Exposure assessment of nitrate and phenol derivatives in Tehran's water distribution system.

The presence of organic and inorganic contaminants in drinking water is a global concern. Nitrate and phenol derivatives are examples of pollutants that could be of anthropogenic origin. They are associated with numerous health risks, underscoring the importance of monitoring their presence in drinking water. This study aimed to measure nitrate and phenol derivatives, including 2,4-Dichlorophenol (2,4-DCP), Pentachlorophenol (PCP), 2,4,5-Trichlorophenol (2,4,5-TCP), 2-Chlorophenol (2-CP), 4-Chlorophenol (4-CP), and phenol, in Tehran's water distribution system (WDS). The pollutants in Tehran's WDS were significantly and positively correlated with precipitation. The Hazard Quotient (HQ) and the Excess Lifetime Cancer Risk (ELCR) of the detected pollutants were estimated. The results showed that the regional mean of nitrate and PCP in Tehran's WDS were 35.58±8.71mg L-1 and 76.14±16.93 ng L-1 lower than the guideline values of 50 mg L-1 and 1000 ng L-1, respectively. Some districts exhibited nitrate concentration exceeding the allowable limit by a factor of 1.2 to 2.3. Consequently, the nitrate intake in some districts constituted approximately 50% of the reference dose. While PCP as a phenol derivative with more health concerns was identified in Tehran's WDS, the likelihood of its health effects was determined to be negligible.

Presence of heavy metals in drinking water resources of Iran: a systematic review and meta-analysis.

Water quality is one of the most important indices for public health especially for drinking water consumptions. This study was conducted to survey the presence of heavy metals in drinking water resources of Iran using a systematic review and meta-analysis. The literature search was conducted in data bases of PubMed, Web of Science, EMBASE, Scopus, Google Scholar, and some Persian databases up to 31 July 2018. Of all the articles reviewed (1151 articles), 61 papers were eligible for systematic review. Results indicated variable heterogeneity between studies for different pollutants (I2 between 0 and 100). A subgroup analysis was performed for three different types of water resources such as drinking water, groundwater, and surface water to find the possible source of the heterogeneity. The pooled mean concentration level of iron was the highest at 255.8 (95% CI = 79.48-432.13 µg/l) and vanadium the lowest at 3.21 (95% CI = 1.45-4.98 µg/l). The sequence of metal concentration (µg/l) in descending order is as follows: Fe (255.8) > B (159.81) > Al (158.5) > Zn (130.73) > As (85.85) > Mn (51.61) > Cu (47.98) > Se (42.68) > Pb (37.22) > Co (22.76) > Mo (18.92) > Ni (16.79) > Cr (13.47) > Hg (4.49) > Cd (4.19) > V (3.21). The mean pooled concentration level of Al, As, Se, Pb, and Cd was higher than the WHO guideline and Iran Standard, and the rest of the metals had lower mean pooled concentration level. Pb and Cd were the common heavy metals that existed in all subgroups. As a recommendation, the relationship assessment of water parameters and heavy metals could be addressed in future studies of Iran's water resources.

Acute toxicity of Hg, Cd, and Pb towards dominant bacterial strains of sequencing batch reactor (SBR).

One of the most important factors that affect the operation efficiency of sequencing batch reactor (SBR) technology is bacterial viability and biomass activity. The acute toxicity of three heavy metals to four dominant strains of sequencing batch reactor (Pseudomonas, Aeromonas, Enterobacter, and Bacillus) was investigated using a resazurin bioassay. After exposing the bacterial strains to soluble compound of Hg, Cd, and Pb, at more than five selected concentrations, the median effective concentration (EC50) and the mortality rate values were calculated. Large differences were observed in sensitivities of the four bacterial strains to the metals. Pseudomonas showed the highest sensitivity for Cd (EC50 = 0.06 µmol/L) and Hg (EC50 = 11.75 µmol/L), while Aeromonas showed the highest sensitivity for Pb (EC50 = 48.27 µmol/L). Considering the EC50 test results, it was concluded that Pseudomonas and Aeromonas are excellent and reliable bioindicators for assessing the toxicity of water and wastewaters polluted by Cd, Hg, and Pb. The rapidity (30 min) and simplicity of the resazurin bioassay procedure enable this enzymatic test to be used in toxicity assessment of small and decentralized wastewater treatment plants (WWTPs).

Investigation of photocatalytic degradation of phenol by Fe(III)-doped TiO2 and TiO2 nanoparticles.

In this study Fe (III)-doped TiO2 nanoparticles were synthesized by sol-gel method at two atomic ratio of Fe/Ti, 0.006 and 0.034 percent. Then the photoactivity of them was investigated on degradation of phenol under UV (<380 nm) irradiation and visible light (>380 nm). Results showed that at appropriate atomic ratio of Fe to Ti (% 0.034) photoactivity of Fe(III)-doped TiO2 nanoparticles increased. In addition, the effects of various operational parameters on photocatalytic degradation, such as pH, initial concentration of phenol and amount of photocatalyst were examined and optimized. At all different initial concentration, highest degradation efficiency occurred at pH = 3 and 0.5 g/L Fe(III)-doped TiO2 dosage. With increase in initial concentration of phenol, photocatalytic degradation efficiency decreased. Photoactivity of Fe (III)-doped TiO2 under UV irradiation and visible light at optimal condition (pH = 3 and catalyst dosage = and 0.5 g/L) was compared with P25 TiO2 nanoparticles. Results showed that photoactivity of Fe(III)-doped TiO2 under visible light was more than P25 TiO2 photoactivity, but it was less than P25 TiO2 photoactivity under UV irradiation. Also efficiency of UV irradiation alone and amount of phenol adsorption on Fe(III)-doped TiO2 at dark condition was investigated.