Heavy metals accumulation in selected weed species under oil palm plantation in Carey Island, Selangor / Linda Jiren

Application of agrochemicals such as pesticides and fertilizers in oil palm plantation is a common practice. Heavy metals are known to be part of the residue component of most pesticides and naturally occurring inorganic as well as organic fertilizers. Some weed species are able to absorb heavy metals from soil in large amount and can be used for phytoremediation. This study determined the demography of weed species under oil palm plantation in West Estate, Carey Island. This study also to evaluate the content of Arsenic (As), Cadmium (Cd), Mercury (Hg), Lead (Pb) and Nickel (Ni) in soil and weed species under oil palm plantation in West Estate, Carey Island. Then, this study assessed the pattern of arsenic uptake and accumulation by Axonopus compressus, Ageratum conyzoides and Borreria latifolia. The sampling site was conducted in oil palm plantation located in Carey Island, Selangor aged 3, 10 and 17 years old in 2011. A survey census of weed species under the three ages of palm oil was conducted. Weed species were identified, counted and recorded. Random sampling of soil from 0-20 cm depth taken at 12 different points. Soil samples were analyzed for As, Cd, Hg, Pb and Ni, pH, EC, C and soil texture. Identified weed species with soil were collected to analyze for the content of As, Cd, Hg, Pb and Ni. Heavy metal concentrations in plant and soil were measured by Inductively Coupled plasma Optical Emission Spectrometry (ICP-OES). The results showed that under 3 years old oil palm stand, 6 different species belonging to 4 families were recorded while for 10 years old oil palm stand there were 11 different species belonging to 7 families and for 17 years old oil palm stand 9 different species belonging to 5 families were recorded. Ischaemum muticum Linn was the dominant species in the 3 years old plot (83.24%) while Axonopus compressus was the dominant species under 10 and 17 years old plot (50.14% and 80.27%). As concentration in soil showed a steady increase with age of oil palm indicating potential accumulation with range between 17.58 to 31.65 mg/kg. Arsenic and Pb recorded were significantly different concentrations (P>0.001) and so was Hg (P>0.014) respectively, while the concentrations of Ni and Cd in soil were not significantly different across different oil palm ages. Under 3 years old oil palm, Borreria setidens was able to absorb the highest concentration of As, Cd, Ni, Pb and Hg (6.54, 3.87, 25.82, 29.66 and 0.06 mg/kg). Under 10 years old oil palm stand, Borreria setidens absorbed the highest concentration of As (8.52 mg/kg) and Cd (4.59 mg/kg). The highest concentration of Pb was absorbed by Centotheca lappacea (Linn.) Desv (59.638 mg/kg) while Adiantum latifolium Lam absorbed the highest concentration of Ni (100.877 mg/kg) and Hg (0.07 mg/kg). Under 17 years old oil palm stand, Borreria latifolia accumulated the highest concentration of As (26.66 mg/kg) followed by Borreria setidens (7.41 mg/kg), Asystasia gangetica (3.96 mg/kg) and Axonopus compressus (2.84 mg/kg). Asystasia gangetica absorbed the highest concentration of Pb (15.87 mg/kg) and Ni (5.38 mg/kg) while Cleome rutidosperma absorbed the highest concentration of Cd. A hydroponic experiment to determine the pattern of As accumulation in Axonopus compressus, Ageratum conyzoides and Borreria latifolia was carried out. Based on the hydroponic study, Ageratum conyzoides showed the highest potential of absorbing As (6666.33 mg/kg) compared to Axonopus compressus (1914.33 mg/kg) and Borreria latifolia (4654.67 mg/kg) under concentration range 20, 40, 80 and 160 mg/kg.