg/L (Stauber et al. 1994b).
Pawlisz et al. (1997) also reported marine toxicity data for chromium. Cr (III) caused sperm damage to marine O. mykiss at 5 µg/L and filtering rate of the mussel Perna perna was affected (EC50) at 2 µg/L. The lowest acute EC50 reported for Cr (III) was 1600 µg/L for nauplii of Tisbe battagliai over 96 hours. The 7-day LOEC for reproduction of this species was 320 µg/L.
For Cr (VI), Pawlisz et al. (1997) reported marine acute toxicities to Australian crab Portunus pelagicus of 1300 mg/L and to the Australian amphipod Allorchestes compressa of 5560 µg/L. Several other species had similar toxicities. The most sensitive fish was flatfish Citharichthys stigmaeus with a 21-day LC50 of 5000 µg/L. Short-term (2 to 4 days) acute toxicities to marine fish were all above 16,000 µg/L.
There were limited Australasian data on the toxicity of Cr (VI) to marine organisms. Cr (VI) is much more toxic to marine organisms than Cr (III). For example, the diatom Nitzschia closterium, isolated from estuarine waters near Sydney at 33‰ salinity, had a 72-hour EC50 of 2.4 mg/L for Cr (VI), compared to a 72-hour EC50 of >5.0 mg/L for Cr (III) (Florence & Stauber 1991). Fertilisation of the macroalga Hormosira banksii, isolated from Port Phillip Bay, was insensitive to Cr (VI), with an EC50 of 360 mg/L. In studies with the Australian sand crab Portunus pelagicus, deleterious sub-lethal effects were found at Cr (VI) concentrations of 300 µg/L (Mortimer & Miller 1994) while the 96-hour LC50 for the Tasmanian blenny, a tidepool fish, was reported as 2.6 µg/L (Stauber et al. 1994a).
In marine and estuarine conditions, the high sulfate concentrations make chromium toxicity unlikely, except at very polluted sites. In freshwaters of low pH, low hardness and with low sulfate concentrations, Cr (VI) concentrations could adversely affect ecosystems.
Freshwater guideline—Cr (III)
Chronic data on chromium (III) were screened for hardness and other standard factors to give 7 data points. Hardness has a significant influence on the toxicity, with chromium (III) being more toxic in soft water. The pH range was 7.2 to 8.0. These figures were corrected to a common hardness value of 30 µg/L as CaCO3 to give the following figures:
Fish: three species, 7 to 28-day LC50, 66 (O. mykiss) to 442 µg/L (Micropterus salmoides)
Amphibians: one species, Ambystoma opacum, 8-day LC50, 795 µg/L.
Crustaceans: one species, D. magna, 21-day EC50, reproduction, 430 µg/L.
Algae: one species, Selenastrum capricornutum, 4-day EC50, population growth, 397 µg/L. A hardness value for this figure could not be found but USEPA (1986) reported that it was in soft water.
The screening process reduced acceptable chronic data to six species from three taxonomic groups, and acute data for species from two taxonomic groups. Hence only a low reliability trigger value could be calculated.
A low reliability freshwater trigger value for chromium (III) of 3.3 µg/L was derived using the assessment factor (AF) method (a factor of 20 was applied to the lowest, O. mykiss figure, from a limited set of chronic data). This applies to low hardness water at 30 mg/L as CaCO3. This figure should only be used as an indicative interim working level.
Marine guideline—Cr (III)
Marine acute data (12 points) were available for chromium (III) for 4 taxonomic groups, as follows:
Fish: two species, 72 to 96-hour LC50, 900 to 53,000 µg/L.
Crustaceans: one species, Acartia clausi, 48-hour LC50, 19,270 µg/L.
Molluscs: one species, Crassostrea virginica, 48-hour LC50, 10,300 µg/L.
Annelids: one species, Ophrotrocha diadema, 48-hour LC50, 100,000 µg/L.
Algae: one species, Ditylium brightwellii, 5-day EC50 (photosynthesis), 2000 µg/L.
A marine moderate reliability trigger value for chromium (III) of 10 µg/L was derived, using the statistical distribution method with 95% protection and an acute-to-chronic ratio (ACR) of 77.6.
Freshwater guideline—Cr (VI)
A total of 222 chronic data points were available for chromium (VI) in freshwater, comprising 7 taxonomic groups. Chronic data were converted to a uniform NOEC end-point, using the method adapted from van de Plassche et al. (1993) to give the following figures (expressed as geometric means for species and end-points, except where indicated) (pH range was 7.0 to 8.2):
Fish: 13 species, 84 to 35,314 µg/L. The lowest figure was from a chronic LC50 for channelfish, Nuria danrica, to give a NOEC of 61 mg/L.
Crustaceans: four species, 2.8 µg/L (C. dubia) to 50,000 µg/L (D. carinata). The lowest figure was from a chronic LC50 for C. dubia.
Rotifer: one species, Philodina roseola, 880 to 6200 µg/L (range).
Algae, diatoms and blue-green algae: nine species, 0.1 (Stephanodiscus sp.) to 600 µg/L Chlorella vulgaris). Most species had means >30 µg/L. A recent Canadian publication (Pawlisz et al. 1997) cited data from around 20 algal species but any additional data could not be included until assessed according to the selection criteria. The trigger value is above the outlying diatom figure but is considered sufficiently protective of most species.
Flagellates: two species, 23 µg/L (Euglena gracilis; from LC50) to 600 µg/L.
Macrophytes: two species, 16 µg/L, from an EC50, growth, (Lemna minor) to 920 µg/L (Myriophyllum sp.), from EC50, growth figures.
A freshwater high reliability trigger value for chromium (VI) of 1.0 µg/L was derived using the statistical distribution method at 95% protection.
After screening, over 225 marine data points were obtained for chromium (VI), comprising the following, reported as geometric means of species and end-points after conversion to NOEC equivalents:
Fish: three species, 776 µg/L (Citharichthys sp., from 14 to 21-day LC50) to 14,125 µg/L (Cyprinodon variegatus, from NOEC, growth).
Crustaceans: 13 species, 4 µg/L (Cancer anthonyi, from 7-day LOEC, hatch) to 3090 µg/L (Rhithanopanopeus sp., from 20-day LC50).
Echinoderm: one species, Asterias forbesi, 2000 µg/L, from 7-day LC50.
Mollusc: three species, 1600 µg/L (Mya arenaria, from 7-day LC50) to 10,000 µg/L (Macoma balthica, from 8-16-d LC50).
Annelids: four species, 2.5 µg/L (Neanthes sp., from 14-day LOEC, mortality) to 1995 µg/L (Dinophilus sp., from 7-day LOEC, mortality).
Sipunculid: one species, Themiste sp., 1995 µg/L, from 11 to 52-day LC50.
Algae, blue–green algae, and flagellates: 7 species, 4.8 µg/L (a dinoflagellate, from 7-day EC50, growth) to 1000 µg/L (Skeletonema sp, NOEC, population growth).
A marine high reliability trigger value for chromium (VI) of 4.4 µg/L was derived using the statistical distribution method at 95% protection.
The guideline figure is close to the geometric mean of three out of 36 species (4.0, 4.8 and 5.0 µg/L) but, as these were NOEC figures, the 95% protection value should be sufficiently protective in most slightly to moderately disturbed systems.
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