Occurrence, enantiomeric signature and ecotoxicological risk assessment of HCH isomers and DDT metabolites in the sediments of Kabul River, Pakistan

Abstract

Hexachlorocyclohexane (HCH) isomers and dichlorodiphenyltrichloroethane (DDT) metabolites were analyzed in sediments of three different depths (0-10, 10-20 and 20-30 cm) collected from Kabul River, Pakistan, in February 2014. The occurrence levels, enantiomer fractions and potential ecological risk of these organochlorine pesticides (OCPs) were evaluated. The total concentrations of ∑HCHs and ∑DDTs in surface sediments ranged from 4.9-23.9 ng g and from 6.4-18.8 ng g (dry weight basis), respectively. The vertical contamination profile of DDTs was found in order of 20-30 cm >10-20 cm >0-10 cm, indicated that the residue levels of DDTs gradually decreased after it was banned. The ratios of β-HCH/HCHs ranged from 0.04 to 0.73 (69 % of samples below 0.5) suggesting the fresh input of HCHs, while isomeric ratios of α-HCH/γ-HCH (ranged from 0.02 to 7.94), with 76 % of samples less than 3, indicating the cocktail use of technical grade HCH and lindane in the study area. The ratio of (DDE + DDD)/DDTs (ranged from 0.42 to 0.90) indicated long-term biodegradation of parent DDT. The enantiomer of α-HCH was generally racemic or close to racemic for most of the samples, with enantiomeric fraction (EF) value <0.5 for some of the samples indicated the preferential biodegradation of (+)-α-HCH enantiomer, while for o,p'-DDT the EF values >0.5 indicated the depletion of (-)-o,p'-DDT enantiomer in most of the samples. According to sediment quality guidelines (SQGs), HCH contamination is the main concern for ecotoxicological risk in Kabul River.

Reconnaissance Survey of Organic Contaminants of Emerging Concern in the Kabul and Swat Rivers of Pakistan

“…Upstream sites on the Swat River were <LOD. In addition, many legacy pesticides used in the region were not included in the present study because they have been previously reported (Aamir et al, 2017; Saad et al, 2017). For example, endosulfan is a commonly used pesticide reported at concentrations up to 166 ng/L in the Indus River (Shaikh et al, 2014).…”

“…The majority of contaminant studies in Pakistan have focused on metals and pesticides in portions of the Indus River basin downstream of Khyber Pakhtunkhwa in Sindh Province (Mirbahar et al, 2020;Scheurell et al, 2009) or Punjab Province (Ashfaq et al, 2016(Ashfaq et al, , 2019Ashfaq, Khan, et al, 2017;Ashfaq, Noor, et al, 2017;Riaz et al, 2023). In the Khyber Pakhtunkhwa, prior contaminant studies focused primarily on metals in the Kabul (Ali & Khan, 2018;Aamir et al, 2017;; M. I. T.…”

“…The majority of contaminant studies in Pakistan have focused on metals and pesticides in portions of the Indus River basin downstream of Khyber Pakhtunkhwa in Sindh Province (Mirbahar et al, 2020; Scheurell et al, 2009) or Punjab Province (Ashfaq et al, 2016, 2019; Ashfaq, Khan, et al, 2017; Ashfaq, Noor, et al, 2017; Riaz et al, 2023). In the Khyber Pakhtunkhwa, prior contaminant studies focused primarily on metals in the Kabul (Ali & Khan, 2018; Aamir et al, 2017; K. Khan et al, 2022; M. I. Khan et al, 2018; T. Khan et al, 2011; Muhammad & Usman, 2022; Saad et al, 2017; Usman et al, 2017) and Swat rivers (Alam et al, 2020; Jehan et al, 2020; K. Khan et al, 2022; L. Khan et al, 2022; M. Khan et al, 2022; M. Liu et al, 2020; Muhammad & Usman, 2022; Sohail et al, 2022). Only a few studies in Pakistan have reported the occurrence of CECs in freshwater reservoirs, river water, and wastewater discharges in portions of the Indus River basin downstream of Khyber Pakhtunkhwa in Sindh Province (Mirbahar et al, 2020; Scheurell et al, 2009) or Punjab Province (Ashfaq et al, 2016, 2019; Ashfaq, Khan, et al, 2017; Ashfaq, Noor, et al, 2017; Riaz et al, 2023).…”

Historical Records and Source Apportionment of Organochlorine Pesticides (OCPs) in a Sediment Core from Songhua Lake, Northeast China

“…Ecotoxicological risk assessment refers to the effective prediction of the possible ecological effects caused by toxic pollutants in the environmental media and the method of assessing the probability of risk occurrence. Contaminated sediments can pose potential ecological risks to the aquatic ecosystem [32]. In this study, a level-screening ecotoxicological risk assessment was conducted using two international sediments quality guidelines (SQGs), the threshold effects level (TEL), probable effects level (PEL) guidelines proposed by Macdonald et al (1996) [33], and the effects rangelow value (ERL), effects range-median value (ERM) guidelines proposed by Long et al (1995) [34].…”