Impact of rapid urbanization on the surface water's quality: a long-term environmental and physicochemical investigation of Tajan river, Iran (2007-2017).

Sustainable development of our society requires protection and monitoring of aquatic environments, as they are the pivotal water resources and niche for wildlife animals. In this research, physicochemical parameters of Tajan river's water were determined and compared with standards to assess the rural and human activity impact on water quality. First, monitoring and analyzing the water quality of the river were performed for 11 years (from 2007 to 2017). Based on calculated water quality index (WQI) values, Tajan river's water quality falls into four categories: good water with WQI less than 30 at upstream and middle of the river, poor water, and very poor to even unsuitable water (WQI ranges from 86 to 134) at the more urbanized locations. The high values of WQI are due to an elevated concentration of sulfate, nitrate, total dissolved solids (TDS), and chloride substances. The source of contaminations, according to the geochemistry of the area and having more than 90% growth rate in the population near to the most polluted location, is probably anthropogenic activities. Then, the long-term experimental data set has been utilized for developing a statistical model to be used for prediction of water quality with a few chemical analyses, generating a rapid and low-cost water quality evaluation for this river. The model was developed based on the stepwise multiple linear regression (MLR) approach and confirmed the experimental observation data of the most defective elements on WQI were respectively SO4, NO3, TDS, Cl, pH, and EC. This study presents a long-term evaluation of changes in surface water quality at a region with a recent rapid urban and civil development providing a suitable case to understand better human-water relations.

The high levels of heavy metal accumulation in cultivated rice from the Tajan river basin: Health and ecological risk assessment.

Consumption of food crops contaminated with heavy metals (HMs) is a significant risk factor for human health and safety. We evaluated the health risks of HMs in contaminated food crops irrigated with surface water. Results showed there is a substantial buildup of HMs in rice, collected from the Tajan river basin, Iran. The transfer factor (TF) value for toxic elements Cd (3.6-12.4) and Pb (4.9-23.6) were significantly high and exceeded the permissible limits for crops set by WHO. The principal component analysis was used to analyze the relevance of different metals and identify the primary sources. The results showed that two factors dominated the metals variability (94.10% of total variance) that Cr, Fe, Cd, and Pb were dominated by PC1 whereas another factor charged Zn and Cu. The average total hazard quotient (THQ) values for Pb, Fe, Cr, and Cd were 13.8, 7.7, 5.5, and 1.5, respectively, that suggest a considerable risk to the health of regular rice consumers. The high hazard index (HI) value (29.2) demonstrated that the exposure concentration was very high compared to the effective threshold, and it may have potentially harmful implications for human health. To sum up, these results proved that rice from this basin could be a serious dietary source of Pb and Cd exposure to the consumer population.