Modeled direct photolytic decomposition of polybrominated diphenyl ethers in the Baltic Sea and the Atlantic Ocean

In this study, tetra- (#47), penta- (#99), and decabrominated (#209) diphenyl ethers were exposed (in isooctane) to summer sunlight at 60 degrees N, where their photochemical half-lives ranged from 0.6 to 203 h. Apparent quantum yields, ranging from 0.16 to 0.28, were applied to optical models to calculate the rates of direct photochemical decomposition at the surface (depth of 0 m) and in the mixing layer of the ocean. The calculated photolytic half-lives were 4-100 times as long in the mixing layer of the Baltic Sea and the North Atlantic Ocean as atthe surface of 0 m. Calculation of seasonal photochemical half-lives for the mixing layer of the North Atlantic Ocean from 0 degrees N to 60 degrees N showed that the solar photolysis effectively decomposes the congeners in the tropics. At mid- and high latitudes, where solar irradiances are lower outside summer, the photolysis rates for congeners #47 and #99 were often too low for their effective decomposition in the mixing layer. Although solar radiation can potentially decompose the congeners in the mixing layer of the ocean effectively, seasonal and latitudal variation in solar irradiance as well as optical and mixing properties of the ocean can make the direct photolytic decomposition ineffective at high latitude and the coastal ocean.