EFFECT OF AIR POLLUTION ON FOOD SECURITY (AGRICULTURAL PRODUCTS)

INTRODUCTION.

Agricultural crops can be injured when exposed to high concentrations of various air pollutants. Injury ranges from visible markings on the foliage, to reduced growth and yield, to premature death of the plant. The development and severity of the injury depends not only on the concentration of the particular pollutant, but also on a number of other factors. These include the length of exposure to the pollutant, the plant species and its stage of development as well as the environmental factors conducive to a build-up of the pollutant and to the preconditioning of the plant, which make it either susceptible or resistant to injury.

EFFECTS OF AIR POLLUTION ON PLANTS GROWTH

Air pollution injury to plants can be evident in several ways. Injury to foliage may be visible in a short time and appear as necrotic lesions (dead tissue), or it can develop slowly as a yellowing or chlorosis of the leaf. There may be a reduction in growth of various portions of a plant. Plants may be killed outright, but they usually do not succumb until they have suffered recurrent injury.

TYPES OF AIR POLLUTANTS THAT AFFECT PLANT GROWTH.

OXIDANTS. 

Ozone and Nitrogen dioxide are the main pollutants in the oxidant smog complex. Its effect on plants was first observed in the Los Angeles area in 1944. Since then, ozone injury to vegetation has been reported and documented in many areas throughout North America, Africa, Asia and recently Europe.

Throughout the growing season, particularly July and August, ozone levels vary significantly. Periods of high ozone are associated with regional  air flows that are carried across after passing over many urban and industrialized areas. Localized, domestic ozone levels also contribute to the already high background levels. Injury levels vary annually and white beans, which are particularly sensitive, are often used as an indicator of damage. Other sensitive species include cucumber, grape, green bean, lettuce, onion, potato, radish, rutabagas, spinach, sweet corn, tobacco and tomato. Resistant species include endive, pear and apricot. The main effect of these oxidant pollutants they block and affect chlorophyll pigments from sunlight trapping hence affect the overall photosynthesis process.

SULFUR DIOXIDE.

Major sources of sulfur dioxide are coal-burning operations, especially those providing electric power and space heating. Sulfur dioxide emissions can also result from the burning of petroleum and the smelting of sulfur containing ores.

Sulfur dioxide enters the leaves mainly through the stomata (microscopic openings) and the resultant injury is classified as either acute or chronic.

Acute sulfur dioxide injury to raspberries. Note that the injury occurs between the veins and that the tissue nearest the vein remains healthy due to interference in plant nervous system

FLUORIDES

Fluorides are discharged into the atmosphere from the combustion of coal; the production of brick, tile, enamel frit, ceramics, and glass; the manufacture of aluminum and steel; and the production of hydrofluoric acid, phosphate chemicals and fertilizers.

Fluorides absorbed by leaves are conducted towards the margins of broad leaves (grapes) and to the tips of monocotyledonous leaves (gladiolus).

Fluoride injury to plum foliage. The fluoride enters the leaf through the stomata and is moved to the margins where it accumulates and causes tissue injury. 

Note the characteristic dark band separating the healthy (green) and injured (brown) tissues of affected leaves.

AMMONIA

Ammonia injury to vegetation has been observed frequently in the world in recent years following accidents involving the storage, transportation or application of anhydrous and aqua ammonia fertilizers. These episodes usually release large quantities of ammonia into the atmosphere for brief periods of time and cause severe injury to vegetation in the immediate vicinity.

Sensitive species include apple, barley, beans, clover, radish, raspberry and soybean. Resistant species include alfalfa, beet, carrot, corn, cucumber, eggplant, onion, peach, rhubarb and tomato.

Severe ammonia injury to apple foliage and subsequent recovery through the production of new leaves following the fumigation

PARTICULATE MATTERS.

Particulate matter such as cement dust, magnesium-lime dust and carbon soot deposited on vegetation can inhibit the normal respiration and photosynthesis mechanisms within the leaf. Cement dust may cause chlorosis and death of leaf tissue by the combination of a thick crust and alkaline toxicity produced in wet weather. The dust coating (Fig. 5) also may affect the normal action of pesticides and other agricultural chemicals applied as sprays to foliage. In addition, accumulation of alkaline dusts in the soil can increase soil pH to levels adverse to crop growth.

CONCLUSION. 

Generally, air pollution has a severe effect on plant growth and mainly affects food agricultural commodities. The whole world is fighting against hunger (SDG 2). We are also required to focus on how to prevent air pollution so as to enhance food security in the whole world.