Phytoremediation of Hexavalent Chromium in Effluent Tannery Sludge and Chromium Contaminated Soils by Using Ricinus Communis Plant

Abstract

Heavy metal pollution is a global problem of expanding apprehension due to its toxic effects on the environment which in turn adversely affects Flora and Fauna. Tanning industries have a sludge effluent that is highly contaminated with chromium which is mostly disposed in sludge pits hence polluting the environment. Given the use of chromium in the tanning process and handling of solid wastes in tanning industries, there is high chromium contamination both in the soils surrounding tanning industries and high chromium levels in the tannery effluent sludge after treatment process. The objective of this research is therefore to establish the concentration of chromium VI in tannery effluent sludge; determine the chromium phytoremediation potential of Ricinus Communis (castor oil plant) and Compare efficacy of citric acid as a chelating agent in phytoremediation of chromium VI from chromium contaminated soil and tannery sludge. Samples of tannery sludge were collected from Aziz Tanneries Ltd in Nairobi, and the concentration of Hexavalent Chromium determined using Atomic Absorption Spectrophotometer (AAS). The Ricinus communis seeds were be collected from local castor oil bean plant farmers within Kenya, Germinated, and the Seedlings were transferred to trial pots and watered twice a day and weeded as it deemed necessary. On, thirtieth, forty fifth and sixtieth days the plants were harvested from the pots, cleaned using faucet water and deionized water, and isolated into shoots, stems and roots ready for analysis using the AAS. Bio-Concentration Factor (BCF) and Translocation Factor (TF) were calculated to give the indication of the phytoremediation potential of Ricinus Communis plant. The average concentrations of Hexavalent Chromium (CrVI) Level from the Tannery sludge collected was as 14.936mg/kg this exceeded the United States Environmental Protection Agency (U.S. EPA) regulatory limits for protection of human health and the environment of 0.01mg/kg and the National Environmental Management Authority and WHO limits of 0.05mg/kg. the Hexavalent Chromium concentrations were high at the roots compared to the areal parts in five of the pots at the 30th and 45th day. On the 60th day there was high concentration of hexavalent chromium in leaves, stem and roots of Ricinus communis in tannery sludge media, which infers translocation of the metal. Application of the chelate on the tannery sludge and red soil mixture of ratio 1:1, increased absorption of Hexavalent Chromium. At the 30th day the percentage increase was 39% and more than 100%, from the 45th day. The total accumulation of Hexavalent chromium in R. Communis plant at the end of the exposure period was 11.74 ppm in the pot without chelate and 43.54ppm in the pot with chelate which is approximately 3.7 times more. The bio concentration factor ranged between 0.01 and 2.68. The results in this study showed that Ricinus Communis planted on v Tannery sludge had BCF values > 1 from the 45th day to 75th day. The highest translocation factor (2.524), was noted at 75days exposure time, followed by 1.997 at exposure time of 75days in the chromium polluted soil and soils mixed with tannery sludge (1:1 ratio) respectively. Basically, since the translocation factors were all greater than one at the exposure time of 60 days; this means that Ricinus communis plant has potential for phytoremediation by phytoextraction of chromium with exposure time of between 60 to 75 days. This agrees with Rani, et.al. (2017) on the study on “stabilization of tannery sludge amended soil using Ricinus Communis”, where they concluded that Ricinus Communis plant is suitable for growth in heavy metal rich tannery sludge soil. The Ricinus communis plant, demonstrated potential for phytoremediation of hexavalent chromium by both Phyto stabilization and phytoextraction which may be attributed to its tolerance and considerable biomass production.