Distribution and Speciation of Heavy Metals in Soils Irrigated with Wastewater in Braunschweig, Germany and Konya, Turkey
Nina Hamidah, Dr. rer.nat. Ria Armunanto, M.Sc.
2012 | Tesis | S2 Ilmu Kimia-
A six-step sequential extraction had been done to study the bonding forms of main and trace elements in selected soil samples of two irrigation areas in Braunschweig, Germany, and Konya, Turkey, and compared with non irrigated reference soils with similar properties. In addition, the climates and soils of the two irrigated areas (Braunschweig and Konya) have totally different properties. These two factors offer an interesting case study to compare different practices of long term irrigation using reclaimed wastewater under different conditions. Seven different bonding forms were identified for each fraction: 1) soluble; 2) exchangeable; 3) carbonatic; 4) easily reducible; 5) moderately reducible; 6) oxidizable and 7) residual. Prior to the sequential extraction procedure, soil samples were analyzed for their characteristics such as grain size classification, soil pH, total organic carbon (TOC) and total metal contents. Element analysis for both total and fraction concentrations were done using ICP-OES. The soils from the irrigation fields of Braunschweig were classified as sand or loamy sand, while the soil samples of Konya were classified as silt loam and silty loam clay. The pH values of the soil samples from Braunschweig were generally lower than 7, indicating the absence or a low content of carbonate. On the other hand, Konya soil samples were highly calcareous with an average calcium carbonate contents of 55%, with pH of higher than 8 for most samples. The soils of Braunschweig had higher average TOC contents (2.05 %) than the soils of Konya (1.04 %). Chemical sequential extraction of irrigated soil from Braunschweig indicated a relatively low environmental risk of PTEs. For most PTEs, more than 40% occurred in residual fraction, and only Pb and Cu occurred in less than 20% in the residual fraction. Meanwhile, the concentrations of trace elements in the soil irrigated by wastewater in Braunschweig were generally only slightly higher than that in the reference soil samples which were not irrigated using wastewater. For example, Zn was present between 118 – 131 mg/kg in the irrigated soils, and between 56.8 – 98.4 mg/kg in the reference soils of Braunschweig. With about 66% occurring in the non-residual fractions, Zn is the trace element with highest environmental relevance in the soil of Braunschweig. Results of sequential extraction of Konya soil showed considerably different results, most likely due to highly calcareous structure of the soil. Soils from irrigated fields generally have lower PTEs concentration compared to that of Brausnchweig, which made it difficult for instrumental detection after speciation. The sediment excavated directly from the bank of the main drain channel, which transports the wastewater from the City Konya to the Salt Lake (Tuz Gölü), shows a noticeably different element composition in comparison to the samples of the irrigated fields as well as reference soils, with a slightly lower Ca concentration. However, the concentration of Cr and Cu is almost three times higher than in the irrigated soils, while Zn is almost six times higher. Contamination of PTEs in the irrigated soils is only apparent for Ni and Zn, with concentrations of about three times higher than the concentrations in the reference soils. The concentration of Ni in the irrigated soils (124 mg/kg) is higher than the limit value suggested by the Germany Sewage Sludge Ordinance (1992) for agriculture soils (50 mg/kg). Meanwhile, although the concentration of Zn in the irrigated soils is lower than the limit value suggested by the same regulation, more than 80% occurred in the more mobile non-residual fractions (Fractions 1-6), in contrast to about 80% of residual fraction (Fraction 7) in the reference soils. The irrigated soils also contained Cu and Cr with concentrations of about twice as much as in the reference soils.
Kata Kunci : Braunschweig, heavy metals, irrigation, Konya, PTE, sequential extraction, wastewater
