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).
Key concerns:
Boron toxicity in plants is most likely to occur following the continued use of boron-contaminated irrigation waters, however, direct exposure from airborne emissions may also produce localized toxic effects (Howe 1998). Symptoms of boron toxicity in plants include yellowing, spotting or drying of leaf tissues, especially on the tips and sides of older leaves (Gupta et al. 1985).
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Concentrations of arsenic in soil reported to be toxic to plants span a broad range (WHO 2001), and toxicity is generally higher in sandy soils than clay soils (Sheppard 1992).
Additional Comments:
Key Concerns:
There is a paucity of data on the effects of antimony on species and their ecosystems.
Emissions of antimony, such as those from smelters, can remain in the atmosphere for more than one month and therefore be transported over long distances (ATSDR 1992; Steinnes 1997). Antimony in soil is likely to be in the form of antimony sulphide, which is slightly soluble, and therefore potentially bioavailable.
Key concerns:
There is a paucity of data on the effects of PAHs on species indicative many terrestrial ecosystems. Some PAHs are known or suspected carcinogens, although the ecological consequences have not been established, as most organisms will be predated before they develop carcinomas. However tumours in fish can present a problem for the human food chain.
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Soot, like particles in general, may affect vegetation by both physical and chemical processes. Physically, pa rticles may cover the leaf surface and reduce the amount of light available for photosynthesis, or may occlude stomata. Occlusion may lead to increased resistance to gas exchange, or may prevent full stomatal closure, leading to water stress. Increased transpiration is a common response to particle exposure. Infestation by pests and pathogens is likely to be enhanced.
Key Concerns: Quarry dusts, like dusts in general, affect vegetation by both physical and chemical processes. Physically, dust may cover the leaf surface and reduce the amount of light available for photosynthesis, or may occlude stomata. Occlusion may lead to increased resistance to gas exchange, or may prevent full stomatal closure, leading to water stress. Increased transpiration is a common response to dust exposure.
Key Concerns:
The term 'particulates' includes a range of chemically and physically different material in sizes ranging from a few nanometres (millionths of a millimetre) in diameter, up to a few tens of micrometres (thousandths of a millimetre)in diameter. Smaller particles are transported through the atmosphere by turbulence. Larger particles may be suspended from the ground by the wind, and then settle under the force of gravity.
