The impact of expressway snowmelt agent usage on the environment in an extreme freezing snow and sleet condition

During Jan 11-Feb 2, 2008, affected by cold air, a rare cryogenic sleet and snow weather process occurred in the southern China. To cope with this extreme weather condition, and to secure the expressway safety, for the first time some expressways used snowmelt agent in large areas. In order to make quantitative impact assessment for the snowmelt agent usage on roadside ecological environment under these extreme sleet and snow condition, field sampling surveys were conducted on the North Guangdong section and the Hunan Leiyi section of Beijing-Hong Kong-Macao Expressway, where the most snowmelt agent used on, in March 2008. The results showed that the snowmelt agents were dominated by salts, of which the main components are sodium chloride (NaCl) and sodium sulfate (NaSO₄). After deicing, the concentrations of chloride, sulfate and sodium ions in water sampling from drainage edge ditches were (19.89±19.11) mgL⁻¹, (45.73±29.67) mgL⁻¹ and (14.41±16.65) mgL⁻¹, respectively, which is 3.07 times, 2.08 times and 8.58 times that in the water outside the ditches; and these ion concentrations outside the ditches are slightly higher than that in the river nearby. The concentrations of these ions in the soil within 20 meter range of vertical distance from road exhibited a downward trend with the increase of distance from road. In the soil close to expressway (0.5-2.5 m), the main components of snowmelt agents accumulated within the depth of 10-20 cm; and soils a little bit far from expressway are not affected. In some road section, snow residue containing snowmelt agents were concentrated on roadside plant growth area, where the vegetation were killed by salt damage.