Removal of MCPA and 2,4D from water and mitigation of phytotoxicity using Vacuum UV treatment

Master Thesis - MSc in Environmental Science, Candidate in Technology - Aalborg University

Romanelli - MSc thesis.pdf

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Freshwater is crucial for food production and human health, but it is unevenly distributed globally and not fully available for use. Freshwater for food production and drinking water is available as groundwater and as surface as water in rivers and lakes. However, the water quality is decreasing due to pollution from human activities. The chemical compounds emitted to the environment due to runoff and leaching threaten the use of water, for human consumption and for irrigation in agriculture, potentially affecting health and crop yield respectively. MCPA and 2,4D are the most common selective herbicides used worldwide, and have been detected in ground and surface waters around the world.

These chemicals can have adverse effects on non target aquatic organisms such as algae, and terrestrial organisms such as soil bacteria and commercial crops but the concentration effect-range is still being investigated. Thus, there is increasing focus on removing these chemicals from the water cycle to reduce risks associated with use of water for irrigation and human consumption.

This project aims to determine the degradation of MCPA and 2,4D during an Advanced

Oxidation Processes (AOP) with Vacuum UV (VUV) irradiation, and to determine

the acute ecotoxicity before and after treatment to Lactuca sativa (Lettuce), Lepidium

sativum (Cress), Raphidocelis subcapitata (a green microalgae) and Bacillus subtilis (a soil bacterium). Toxicity was determined as the EC50 based on growth, after exposing the test organisms to different concentrations of MCPA or 2,4D for a period of 18 to 120 hours, depending on the species. VUV was run for MCPA and 2,4D at an initial concentration of 10 mg/L dissolevd in 4 L of tap water, and samples were taken at 0, 1, 2, 4, 8, 16 and 32 minutes. Remaining concentrations after VUV at each time point, were measured by HPLC using separation in a C18 column with a mobile phase of acetonitrile and a buffer solution at PH 4. The wavelength for UV detection of MCPA and 2,4D was set 230 nm. The initial EC50 values was 0.029mg/L for MCPA and 0.041mg/L for 2,4D using Lepidium sativum as test organism; 0.017mg/L for MCPA and 0.068 for 2,4D using Lactuca sativa; 50mg/L for MCPA and 100mg/L for 2,4D using Raphidocelis subcapitata, and >100mg/L for MCPA and 2,4 D using Bacillus subtilis.

Vacuum UV treatment completely removed the initial concentration (10 mg/L) of MCPA

and 2,4D after 8 and 32 minutes, respectively. The decay rate coefficient resulted

in 0.87(min-1) for MCPA and 0.16 (min-1) for 2,4D. The VUV degradation of 2,4D

and MCPA was reflected in increasing apparent EC50 values. For Lactuca sativa and

Lepidium sativum, the toxicity decreased 4-1.5 fold and 7-8 fold after VUV treatment of

compound MCPA for 2 and 4 minutes, respectively. After VUV treatment of 2,4D, toxicity

forLactuca sativa and Lepidium sativum decreased 2-0.57 fold and 4-1.16 fold a times 2

and 4, respectively.