Air pollution impacts to agricultural crops

Although air pollution levels are increasing, there is no knowledge of air pollution effects on agricultural crops in the Peshawar region of Pakistan. The aim of this study was to assess the impact of ozone (O3) and hydrogen fluoride (HF) on agricultural crops in Peshawar through a combination of field work and experiments. The mean monthly O3 concentration in Peshawar, measured using passive samplers, was between 25-30ppb in February and March, but increased to 35-55ppb in April and May; it fell to 15-20ppb in November/December. O3 injury was found on potato (black flecking), onion (leaf tipburn) and cotton (white stipples) in a survey in April/May, but was absent from many other crops. No O3 injury was found on any crops during a winter survey. O3 fumigation experiments on spinach (Beta vulgaris) and onion (Allium cepa) in open-top chambers in UK showed that high O3 concentrations can affect both species in terms of visible injury and growth. However, onion is at greater risk in the field as it is a summer crop and is likely to be exposed to high O3 concentrations, unlike spinach, which is grown in the winter season. An EDU experiment on spinach under field conditions in Peshawar showed no effect on growth during winter season. However, elemental contents of spinach were significantly reduced in EDU treated plants. The HF concentrations in Peshawar, measured using passive samplers were higher in summer than in winter in areas close to brick kiln fields. The mean summer concentration was 0.2μg HF m-3, with maximum of 0.3μg HF m-3 in May. HF was below detection limits of <0.1μg HF m-3 in November-December. Severe HF injuries to mango, apricot and plum leaves, in form of necrotic leaf margins and tipburn, were found near the brick kiln fields. Tomato, maize, wheat and sugarcane were found to be less sensitive, but also showed some HF injury. The fluoride content of fruit leaves, wheat grains and spinach was significantly higher in the brick kiln area than at control sites. There was no significant difference between the soil fluoride content of wheat fields in the brick kiln area and at control sites. Wheat grown at different NaF levels in alkaline soils similar to those in Peshawar, in a greenhouse experiment in the UK showed no effect of fluoride on growth. The degree of powdery mildew infestation increased with increased fluoride concentrations in the soil and ear emergence was also delayed in all treatments except the control. It was concluded that O3 and HF are significant pollutants in Peshawar, especially for summer crops. More detailed studies should be conducted to determine the magnitude of damage caused by these pollutants in the Peshawar region.