Assessment of the porong river health based on the reactivity of aquatic sediment to the bioavailable zinc

Abstract

The Porong River in Sidoarjo Regency, East Java, Indonesia has received the natural mud, called Lapindo mud, resulting from anthropogenic waste containing zinc that can settle in the aquatic sediment. Assessment of bioavailability of zinc distribution in the aquatic sediment is important in determining the role of sediment for zinc in long term that imposes ecotoxicological problems. The aim of this research was to determine the distribution of bioavailable zinc in Porong River sediment and to assess the sediment reactivity in providing bioavailable zinc based on the Risk Assessment Code (RAC) value. Sampling was conducted at two sites along the Porong River, Sidoarjo, East Java, Indonesia. These sites were in the Brantas downstream, which had received municipal and industrial waste containing zinc. Sediment samples were collected using an Eickman Grab sampler and stored in the dark in a sealed plastic bag at 4°C. Geochemical fractions of zinc in the sediment were extracted using the European Community Bureau of Reference (BCR) method for four stages. Zinc concentration was analyzed using atomic absorption spectrophotometry (AAS). Results showed that the total concentration of zinc in the sediment of the first site was lower than the concentration in the second site. The non-resistant fraction of zinc in the first site was lower than the concentration in the second site. Conversely, the resistant fraction in the first site was higher than the concentration in the second site. As a non-resistant fraction, zinc was predominantly found as an acid reduction fraction with a concentration of 24.7 mg/kg (site 1) and 30.9 mg/kg (site 2). The concentration of the organic oxidation fraction of zinc was lower than the concentration of the acid reduction fraction. Meanwhile, the bioavailable fraction of zinc was the lowest at 9.6 mg/kg for the first site and 15.1 mg/kg for the second site. Based on these results, it was determined that the sediment of the Porong River had medium reactivity for the bioavailability of zinc with RAC values of 13.3% and 15.4% for the first and second sites, respectively.