Effect of HNO and HSO on the Paddy Ecosystem: A Mesocosm Study with Exposure at PNEC and HC Levels.

Paddy mesocosms comprising of rice (), snail (), and worm () were used to assess the damage caused by two acids (HNO and HSO) at predicted no-effect concentration (PNEC) and hazardous concentration for 50% of species (HC) levels. In the fourth week, the fresh weight and shoot height of at HSO-HC were reduced by 83.2% and 30.3%, respectively. Wilted leaves (%) at HC were approximately twice that at PNEC. No and were recovered at HC. At HSO-PNEC, the length and weight of were reduced by 7.4% and 25.9%, respectively, whereas fewer adult (46.5%) and juvenile (84%) were recovered. In the 20th week, rice growth and productivity were correlated with initial pH (pH) and nitrogen levels. Poor correlation with chlorophyll at the active tillering stage suggests the disturbance of nutrient uptake by roots. Partial least squares path modeling (PLS-PM) results further supported that the pH directly affects grain yield and quality, as well as plant growth. The indirect effect via intervening fourth-week-variables was also substantial. Therefore, it is important to measure initial pH upon acid spill to estimate the risk to the paddy ecosystem. Information on the change in soil properties associated with acidity will also aid in predicting the yield and quality of grain to be harvested.