对二甲苯降解产物对海洋双壳类的急性毒性

为评价微藻降解海水中对二甲苯（PX）的生物安全性，测定了PX降解生成的3种中间产物（对甲基苯甲酸、对甲基苯甲醇和对甲酚）对2种海洋双壳类（菲律宾蛤仔、文蛤）的半致死浓度（LC₅₀），并计算相应的安全浓度.根据国际海事组织（IMO）“海洋环境保护专家组（GESAMP）提出的化学品危害评估程序判断，对甲基苯甲醇（96h LC₅₀=305.67和560.34mg/L）和对甲基苯甲酸（96h LC₅₀>340mg/L）对2种双壳类的急性毒性等级均为“实际无毒”；对甲酚对菲律宾蛤仔、文蛤分别具有“低毒”和“无毒”（96h LC₅₀=77.95和1271.74mg/L）.对甲酚对菲律宾蛤仔的毒性高于文蛤，可能与其在蛤仔体内易于蓄积有关.总体上看，与母体化合物PX（96h LC₅₀>162mg/L）相比，这些中间产物对双壳类的毒性较低，而毒性稍高的对甲酚仅在PX生物降解开始后的短时间内（2~4d）存在，因此，利用微藻降解PX对海洋双壳类具有较好的安全性.对甲基苯甲醇、对甲酚对双壳类的安全浓度分别为70.42和12.10mg/L；但是，对甲基苯甲酸的安全浓度无需给出，因为海水中该化学品的浓度等于其溶解度时，96h内未见双壳类死亡.为全面评价基于微藻的PX污染海域修复技术的生物安全性，今后应加强中间产物对海洋鱼类、甲壳类的毒性研究.

Study on the acute toxicity of degradation products by p-xylene to marine bivalves

To evaluate the application safety of microalgae for p-xylene (PX) biodegradation in seawater, the acute toxicity of three degradative intermediates of PX (p-toluic acid, p-tolyl alcohol and p-cresol) was testified to two species of marine bivalves (Ruditapes philippinarum and Meretrix meretrix), based on which the corresponding safety concentrations (SCs) were calculated. Referring to the revised Hazard Evaluation Procedure for Chemical Substances established by the Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) in International Maritime Organization (IMO), p-toluic acid was "practically non-toxic" on both species with the 96h LC₅₀ values above 340mg/L, as well as p-tolyl alcohol with the 96h LC₅₀ values of 305.67, 560.34mg/L for both species, respectively. While p-cresol was slightly toxic and non-toxic to R. philippinarum (96h LC₅₀=77.95mg/L) and M. meretrix (96h LC₅₀=1271.74mg/L), respectively. It is supposed that a stronger accumulation of p-cresol in R. philippinarum would be related to the higher toxicity compared to M. meretrix. In general, these degradation products showed lower toxicities to bivalves compared with the parent compound, except for p-cresol with a slightly higher toxicity than PX. The application of microalgae for PX degradation is still safe for bivalves because the p-cresol only existed in a short period after PX biodegradation for 2~4 days. The SCs of p-tolyl alcohol and p-cresol to marine bivalves were 70.42, 12.10mg/L, respectively. However, it is not need to propose a limit value of SC for p-toluic acid because the zero mortality of two species occurred when exposed to this compound for 96h at a concentration equal to its solubility in seawater. Further study on the toxicity of these degradative intermediates to marine fishes and crustaceans is needed to obtain a comprehensive understanding of the marine biosafety of PX degradation by microalgae.