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.
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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.
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Fly ash is produced when pulverised fuels are burnt. Like other types of dust, fly ash may affect vegetation by both physical and chemical processes. Physically, particles 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. Deposition rates to tall vegetation are greater than to short vegetation.
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Cement 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.
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Short-chain alcohols and aldehydes are produced and emitted by some plants. There is evidence that methanol applied to leaves may be beneficially metabolised. Biochemical pathways exist in plants to regulate formaldehyde concentrations, and experiments with trees have suggested that many species are tolerant of high concentrations (microlitre/litre or ppm) on short-term (hours) exposure. See review by Cape(2003).
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There is almost no information on the effects of volatile organic compounds (VOCs) on vegetation at concentrations likely to be experienced even in polluted urban air, or over timescales longer than a few hours. The literature has been reviewed (Cape, 2003; Collins & Bell, 2002).
Benzene may accumulate in the leaves and fruit of some species, but is unlikely to be of concern at concentrations typical of rural air (Collins et al., 2000).
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Hydrogen fluoride (HF) is the most phytotoxic of all air pollutants. It accumulates in the margins and tips of leaves, and in sensitive taxa it causes:
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