Groundwater quality in bone-dry and semiarid areas of Iran is decreasing because of contaminants from natural origins and anthropogenic sources. Among many harmful contaminants, nitrate and fluoride ions are more common. This study was carried out with the aim of determining geochemical processes controlling chemistry of groundwater with special reference to nitrate and fluoride enrichment in groundwater in Lar plain aquifer, south of Iran. Groundwater samples were collected from 17 sites and analyzed for main constituents (Na, K, Ca, Mg, Cl, SO, HCO, F, and NO). Composite diagram, saturation indices calculation, and multivariate analysis techniques including cluster and factor analyses were employed in evaluating groundwater quality. The EC ranges from 8793.87 to 13,345.00 μS/cm in wet season and from 9621.59 to 12,640.00 μS/cm in dry season. Fluoride amounts range between 0.59 and 3.92 mg/L. Nitrate concentrations range between 1.47 and 70.66 mg/L. Results indicate that dissolution-precipitation of carbonate and evaporate minerals, evaporation (in terms of agricultural water return), and opposite ion interchange are the main processes that determine groundwater chemistry. It seems that fluoride has a natural origin and the equilibrium reaction between fluorite and calcite is very significant to control fluoride concentration level in water. Vertical variation of nitrate concentration and distribution of agricultural areas have indicated that nitrate originated from nitrogenous inorganic fertilizers used during irrigation periods. The results also indicate that denitrification takes place in the aquifer and that nitrate decline is not only a function of dilution but also a process of denitrification.

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The purpose of this study was to assess selected potentially toxic elements and persistent organic pollutants concentrations in the Shahid Rajaei Dam reservoir as well as their accumulation in barbel and Leuciscus cephalus fish species. The concentration of arsenic, mercury, nickel, chromium and cadmium in all water samples is less than WHO drinking water standard. Chromium shows a higher concentration than WHO standard in both fish species, while nickel and mercury content in barbel fish is higher than WHO standard. The result of principle component analyses indicates an increased elemental concentration due to application of phosphorus fertilizers in the agricultural lands, especially paddy field, ending up to the Tajan River and Shahid Rajaei Dam reservoir. Ni, Co, Mn, Pb and Cr display a quasi-independent behavior within the groups (PC1, PC2 and PC3) reflecting contribution of both geogenic and anthropogenic sources. The concentrations of persistent organic pollutants in all water samples, except M-5 sample, are less than WHO and EPA drinking water standards, while persistent organic pollutants (detected in both fish species) indicate higher contents than those of EPA standard values. Based on carcinogenic health risk value, maximum allowable fish consumption for arsenic is two meals per month. The result of noncarcinogenic health risk of mercury indicates one and three meals consumption per month for barbel and L. cephalus fishes, respectively. The calculation of maximum allowable fish consumption based on carcinogenic health for dieldrin, P HCH, heptachlor epoxide, P DDT and P PCBs reveals monthly meals limitation of both fish species grown in Shahid Rajaei Dam.

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