Abstract
Glyphosate (GLY) is a major herbicide used throughout the world, and its continuous application has become an environmental issue. Adsorption is an important mechanism for removing organic contaminant in water. The present study characterized cow dung (CD) and rice husk ash (RHA), and determined the adsorption-desorption of GLY and its metabolite, aminomethylphoshonic acid (AMPA), on to them. The results revealed that both CD and RHA were alkaline and had no or low content of arsenic, cadmium, chromium and lead. The CD had lower surface area (13.104 mg2g−1) than RHA (21.500 m2g−1). The CD contained amines, phenol, ethers and carboxylic functional groups, while in addition to carboxylic and ether, RHA contains siloxane. Both CD and RHA had high affinities for GLY and AMPA. The Freundlich sorption coefficient (Kf) on AMPA were 2.915 and 2.660 for CD and RHA, respectively, while the values on GLY were 1.168 and 1.166 (mg g−1) for CD and RHA, respectively. Desorption of GLY only occurred at lower concentrations, while no desorption of AMPA was recorded, indicating their strong adsorption on CD and RHA. Considering their availabilities and affordable prices, both CD and RHA can be recommended as economical adsorbent for the removal of GLY and AMPA.
Highlights
Glyphosate {N-(phosphonomethlyl) glycine} (GLY) is a broad spectrum herbicide commonly used in Malaysia and it acts by disrupting the shikimic pathway in plants necessary for the synthesis of essential amino acids-phenylalanine, tyrosine and tryptophan1- resulting to the death of plant
The results show that the Cow dung (CD) contained 30.78% C, 4.79% H, 40.26% O, 2.53% N and 0.23% S, while Rice husk ash (RHA) contained 1.83% C, 1.93% O and 0.19% S, and H and N were below detection levels, which can be attributed to their oxidization during combustion
The porous nature of CD and RHA is an indication of their high surface area owing to the large micro and macro pores, which drive their adsorptive capacity[28]
Summary
Glyphosate {N-(phosphonomethlyl) glycine} (GLY) is a broad spectrum herbicide commonly used in Malaysia and it acts by disrupting the shikimic pathway in plants necessary for the synthesis of essential amino acids-phenylalanine, tyrosine and tryptophan1- resulting to the death of plant. On one hand Piel et al.[10] reported that, AMPA occurs widely in surface water of France, with higher concentration in urban water (5 μg L−1) than in rural water (2 μg L−1) Given these instances, removing GLY and AMPA from the water body is of great environmental significance. Other constraints associated with these methods are high operational and maintenance cost, complicated procedure in their operation and generation of toxic compounds[12] For these reasons, adsorption serve as an effective method of removing water-soluble pesticide like GLY from water[13]. Their functional groups and cation contents enhance their adsorption capacities in relation to GLY and AMPA These agricultural wastes are abundantly available in Malaysia at a very low cost. The present study aimed to characterize CD and RHA and investigate their adsorption-desorption for GLY and AMPA in a single-solute system
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