Assessment of the impact of reforestation on soil, riparian sediment and river water quality based on polyaromatic hydrocarbon pollutants

Abstract

This study aimed to assess the impact of the eThekwini Municipality reforestation project on the quality of the soil within the reforestation sites, and water from the nearby rivers (White and Black Mhlasini Rivers) situated at the reforested Buffelsdraai area in KwaZulu-Natal, South Africa. This was the first evaluation of the effect of reforestation on the reduction of selected organic pollutants to be conducted in this area. The sixteen polyaromatic hydrocarbons analysed are on the Environmental Protection Agency (EPA) list of priority pollutants. The soil and sediment samples were extracted using ultrasonication, and liquid-liquid extraction was utilised for the water samples. Gas chromatography mass spectrometry (GCMS) was used to analyze the PAHs. PAH recoveries ranged between 60 and 110%. The PAH LOD values were between 0.30 and 0.69 μg g−1 and LOQ values ranged between 0.99 and 1.9 μg g−1. The total PAH concentrations determined were between 4.258 and 6.426 μg g−1 in the soil samples, 2.210–13.900 μg g−1 in sediment, and 6.360–85.468 ng L−1 in river water. A comparison between all samples and their respective control, showed that reforestation is potentially reducing the concentration of PAH pollutants. The concentration of pollutants was determined to be lower within the reforestation boundaries and higher outside the reforestation boundary. The total concentration for specific PAHs was above the threshold value for most sampling sites according to Canadian environmental guidelines.