Determination Of Hydrogen Peroxide In Natural Waters And The Biogeochemical Behavior Of Hydrogen Peroxide

H₂O₂ plays an important role in photochemical and redox reactions in natural water systems and it can affect the fate of organic compounds, and is one of the major reasons to the acidification of rainwater. As a result, it's significant developing methods for H₂O₂ measurement and study on the biogeochemical behavior of H₂O₂ in various waters.The measurement method of H₂O₂ in natural waters has been improved in our lab based on the references. This method can be used to analyse H₂O₂ in seawater, rainwater, groundwater and reservoir water simultaneously. The optimum conditions are as followed: p-hydroxylphenylacetic acid: 5×10-4mol/L; peroxidase: 250units/L; catalase: 850 units/L and decompose 4-5 minutes; the buffer is made up of Tris(0.25 mol/L) and HCL(0.5mol/L), pH=8.8. Under these conditions the fluorescence signal is stable within four hours. The detection line (LOD) of H₂O₂ is 5nmol/L and relative standard deviation (RSD) is less than 5%. The method can be used to determine the concentration from 0 to 10-4mol/L. The results obtained by this method and references'have no obvious difference.The concentrations of H₂O₂ in rainwater of the Changjiang Estuary and Qingdao were determined in the summer, 2006. The average concentrations of H₂O₂ in rainwater are respectively with 7.308μmol/L in Qingdao and 39.029μmol/L in Changjiang Estuary respectively. The H₂O₂ concentration in rainwater has no obvious correlation with the time of rain lasting, pH and ambient temperature. The H₂O₂ concentration in rainwater is affected by rainfall lightning and the weather conditions before raining.In May 2006, seawater samples were collected in Jiaozhou Bay. H₂O₂ in surface waters shows obvious diurnal variations. Photochemical reactions maybe the predominant source of H₂O₂. Affected by vertical mixing and water exchange between the bay and Yellow Sea, H₂O₂ in the middle and bottom layers is not obvious. The concentrations of H₂O₂ decrease with increase in depth.H₂O₂ concentrations were measured for samples collected in August and October 2006 in the Changjiang Estuary. Compared with other areas, in August, concentrations of H₂O₂ in surface waters are higher and varied with broad range; In October, H₂O₂ concentrations are lower and varied with narrow range. This is affected by phytoplankton, freshwater discharge, solar radiation, wet deposition and so on. In August, H₂O₂ in surface water shows diurnal variations with maximum concentrations at 3 pm. Photochemical reactions are the major source of H₂O₂ in August affected by wet deposition. In October, H₂O₂ in surface water shows diurnal variations too, but photochemical reactions are not the mainly source of H₂O₂. The vertical profile of H₂O₂ showed three types: 1.surface maximum, the H₂O₂ concentration decreased gradually with depth; 2. Surface mixed and H₂O₂ concentrations were stable in the mixed layer and the H₂O₂ concentrations decreases gradually below the mixed layer; 3.Subsurface or thermocline maximum. The wet deposition of H₂O₂ is estimated to be 1.32¹.65×10^-2mol/m² in the Changjiang Estuary.