Residual Status and Air-Soil Exchange Fluxes of Persistent Organic Pollutants in the Environment of Punjab Province, Pakistan

Abstract

Contamination of different environmental compartments through persistent organic pollutants (POPs) is one of the most impending threats globally. The present study aims to investigate the first systematic data on the levels, distribution, possible sources and air-soil exchange fluxes of persistent organic pollutants (POPs) including organochlorine pesticide (OCPs), polychlorinated biphenyl (PCBs), polybrominated diphenyl ether (PBDEs) and dechloran plus (DP) in the air, surface soil and sediment samples from agricultural and industrial areas of Punjab Province, Pakistan. The present study was conducted in the catchment area of River Ravi from Punjab Province which is the most populated province of Pakistan with a population >90 millions; approximately 56 % of the total population of the country. Surface soils and air samples were taken from ten (10) sampling stations in Punjab Province, while seven (7) sampling stations were selected on the River Ravi to collect surface sediments. Air concentrations of POPs were estimated by using the polyurethane foam passive air sampling (PUF-PAS) technique. Air–soil exchange of POPs was estimated by calculating the fugacities in soil and air samples. Concentrations of ΣOCPs and ΣPCBs were ranged from 121-705 pg m-3 and 35-389 pg m-3 for air samples, 24.6-248 ng g-1 and 6.7-45 ng g-1 for soils and 2.7 to 99 ng g-1 and 4.6 to 424 ng g-1 for sediments, respectively. DDTs and HCHs were dominant OCPs in all air, soils and sediments while among PCBs, tri-, tetra- and penta-CBs was frequently detected homologues. Comparison of OCPs and PCBs concentrations with available sediment guidelines indicated severe contamination of DDTs and PCBs in the study area. Different indicative ratios for organochlorine residues in both soils and sediments suggested current use, long range transport along with past application of these chemicals to the total burden. WHO-TEQ values of dioxin like Σ10PCBs for soil samples obtained were very high and met the limitations, recommended by the Canadian Council of Ministers of the Environment (CCME). Levels of ΣPBDEs and DPs ranged from 8.2-124.7 and 1.5-529 pg m-3 for air, 0.6-501 and 0.1-15 ng g-1 for soil and 1.0-2599 and 0.3-4.7 ng g-1 for sediment samples, respectively. BDE-209 was the most abundant PBDE congener, indicating that deca-BDE accounts for most of the total PBDE emitted in the environment of the Punjab Province. The lower average fractions of anti-DP showed significant differences to those of the technical mixtures, indicating lack of DP production source in Pakistan. In general, POPs level in the current study were found lower and/or within the range of other studies reported throughout the world. Conversely, OCPs and PCBs concentrations in riverine sediments were found much higher than previously reported in Pakistan. Air–soil exchange of POPs was estimated by calculating the fugacities in soil and air samples. In the present study, fugacity fractions (ff) values suggested that soils are acting as a secondary source of DDTs to contaminate the atmosphere at certain sampling stations while other areas showed equilibrium and/or atmospheric deposition status. By our results, it is concluded that globally banned organic pollutants are still used/emitted in the catchment area of River Ravi. Our findings also drew attention that elevated levels of DDTs, HCHs, PCBs (tri- and tetra-), and BDE-209 in the study area must be considered as an important environmental issue and steps should be taken to control excessive discharge of organic pollutants in the local environment. The current study also encouraged to conduct more detailed studies to evaluate the ecotoxicological effects of these contaminants in the environment of Pakistan.