Abstract: The fine extinguishing capability of class A foam extinguishing agents are rapidly gaining acceptance. However, with the increasing environmental awareness, recent concern has focused on the potential adverse environmental impact of class A foam discharges. The aim of this study was to evaluate the acute toxicity of class A foam concentrates and solutions used in China. Laboratory studies were conducted to determine the acute toxicity of twelve class A foam extinguishing agents. The organism tested was zebrafish (Brachydanio rerio), and the median lethal concentration (LC50) was calculated and reported. The acute fish toxicity data of Class A foam extinguishing agents both in China and other countries were compared, and the effects of the discharge of class A foam concentrates and solutions on aquatic ecological environment were analyzed. The test results indicate that the 96 h LC50 values of twelve class A foams in China on zebrafish are at the range of 12.85~121.42 mg/L. The acute fish toxicity of Class A foam is significantly higher than that of aqueous film-forming foam (AFFF)(232.57~6 003.25 mg/L). Wetting agents are highly toxic, and they are the most important components affecting the toxicity of Class A foam extinguishing agents, while antifreeze has little influence on the acute toxicity. The acute toxicity values of class A foam both in China and other countries are at the same level, which are mainly within 10~100 mg/L. The 96 h LC50 values of samples meet the acute toxicity limit requirements for class A foam extinguishing agent in NFPA 1150, USDA 5100-307b and other relevant specifications and standards. The concentrate of class A foam extinguishing agent has higher aquatic toxicity than other types of extinguishing agents. According to the guidelines for the hazard evaluation of new chemical substances, it is classified as medium to high toxic substances, and may cause the death of aquatic organisms. So it needs to pay attention to the aquatic toxicity of the concentrate of class A foam. It is advised to operate cautiously in the transportation, storage and transfer of class A foam extinguishing agent concentrates so as to prevent the leakage of concentrates from poisoning natural organisms. The toxicity of class A foam solution is relatively low after being mixed with water at the ratio of 0.1%~1% and then further diluted by natural water body. However, the potential toxic effects of foam solution still exist in the environment. In order to reduce the environmental risk after use of class A foam extinguishing agent, the unnecessary foam disposal should be minimized during fire fighting activities. It is suggested that the foam solution and runoff water should be collected after use and biochemically treated before discharging into the natural environment. In the future research, environment-friendly class A foam extinguishing agent should be developed to reduce the aquatic toxicity and environmental risk of products through formula optimization.

Key words: class A foam extinguishing agent, zebrafish, acute toxicity, half lethal concentration