برآورد غلظت زمينه‏اي عناصر كمياب سمي و اثر عمليات زراعي بر توزيع انباشت و بار آلودگي در خاك دشت بروجن- فرادمبه

Estimation of Baseline Concentration of Some Trace Elements and the Effect of Farming Practices on the Distribution of Accumulation and Pollution Loading Indices in the Soil of Boroujen-Faradonbeh Plain

غلظت كل سرب، كبالت، نیكل، كادمیوم، كروم و جیوه در خاك سطحی اراضی بایر، تحت كشاورزی مرسوم و تحت كاربرد پساب شهری اندازه‏گیری؛ و غلظت و حد زمینه‏ای، توزیع انباشت عناصر، و بار آلودگی تعیین شد. غلظت زمینه‏ای نیكل، كادمیوم، كرومیوم، جیوه، كبالت، سرب به ترتیب 13/1، 16/0، 56/1، 09/0، 80/0، و 52/1 و حد آن‏ها به ترتیب 3/1، 28/0، 6/1، 16/0، 9/0، و 7/1 میلی‏گرم بر گرم تعیین شد. كشاورزی مرسوم انباشت كادمیوم و سرب در خاك را به ترتیب به 7/1 و 9/1 افزایش داده (۵/۰ >p)، تمایل به افزایش كبالت، نیكل و جیوه‏ی از واحد به 2/1 خاك داشته ولی انباشت كروم را از واحد به 8/0 كاهش داده است (۵/۰

Introduction: Soil pollution, i.e. elevated concentration of undesirable organic and inorganic matter such as trace elements higher than natural background concentration can be a consequence of indirect or intentional human activities. Evaluation of the effect of the agricultural operations and particularly using the wastewater on soil trace element concentrations is useful and required to manage the land and reduce the health risks of the food products. The aims of this study were: [1] The estimation of the mean concentration and max limit of the background concentration for Cd, Cr, Ni, Pb, Co and Hg in the surface soil samples of Boroujen-Faradonbeh plain; and [2] Evaluation of the effect of agricultural operation and farming by non-conventional water on background concentration and on accumulation, distribution and pollution load of the soil of this plain. Materials and Methods: Boroujen-Faradonbeh is an agricultural plain loaced in the Chaharmahal and Bakhtiari mountainous province of Iran. Two hundered surface soil samples (0-20 cm) were taken from three types of land: never-uncultivated soil (20 samples), freshwater-irrigated (90 samples) and wastewater-irrigated (90 samples) soils. The total sampled area was about 2340 hectares. The exact position of the samples were recoded using a GPS device. The total concentrations of Pb, Co, Ni, Cd, Cr and Hg in the samples, and the background and upper limit concentrations were determined. In addition, pollution loading index (PLI) for the whole plain determined and delineated. To separate the affects of agricultural practices and wastewater application the analysis of variance of StatSoft Statistica 12 was used. Maping, and related operations were conducted inside ArcGIS 9.3. Results and Discussion: Background concentrations of Ni, Cd, Cr, Hg, Co, and Pb, were determined as 1.13, 0.16, 1.56, 0.09, 0.80, and 1.52 mg/kg, respectively; while upper limit concentrations for the mentioned trace elements were respectively 1.3, 0.28, 1.6, 0.16, 0.9, 1.7 mg/kg. Conventional farming (application of fertilizer but not wastewater) increased the soil accumulation factor of Cd and Pb to 1.7 and 1.9 (p <0.05), respectively, but reduced the accumulation factor of Cr from the unit to 0.8 (p <0.05). Wastewater application increased the accumulation factor of Ni and Cr (from 1.2 to 1.6 and from 0.8 to 1.2, respectively), and especially Pb and Co accumulation factor from 1.9 to 3.7 and from 1.2 to 1.9, respectively, while the accumulation factor of Cd was reduced from 1.7 to 1.3. About 8% of plain’s area, located in the western part where no wastewater is used, had a low pollution loading index between 0.85 and 1 while the remainder of the plain’s area, mostly located in the eastern part of the plain where both fertilizer and wastewater is applied, had a moderate pollution loading index of 1 to 2. The most polluted part of the plain with a loading index from 1.5 to 2 that covered 15% of the plain’s area was in the eastern part of the plain, where wastewater is most available. Overall, wastewater application in this area led to increase the accumulation factors and higher pollution loading indices. Howerver, the risks of conventional practices of fertilizer and pesticide use , though smaller, existed. Conclusions: In this study, about 92% of this plain was placed in the moderate pollution class (pollution load: 1 to :2). Most polluted farms were in eastern part of the plain where wastewater was used for irrigation. It is expected that the accumulation and pollution load of trace elements in this plain will exceed the current level given that the practice of using wastewater on the farms will not stop.. Soil pollution leads to the polluted meat and dairy products produced in the plain and the pollution of groundwater. In addition, wind dust in this plain contains toxin elements which is another concern. This points to detrimental effect of farming and wastewater application on soils. Current farming practices including the use of chemical fertilizers, pesticides and wastewater, coupled with increased population, will lead to more unfavorable conditions of trace metal pollution in the Boroujen-Faradonbeh plain.