| Resumo: |
The objective of our studies is to analyze environmental impacts of Monosodium Methane Arsenate, MSMA, on aquatic habitats using the Aqua-Terra microcosm system. MSMA was applied at environmentally relevant(recommended) doses to microcosms to determine the change in biodiversity and the bio-concentration of arsenic in the aquatic plants (_Elodea Sp._) used in the microcosms as an oxygen source. The microcosms are filled with unfiltered pond water and the diversity of each microcosm was determined before application of the herbicide. After population stabilization, the herbicide is applied to the terrestrial portion of the microcosm. The herbicide is watered into the microcosm by allowing the herbicide to be filtered by soil into the aquatic portion of the microcosm. Diversity of the microcosm was determined by physical counts of invertebrate organisms and quantified using Simpson’s Index of Diversity. Calculating Simpson’s Index of Diversity indicate there is an overall decline in the diversity of the microcosms from 0.327 to 0.763 for recommended manufacturer’s formulation and 0.512 to 0.546 for twice the recommended manufacturer’s formulation. 

Plants take up arsenic using the same metabolic pathways that they use to take up phosphorus. This makes arsenic available for trophic transfer to the primary consumers as any primary producer is consumed. In _Elodea sp._, total arsenic concentrations (ashed from fresh samples) range from 15 ppb to 214 ppb before and after application of the herbicide. Water samples show the same increase, from 5 ppb to 70 ppb before and after application. These data indicate that the arsenic in the MSMA compound is either being liberated by bacterial decomposing or it is passing through the soil unmodified.

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