Chromium is beneficial, but not essential to growth in higher plants (Eisler 1986). As a naturally occurring element, chromium is ubiquitous in the environment, although background concentrations in soil are generally low, ranging from 2 to 60 mg/kg (WHO 1988). The concentration of total chromium in soil is not indicative of bioavailable chromium (NRCC 1976; WHO 1988). The bioavailability of chromium is affected by various factors, including the pH of the soil, interactions with other minerals and/or organic chelating compounds, and the concentrations of carbon dioxide and oxygen (WHO 1988). Trivalent chromium sorbs to various ligands and forms insoluble entities which are not bioavailable. Hexavalent chromium forms many soluble salts that are bioavailable, and therefore able to cross membranes and induce toxic responses (Pawlisz et al. 1997). Almost all hexavalent chromium compounds in the environment are a result of anthropogenic activities (WHO 1988).
Ecosystem specific information
Arable habitats - many fertilisers contain appreciable amounts of chromium, with concentrations up to 300 mg/kg reported in some nitrogen fertilisers (NRCC 1976). Therefore arable soils which have received repeated fertiliser applications may have high soil chromium concentrations. Inhibited growth of swiss chard has been reported following application of 10% and 15% solutions of fertilizer which contained 5900 mg Cr/kg dry weight (Grubinger et al. 1994). Similarly, soils which have received sewage sludge applications may also have high chromium concentrations. However annual treatments with sewage sludge containing chromium concentrations of 8800 mg/kg dry solids (at an application rate of 1100 kg Cr/ha) did not affect the yields of winter wheat, and winter beans (Bhogal et al. 2003).
Some effects in plants have been reported following exposure to chromium solutions. For hexavalent chromium, reduced growth was reported in lettuce (lactuca sativa) exposed to 0.16 mg/l, with a corresponding NOEC of 0.04 mg/l (Adema and Henzen 1989). Sage (Salvia sclarea) is also sensitive to chromium, with reduced root elongation reported at 1.0 mg/l (Corraddi et al. 1993). Other plants are less sensitive, for example, no effects on the growth of sweet orange were reported at 75 mg/l (Pawlisz et al. 1997). For trivalent chromium, the toxicity to plants ranges from 0.104 mg/l (reduced growth of oat roots) to 50 mg/l (stunted growth of corn and tomato) (Pawlisz et al. 1997).
Bogs, wetland and heath - bioaccumulation of chromium by sphagnum moss has been shown to be a passive process, with accumulation equal in living and dead mosses (Gstoettner and Fisher 1997). The concentration of chromium in the moss was correlated with the concentration of chromium in the bog water.
Coastal and rocky habitat – the toxicity of cadmium to saltwater invertebrates has been classified as ranging from moderately toxic to highly toxic, with acute LC50 values ranging from 0.03 to 165 mg/l (WHO 1992). The most sensitive marine organisms are decapod crustaceans such as grass shrimp (Palaemonetes vulgaris), hermit crab (Pagurus longicarpus) and sand shrimp (Crangon crangon), with LC50 values ranging from 0.32 to 0.42 mg/l (Eisler 1985). Acute LC50 values for fish ranged from 0.31 to 59 mg/l (WHO 1992). Cadmium has also been shown to affect reproduction. Development of starfish (Asterias rubens) embryos was affected at 25 µg/l. This concentration also affected maturation of oocytes, although no effects on spermatozoa were reported (Den Besten et al. 1989). Growth of Atlantic salmon (Salmo salar) alevins was significantly reduced at 0.47 µg/l (Rombough and Garside 1982). Effects on renal physiology have been reported in seabirds with high cadmium concentrations (Nicholson et al. 1983; Nicholson and Osborn 1983).
Grassland - the concentration of chromium in ryegrass (Lolium multiflorum) grown in soil amended with either inorganic chromium salts or sewage sludge increased with increasing soil concentration. Uptake of chromium by plants was greater in soils with added chromium salts compared to those which had chromium added as sewage sludge. However, no effect on plant growth was reported at chromium concentrations up to the maximum soil concentration of 100 mg/kg (Loch et al. 1993).
Woodland and hedgerow – reduced plant cover was reported in a woodland area adjacent to a tannery, although the chromium exposure was due to the disposal of tannery effluent, rather than airborne deposition. All three tree species (Indian rosewood, Dalbergia sissoo, Gum acacia Acacia arabica and Robusta cottonwood Populus euroamericana) growing on the contaminated site had arbuscular mycorrhizal fungal infection in their roots, and arbuscular mycorrhizal fungal propagules in the associated rhizosphere (Khan 2001).
Concentrations of chromium in lichen (Parmelia sulcata) sampled from olive trees at various sites throughout Portugal were frequently reported to be in the range of 5 to 30 mg/kg (Freitas et al. 1999) which has previously been suggested to be toxic to plants (Kabata-Pendias and Pendias 1984). Airborne emissions of chromium may be taken up by woodland mosses such as Isothecium stoloniferum, although concentrations do not necessarily demonstrate local gradients, with reference to sources (Pott and Turpin 1998).
|Habitat/ Ecosystem Type||Critical Load/ Level||Status||Reliability||Indication of exceedance||Reference|
|Arable and semi-natural ecosystems.||
400 mg/kg dry weight
|Environmental Assessment Level (Soil Quality Criteria)||quite reliable i.e. the results of some studies are comparable||
Soil Quality Criteria is a non-statutory Environmental Assessment Level. The corresponding maximum deposition rate was calculated to be 1.5 mg/m2/day.