en Environmental Health, Sciences, and Engineering Original articles <div style="text-align: justify;"><span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><i><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Introduction:</span></span></span></i></b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times=""> Contamination of water sources with toxins is an environmental problem and a serious threat to the health of societies<a name="_Hlk152400301">. This study aimed to ascertain the remaining levels of toxins in urban drinking water networks and compute the water quality index.</a><a name="_Hlk151972623"> </a></span></span></span></span></span></span><br> <span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><i><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Materials and Methods:</span></span></span></i></b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times=""> To examine the residual concentration of </span></span></span><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">diazinon</span></span></span><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">, chlorpyrifos, and dichlorvos in urban drinking water distribution networks, 35 underground and surface water sources were sampled in Tiran-o-Karvan </span></span></span><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">in Isfahan province, Iran</span></span></span><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">. GC-ECD device was used to analyze the samples.</span></span></span></span></span></span><br> <span style="font-size:11pt"><span style="line-height:115%"><span calibri="" style="font-family:"><b><i><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">Results:</span></span></span></i></b><span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times=""> Diazinon was not observed in any of the sampling seasons.</span></span></span> <span style="font-size:10.0pt"><span style="line-height:115%"><span new="" roman="" style="font-family:" times="">The maximum concentration of chlorpyrifos and dichlorvos was 61 and 100 ppb, respectively. Although chlorpyrifos was seen more in the hot season and dichlorvos in the cold season, the mean concentration of these toxins in different seasons was lower than the guidelines of Iran and the World Health Organization (WHO). The mean concentration of nitrate, and hardness, in wet and dry seasons was 46.23 and 46.42, and 343.7 and 338.8 mg/l, respectively.</span></span></span></span></span></span><br> <b><i><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">Conclusion:</span></span></span></i></b> <span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">The mean and standard deviation of quality index of Iran&#39;s water resources (IRWQI) in wet and dry seasons were 52.16 &plusmn; 45.3 and 50.69 &plusmn; 15.8, respectively. The residual concentration of toxins in some water sources of this city exceeded the guidelines of Iran and the WHO in summer and spring.</span></span></span></div> Diazinon, Chlorpyrifos, Dichlorvos, Drinking Water, IRWQI,Tiran-Karvan City. 2149 2158 http://jehsd.ssu.ac.ir/browse.php?a_code=A-10-722-1&slc_lang=en&sid=1 Karim ebrahimpour K.ebrahiim@gmail.com 0000-0002-6230-0119 No Department of Environmental Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran. Afshin Ebrahimi a_ebrahimi@hlth.mui.ac.ir 0000-0002-3640-087X No Department of Environmental Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran. Morad Mahmoudi Baram m_mahmoodi95@yahoo.com 0000-0003-2349-5387 Yes Department of Environmental Health Engineering, School of Health, Isfahan University of Medical Sciences, Isfahan, Iran.