Dust
Dust Impacts
Nuisance effects
Studies suggest that approximately one third of the dust emitted can escape from an open pit 453. Dust depositions on windows, on the outside of the house, and on cars are the most frequently mentioned reasons for concern. The problem can be worsened if deposition takes place on a surface which is normally expected to be free from dust, or if there is a nearby clean surface against which comparison can be made. A strong colour contrast or a general dirty appearance may also cause a strong reaction, although this can also be affected by people's expectations and other social factors.
The rate of deposition and therefore the time taken for dust deposition to become visible are important influences on the perception of dust. The rates of deposition vary widely with emissions, variations in wind speed and direction and also variations in the background dust concentration. These background levels will determine the reaction of local people to any additional dust from specific mineral sources, together with the factors in Table 5.
Table 5. Factors affecting the reaction of local people to dust.
| The frequency of dust deposition incidents | A community may be prepared to tolerate an incident once a month, but not repeated incidents at frequencies of one or two a week. |
| The amount of deposited dust | The amount of dust will usually decrease with distance, so the proximity to the source will be a major factor in the determining the level of complaint. |
| The area affected by deposition | If the emissions increase then there is the possibility of a larger area being affected. This will increase the probability of complaint unless the dust is diluted to a point below which people are concerned. |
One of the problems is how to quantitatively measure the rate and severity of soiling, as there is no agreed methodology and the alternatives all have various advantages and disadvantages. However, a number of methods are described later which can help to avoid dependence on subjective descriptions and complaints.
Health Effects
PM10 dust is associated with a range of effects on health including effects on the respiratory and cardiovascular systems, asthma and mortality. Detailed studies have been and continue to be made on the actual level of impact on health. Work published in 1999 by the University of Newcastle Department of Epidemiology and Public Health, investigated the impact of particulate matter from opencast workings on public health. It found that opencast coal mining was associated with a small increase in the mean concentration of airborne particles measured as PM10 in areas close to opencast sites, but that the respiratory health of children living in communities close to opencast sites was very similar to that of children living in communities distant from such sites. The increase in particulate concentration close to the opencast sites was mainly due to earth moving and excavation, rather than any coal particles.
It is not thought that there are any substantiated claims that health has been affected around working quarries.
Historic environment
An ALSF project L0295 has considered the effects of dust on historic environments, through soiling or chemical reactions between certain mineral dusts (e.g. limestone) and building materials. In two historic villages in close proximity to large aggregates workings, fresh quarry dust was found inside all the houses that were investigated, up to distances of almost 1km from the quarry perimeters. This is potentially abrasive to delicate surfaces and finishes and could have implications for the maintenance of historic street materials such as delicate lead-work and old glass where it is not readily washed off by rain.
As historic buildings near limestone quarries are often constructed of the local stone, dust from the quarry is likely to be chemically similar and so unlikely to react with such outdoor masonry.
Dust concentrations due to quarry traffic to and from the site are likely to be lower than in the past, due to mitigation measures such as sheeting and wheel-washing.
Ecology and agriculture
There are few detailed studies of the effects of dust deposition on ecology and agriculture. Dust may have physical effects on plants such as blockage and damage to stomata, shading, abrasion of leaf surface or cuticle, and cumulative effects e.g. drought stress on already stressed species.
The chemical effects of dust, either directly on the plant surface or on the soil, are likely to be more important than any physical effects. Dust deposited on the ground may produce changes in soil chemistry, which may in the longer-term result in changes in plant chemistry, species competition and community structure. However, the soil type surrounding a mineral site will probably reflect the mineral being worked, so this is unlikely to be a common problem.
Many rock materials such as chalk and limestone have traditionally been used in agriculture to increase crop sensitivity. Dust deposition levels are likely to be well below the level of agricultural applications, and therefore effects on agricultural crops are likely to be minimal. Areas of high ecological value (designated nature conservation areas) or agricultural resources (intensive horticultural areas and fruit growing areas) may be more sensitive to dusts than other areas.
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