عنوان مقاله [English]
Heavy metals in dust particles play an important role in contamination of agricultural soils, being one of the most dangerous pollutants in the environment due to their bioaccumulation power. In other words, they are able to accumulate inside the bodies of living organisms and increase their concentration with greater exposure to pollutants. Heavy metals are generally referred to as a group of elements with a specific gravity, greater than 6 g/cm3, more than 50 g of atomic weight. The most important heavy metals, important for environmental protection, include cadmium, arsenic, cobalt, vanadium, zinc, mercury, iron, manganese, nickel, lead, chromium, and copper which owing to their non-biodegradability in the nature as well as long life span, are considered important pollutants in the environment. Moreover, pollution of agricultural lands with metals through chemical activities like sewage sludge, chemical fertilizers, and industrial wastewater along with the deposition of dry and wet dust particles from dust storm phenomenon can be seen as one of the most important sources of pollutants for wheat agronomic ecosystems to heavy metals. Pollution with heavy metals from dust storms is considered a serious problem due to toxicity, degradability, and cumulatively. Following the deposition of dust particles, contaminated with heavy metals on crop fields, the contaminants are combined with the soil solution. As the plants absorb the heavy metals in this way, they pave the road for them to get transferred to the food chain. As a result, deposition of dust particles with heavy metals in the soil of wheat agro ecosystems can endanger human health and the present research aims at identifying the heavy metals content in wheat fields, which is the first step to reduce this health risk.
Materials and Methods
This study obtained the data concerning the dust storms in a 16-year period (2000-2015), belonging to Larestan, Jahrom, Darab, and Fasa Stations, from the Meteorological Organization. It then analyzed the frequency of dust storms on both a seasonal and an annual scale. Next, the dust particle entry pathway to the study area on May 12, 2018 was performed, using HYSPLIT model. This was followed by obtaining soil samples from wheat farms in Larestan, Fasa, Darab, and Jahrom. Four wheat ecosystems got identified in each study area and soil sampling was performed from a depth of 1 cm at an area of 400 cm2 in each ecosystem. The soil sampling was divided into two stages: before and after the dust storm. Pre-dust storm sampling took place in December and March, and post-dust storm one happened in May and June. Soil samples were transferred to the laboratory, where their concentration of lead, cadmium, and nickel was measured via flame atomic absorption spectrometry. Finally, the amounts of heavy metals in the soil samples were evaluated by the Igeo index.
Results and Discussion
The maximum frequency of dust storms in the southern part of Fars Province is due in warm months, especially in the spring, with an average of 18 dust storms per season. The minimum occurrence rate of this environmental phenomenon belongs to the cold months, especially in the autumn, which occurs less than once a season. In addition, among the stations in the study area, Fasa Station usually faces the maximum annual dust storms with 42 occurrences, with Jahrom, Darab, and Lar Stations in the next ranks with 39, 25, and 19 storms per year, respectively. The path of dust particles entering the study area on May 12, 2018 was tracked, using HYSPLIT Model in a backward method. The results showed that deployment of thermal low-pressure in the Persian Gulf had destabilized the atmosphere and Shamal winds moved through the deserts of Iraq and Saudi Arabia to the Persian Gulf, both contributing to the transportation of a massive amount of dust particles into the southern provinces of Iran. Moreover, the results showed that concentrations of lead and cadmium in the soil of wheat agronomic ecosystems of Fars Province increased under the influence of dust storms, whereas the concentration of nickel remained unchanged. The highest concentrations of heavy metals were in Darab and Lar ecosystems and the lowest in Jahrom and Fasa. The mean comparison test showed a significant difference between the concentrations of heavy metals in agricultural ecosystems in southern Fars province before and after the dust storm at 0.05 and 0.01 levels. Also, dust storms increased the heavy metals in the soil of wheat ecosystem. Furthermore, the land pollution standard showed that in the agricultural wheat ecosystems of Darab, the concentration of all metals was higher than the global limit, being in the moderate to severe pollution category.
This study investigated the effect of desert dust on heavy metal concentration in soil ecosystems, measuring their concentrations before and after the occurrence of dust and comparing their differences with statistical tests. It showed that the concentration of lead and cadmium in the soil of wheat agronomic ecosystems increased under the influence of dust storms, while that of nickel remained unchanged.
In addition to combustion sources, industries and factories, traffic, and the use of fertilizers and municipal wastewater, desert dust particles contribute to air pollution, too. Higher concentrations of heavy metals in agricultural soil can affect health and damage environmental ecosystems and organisms, especially humans, the chief consumers of these agricultural soil products. Deposition of dust particles, caused by dust storms in cultivated wheat soils, results in increased concentrations of heavy metals in the soil and its uptake by plant roots and movement to the crops put human health in jeopardy. Because wheat is one of the most consumed morsels in human diet and given that movement of toxic substances as well as heavy metals through soil, roots, and plants causes them to accumulate in wheat, in order to achieve world-class quality and health products, some solutions must be offered to reduce heavy metal concentrations in consumer products. Thus, this study’s results could and should be made available to not only planners but also agricultural and health experts.