Degradation of sulphur containing s-triazines during water chlorination

The reactions of four sulphur containing s-triazines (prometryne, terbutryne, ametryne and desmetryne) with hypochlorous acid (HClO) and chlorine dioxide (ClO₂) have been investigated using an 11 ppm/3 ppm oxidant/herbicide ratio. The main objective of the study was the identification of by-products. Additionally, to study the effect of oxidant concentration on the reaction rate, two more oxidant/herbicide ratios (3 ppm/3 ppb and 11 ppb/3 ppb) have been investigated only for prometryne. Oxidation reactions were monitored by high performance liquid chromatography (HPLC), while, the identification of by-products was initially carried out by low resolution HPLC-mass spectrometry (HPLC-MS) and confirmed by accurate mass measurement. Under the experimental conditions (T = 20°C, pH = 8, reaction TIME = 48 h), the results indicate that all the investigated triazines react in the same way with each oxidant. The reactions with HClO occur much faster than those with ClO₂ and give rise to three identified oxidation by-products: the sulfoxide, the sulfone and the sulfone's hydrolysis product. The reactions with ClO₂, instead, give rise to a sole oxidation by-product: the sulfoxide. With both oxidants, as expected, the lower the oxidant concentration the slower the oxidation rate.

Based on the obtained results, a general pathway for the oxidation of sulphur containing s-triazines is proposed.     

Inhibition of algal photosynthesis to control pH and reduce ammonia volatilization from rice floodwater

When urea or ammoniacal-N fertilizers are applied to the floodwater of a rice crop, fertilizer use efficiency is often reduced because there are substantial losses of NH₃ by volatilization. As pH rises the potential loss increases exponentially due to the increasing dominance of volatile NH₃ gas in equilibrium with NH ₄ ⁺ . We postulate that the daytime pH rise is caused mainly by photosynthesis of algae and Cyanobacteria, and that addition of a suitable photosynthetic inhibitor, concurrently with fertilizer, should suppress the pH rise, thus conserving N in the form of the non-volatile NH ₄ ⁺ . We selected terbutryne (2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-s-triazine) as the most promising inhibitor. In rice floodwater fertilized with urea the addition of terbutryne dampened the diurnal fluctuation in pH for 6 days and significantly increased the ammoniacal-N (AN) concentration measured in the floodwater. The concentration of ammonia gas in the air in equilibrium with the water, ₀, which is proportional to the gaseous flux of NH₃ at a given wind speed, was substantially reduced by terbutryne addition. Maximum values were reduced by over 50%. Terbutryne reduced the calculated cumulative NH₃ emission by 43%, relative to the fertilizer (N + P) control. Terbutryne also suppressed photosynthetic oxygen production. Therefore, it may reduce N fertilizer losses by inhibiting nitrification, an aerobic process, so retarding subsequent denitrification losses of gaseous nitrogen and nitrogen oxides.Part of the supporting documentation for Fertilization of Crops. International Patent Application PCT/AU86/00093 filed 11 April 1986.