Platinum group :: all ecosystems

Key Concerns

There is a paucity of data regarding effects of airborne platinum group metals on ecosystems. However toxic effects, including inhibited transpiration, and histopathology have been reported in plants exposed to high concentrations of either platinum or palladium salts following exposure in a nutrient solution (WHO 1991; WHO 2002). 

Arable habitats - phytotoxicity, as evident by stunted roots and growth retardation has also been reported in various crop species, including barley, wheat, oats, peas and beans, exposed to soluble platinum group metal salts in a nutrient solution. Oats were the most sensitive species, with effects evident following exposure to 0.132 mg Pd / litre (Brenchley 1934). Reduced growth of radish, cauliflower, snapbean, sweetcorn, pea, tomato, bell pepper, broccoli and turnips was reported following exposure to 5.7 mg Pt / litre (Pallas and Jones 1978).

Coastal and rocky habitat – platinum group metals present in the aquatic environment as a result of run-off from roads, have been shown to be bioavailable to various species of marine algae (Hodge et al. 1986) and macrophytes (Yang 1989).

Freshwater – platinum group metals present in the aquatic environment as a result of run-off from roads, have been shown to be bioavailable to various species of freshwater organisms, including water hyacinth (Eichhornia crassipes) (Farago and Parsons 1994), oligochaete worms (Lumbriculus varieegatus) (Veltz et al. 1996) and zebra mussels (Dreissena polymorpha) (Zimmermann et al. 2002).

Grassland – toxic effects, including inhibited transpiration, and histopathology have been reported in plants exposed to high concentrations of either platinum or palladium salts following exposure in a nutrient solution (WHO 1991; WHO 2002). Death of Kentucky bluegrass (Poa pratensis) plants occurred within 1 week of exposure to 60 mg Pd / litre, or within 2 days following exposure to 300 mg Pd / litre. Transpiration was inhibited at 6 mg/l, with histopathological effects, including aberrant stomatal histogenesis, inhibited nodal meristem development, hypertrophy of mesophyll cells and changes in chloroplast structure, reported at 1.8 mg/l (Benedict 1970; Sarwar et al. 1970). Phytotoxicity, as evident by stunted root growth and chlorosis of the leaves was reported in another grass species (Setaria verticillata) exposed to platinum solutions, with concentrations greater than 2.5 mg Pt / litre (Farago and Parsons 1986).

Woodland and hedgerow – toxic effects, including inhibited transpiration, and histopathol ogy have been reported in plants exposed to high concentrations of either platinum or palladium salts following exposure in a nutrient solution (WHO 1991; WHO 2002). Platinum concentrations in twigs from limber pines (Pinus flexilis) growing near a platinum mining area ranged from 12 to 56 µg/kg ash. Concentrations in the twigs were similar to those found in soil (Hodge et al. 1986). Palladium has also been found in various species of tree, including Californian black walnut (Juglans hindsii), white oak (Quercus lobata), red pine (Pinus resinosa), manzanita (Arctostaphylos nummularia) and live oak (Quercus chrysolepsis) at concentrations at least two times higher than those found in corresponding soil samples (Kothny 1979).

Additional Comments

Platinum group metals are released to the atmosphere from industrial sources, and from vehicles fitted with catalytic converters. Emissions are generally in the form of either the metal, or its oxides, and they generally have limited bioavailability. Palladium has been found in a number of plants, suggesting greater mobility in the environment, and subsequent bioavailability, than platinum. The mobility of platinum group metals in soil depends on the characteristics of the soil, including its pH, redox potential, the concentration of chloride in soil water, and the mode of occurrence of platinum in the primary rock (WHO 1991; WHO 2002).