## 4 Conclusions  
In this study, SPME coupled to the GC-ECD method was successfully developed for the extraction and determination of 20 chlorinated pesticides in surface water samples. The SPME method is fast, effective, simple, more environment friendly and decreases expenditures and time required for sample preparation and analysis. It is a good alternative to conventional sample extraction techniques such as liquid-liquid extraction (LLE) and solid phase extraction (SPE) without using expensive and toxic solvents or expensive extraction equipment. The SPME-GC-ECD method showed high extraction efficiency, good percent recoveries (87.5% to 106.0%) and acceptable LODs (0.002 to 0.03 \(\upmu\)g L\({}^{-1}\)) for all 20 chlorinated pesticides, which were much lower than their maximum permissible contamination levels. These results indicated that this system is a sensitive, cheaper and simpler alternative to mass spectrometry for assessment the presence of organochlorine pesticides residues in water samples. About 50% of the surface water samples collected from Charsadda district were found to be contaminated with pesticides such as \(\gamma\)-BHC, heptachlor, aldrin and dieldrin. Contamination from the major pesticides was found at maximum values of 0.023 \(\upmu\)g L\({}^{-1}\) (\(\gamma\)-BHC), 0.108 \(\upmu\)g L\({}^{-1}\) (heptachlor), 0.014 \(\upmu\)g L\({}^{-1}\)(aldrin) and 0.013 \(\upmu\)g L\({}^{-1}\) (dieldrin) in the surface water samples of the Charsadda area. For adults, the cancer risk from water due to contamination of various pesticides ranged from 0 to 15.53 \(\times\) 10\({}^{-6}\)\(\upmu\)g L\({}^{-1}\). The non-carcinogenic risk found from each pollutant in the water samples was in the order of aldrin > dieldrin > heptachlor > \(\gamma\)-BHC. Similarly, for children, the cancer risk ranged from 0 to 33.29 \(\times\) 10\({}^{-6}\)\(\upmu\)g L\({}^{-1}\) and non-carcinogenic risk was found in the order of heptachlor > aldrin > dieldrin > \(\gamma\)-BHC. The SPME coupled to GC-ECD has been found to be an excellent approach for the analysis of chlorinated pesticides in water samples. **Author Contributions:** Conceptualization, M.L; methodology, N.u.R., Z.V.-G., G.R.; software, S.A.; validation, I.Z., M.S.K. and M.Z.; formal analysis, A.K., J.B.; investigation, I.Z., A.K., N.P.; resources, M.Z.; data curation, N.R.; writing--original draft preparation, N.u.A., I.Z., S.M.M.S., M.W. and Y.J.; writing--review and editing, I.Z.; visualization, L.A.S.; supervision, M.Z.; project administration, M.Z.; funding acquisition, M.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by project nr T190087 MIMV and European Commission, MLTKT19481R \"Identifying best available technologies for decentralized wastewater treatment and resource recovery for India, SLTKT20427 \"Sewage sludge treatment from heavy metals, emerging pollutants and recovery of metals by fungi and by project KIK 15392 and 15401 by European Commission.  
Not applicable.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.