Learning from the Eco-Toxicology of Fire-Fighting Foams in Aquatic Organisms: Altered Eco-Toxicity of Sodium Alkyl Sulfonates on Green Paramecia and Medaka Fish Maintained in Different Waters

A variety of ciliated and flagellated protozoan species have been used as bio-indicators of the eco-toxic impacts of polluting chemicals, especially in aquatic environments such as rivers, ponds, lakes, and wetlands. To date, both the short-term and long-term impacts of fire-fighting foams (FFFs) in aquatic (freshwater environment) and semi-aquatic (wetland) ecosystems have been assessed in laboratory-scale model assays and in biotope-based assays. Little attention has been given to the fact that water qualities, such as hardness, drastically alter the toxic actions of various chemicals against living aquatic organisms including fishes, algae, and other microbes, suggesting that the laboratory water often employed in toxicity assays for fishes and microorganisms might not reflect the actual impact of chemicals in the ecosystem. Therefore, for examining the toxicity of certain chemicals (chiefly detergent-based and soap-based FFFs) in aquatic organisms, we have previously proposed that a series of simple eco-toxicity tests using natural waters sampled from the natural organism's habitats or blends of min-eralcontaining water preparations mimicking the natural habitat waters be used in addition to tests in standard laboratory waters. Based on the knowledge of the eco-toxicity of FFFs obtained through past studies using model aquatic organisms such as green paramecia (Paramecium bursaria), we conducted a study aiming to uncover the toxic mechanism of sodium alkyl sulfonates, a series of synthetic detergents known as SAS, using a strain of P. bursaria originally sampled from a river, both in laboratory water and habitat river water (river water from where P. bursaria was collected; HRW). Here, we employed P. bursaria maintained in both a natural HRW-based assay medium and an ultrapure water-based low-mineral standard culturing medium for comparing the apparent toxicity of SAS. Data strongly suggested that the toxicities of most SAS detergents (alkyl chains shorter than 9 carbons or longer than 14 carbons) are mini-mized in the mineral-rich HRW compared to the commonly used UPW-based low-mineral ciliateculturing conditions. The toxicity of SAS members with moderate chain lengths, such as sodium dodecan sulfonate, tended to be minimized with elevated mineral content. A similar tendency was also observed in medaka fish, a tiny model fish.