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.
Chemically, cement dusts are strongly alkaline, and may have detrimental effects on leaf surfaces. Infestation by pests and pathogens is likely to be enhanced.
Trees and woodlands receive greater deposition of dust than adjacent short vegetation because of increased air turbulence. In extreme cases, dust deposition may lead to tree death, but less severe symptoms are changes in pigments, sugars, and overall growth, detectable over a few km from a major source (Mandre et al., 1999).
Indirect effects may be caused through the soil, especially on acid soils, where the cement dust can increase the pH and available calcium, leading to changes in vegetation composition. The subject has been reviewed in depth by Farmer (1993).
Effects of cement dust have been observed for deposition rates as low as 0.5 g/m2/day. Often, deposition rates are not measured, and exposure is judged by amounts retained on leaves. However, removal of dust from leaves by rain varies very greatly among plant species, from those that are 'self-cleaning' (the lotus effect) to those that accumulate large quantities. Most industrial processes are regulated to prevent emission of cement dust.
|Habitat/ Ecosystem Type||Eunis Code||Critical Load/ Level||Status||Reliability||Indication of exceedance||Reference|
|All ecosystems (except freshwater)||n/a||
No defined value
|n/a||insufficient data i.e. insufficient data to provide estimate||
No critical loads have been defined. Exposure is rarely measured in terms of deposition rates, but as the amount of dust retained on plant surfaces. Effects have been detected at deposition rates of 0.5 g/m2/day