Cadmium :: terrestrial ecosystems

Key concerns

Cadmium has been shown reduce the growth of plants. Most of the data are from laboratory studies, in which plants were exposed to nutrient solutions containing soluble cadmium salts in the mg/l concentration range. Cadmium found in the environment is likely to be bound to soil and is subsequently less bioavailable (Eisler 1985; WHO 1992).

Arable habitats -  various arable plant species, including maize (Ramachandran and D'Souza 2002), spring wheat (Triticum aestivum) (Nan et al. 2002) and romaine lettuce (Brown et al. 1998), have been shown to adsorb cadmium from soil, especially under acidic conditions. Arable crops may also adsorb cadmium from the atmosphere, with atmospheric adsorption accounting for 10 to 60% of cadmium taken up by crops (Smolders 2001). Soil cadmium concentrations ranging from 7.5 to 22.5 mg Cd / kg soil have been shown to inhibit the growth of triticale and oilseed rape (Ciecko et al. 2001).

Bogs, wetland and heath - some wetland species, such as water hyacinth (Eichhornia crassipes) and duckweed (Limna minor) can accumulate high concentrations of cadmium; 462 and 14200 mg/kg, respectively (Wang et al. 2002). Cadmium concentrations in water hyacinth roots (6103 mg/kg dw) were significantly higher than corresponding concentrations in t he shoots (371 mg/kg dw) (Zhu et al. 1999).

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 - cadmium concentrations in calcareous soils are correlated with carbonate con tent (Sanchez-Camazano et al. 1998). Uptake of cadmium by grassland plants such as Salix viminalis and Thlaspi caerulescens was far greater in acidic soil, compared to calcareous soil (Hammer and Keller 2002). Most of the cadmium taken up by the plants in acid soil was bound to organic matter, whereas in the calcarious soil, it was bound to carbonate. Increased cadmium concentrations have been reported in grass (Lolium species) sampled from sites close to roads (Garcia and Millan 1998). Cadmium concentrations in the grasses ranged from ND to 0.82 mg/kg, and unlike the underlying soil concentrations, were not significantly correlated with sampling site or distance from the road.

Woodland and hedgerow – cadmium has been shown to reduce the growth of both foliage and roots of various species of tree seedlings following exposure to solutions ranging from 0.5 to 64 µg Cd/l (Mitchell and Fretz 1977). Effects reported include interveinal chlorosis and stunting of the leaf, followed by wilting and plant death, in red maple (Acer rubrum), inhibition of needle expansion in white pine (Pinus strobes) and chlorotic tips to the new growth of Norway spruce (Picea abies). In all species tested, cadmium accumulated was greater in the roots than the leaves. No effect on growth, as measured by shoot biomass, root biomass, total root length and total root tip density was reported for Scots Pine (Pinus sylvestris) seedlings growing in soil cadmium concentrations up to 200 mg/kg dry weight (Hartley-Whitaker et al. 2000). However, cadmium concentrations greater than 20 mg/kg were found to inhibit colonization of the seedlings by ectomycorrhizal fungi. Inhibition of ectomycorrhizal fungi may have serious implications for successful tree establishment in cadmium-contaminated soils.