Revolatilisation of soil-accumulated pollutants triggered by the summer monsoon in India

Gerhard Lammel,Sachin S Gunthe,Petra Příbylová,Marie D Mulder,Ondřej Audy,Céline Degrendele,Irene Stemmler,Qing Mu,Petr Kukučka,Pourya Shahpoury,Akila Muthalagu,Mega Octaviani,Aswathy E Valsan,Chelackal V Biju

doi:10.5194/acp-18-11031-2018

Abstract

Abstract. Persistent organic pollutants that have accumulated in soils can be remobilised by volatilisation in response to chemical equilibrium with the atmosphere. Clean air masses from the Indian Ocean, advected with the onset of the summer monsoon, are found to reduce concentrations of hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT) and its derivatives, endosulfan and polychlorinated biphenyls (PCBs) in air at a mountain site (all in the range 5–20 pg m−3) by 77 %, 70 %, 82 % and 45 %, respectively. The analysis of fugacities in soil and air suggest that the arrival of summer monsoon triggers net volatilisation or enhances ongoing revolatilisation of the now-banned chemicals HCH and PCBs from background soils in southern India. The response of the air–soil exchange was modelled using a regional air pollution model, WRF-Chem PAH/POP. The results suggest that the air is increasingly polluted during transport by the south-westerly monsoon winds across the subcontinent. Using a multidecadal multimedia mass balance model, it is found that air–surface exchange of HCH and DDT have declined since the ban of these substances from agriculture, but remobilisation of higher chlorinated PCBs may have reached a historical high, 40 years after peak emission.

Highlights

Persistent organic pollutants that have accumulated in soils can be remobilised by volatilisation in response to chemical equilibrium with the atmosphere
The analysis of fugacities in soil and air suggest that the arrival of summer monsoon triggers net volatilisation or enhances ongoing revolatilisation of the now-banned chemicals HCH and polychlorinated biphenyls (PCBs) from background soils in southern India
Using a multidecadal multimedia mass balance model, it is found that air–surface exchange of HCH and DDT have declined since the ban of these substances from agriculture, but remobilisation of higher chlorinated PCBs may have reached a historical high, 40 years after peak emission

Summary

Introduction

Persistent organic pollutants pose a hazard to humans and wildlife as they may reach harmful concentrations in biota upon accumulation along food chains. Semi-volatile substances (i.e. vapour pressure at 293 K in the range 10−6– 10−2 Pa) diffuse across air–sea and air–land interfaces in both directions. They tend to net volatilise from land and sea surfaces on which they had previously been deposited once a level of contamination in chemical equilibrium with air pollution was reached (Bidleman, 1999; Cousins et al, 1999; Meijer et al, 2003; Kurt-Karakus et al, 2006; Wong et al, 2007; Ruzicková et al, 2008; Degrendele et al, 2016). Understanding the dynamics of soil contamination and exchange with the overlying air is important for assessing spatio-temporal scales of the distribution and impact of local

Methods

Results

Conclusion