Removal Efficiencies Of Clays Modified By Different Kinds Of Surfactants Against Chattonella Marina

The harmful algal blooms (HABs) frequently occur and result in the serve mortality of fishes and invertebrates, and harm to the cultivation and ecological system in South Chin Sea. It is urgently needed to investigate how to control HABs effectively. However, progress is still slow in developing effective and economic controlling strategies. Many studies on controlling or inhibiting the growth of HABs species have been conducted. Of them, natural clays attracted much attention due to its non-toxic and friendly to environment.In this paper, to explore the new modified clays with excellent algae removal efficiencies, clays were modified by three kinds of surfactants such single-chain quaternary ammonium salts, single-stranded quarter of phosphate and Gemini surfactants with different structures. The removal efficiencies of the modified clays against Chattonella marina, a typical HABs alga in China were observed. The toxicities of the modified clays with high removal efficiency on Brachydanio rerio, Miona mongolica Daddy and Litopenaeus vannamei were evaluated.The clays modified by tetradecyl quaternary phosphonium were shown to have the highest removal efficiency, followed by ones with decyl, dodecy and cetyl quaternary phosphonium. The clays modified by tetradecyl quaternary ammonium with different substituent groups such as trimethyl, dimethyl phenmethyl and dimethyl ethide had similar removal efficiency, suggesting less effect of the substituent groups in quaternary ammonium on the algaecide activity of the modified clays. Among the modified clays assayed, the clays with tributyltin bromide tetradecyl phosphonium and two-brominated ethyl dimethyl tetradecyl ammonium had the highest removal efficiency. The EC50120 of the two modified clays against C. marina was only 6.11 mg/L and 6.13 mg/L, respectively, indicating that these two modified clays could remove the algae effectively under low concentrations. Low toxicities of these two modified clays were shown in the acute toxicity tests of B. rerio. None of the B. rerio were killed in 96 h after exposed to the two modified clay in the concentration of 10～100 mg/L. However, some differences in toxicity to M. mongolica were exited between them. The LC50 in 24 h of clay with tributyltin bromide tetradecyl phosphonium against M. mongolica was above 100 mg/L, while the other one was only 9.37 mg/L. Obviously, clay modified by tributyltin bromide tetradecyl phosphonium was less toxic to M. mongolica than that of modified by two-brominated ethyl dimethyl tetradecyl ammonium. Combining the high removal effectiveness on C. marina and low toxicity to B. rerio and M. mongolica, it was reasonable to consider the clay modified by tributyltin bromide tetradecyl phosphonium a potential algaecide with high effectiveness and low toxicity to fishery.The clays modified by four Gemini surfactants such as ethylene bis(dodecyl dimethyl ammonium chloride) (EDAC), ethylene bis (octadecyl dimethyl ammonium chloride) (EOAC), poly(quaternary ammonium salt)(PQAS) and ethylene bis(dodecyl dimethyl ammonium bromide) (EDAB) were all shown to exhibit high removal efficiencies against C. marina. Among them, the clay modified by EDAB had the highest removal efficiency, with EC50120 of 0.42 mg/L. Simple mixture of EDAB and natural clay did not enhance the removal efficiency of them against C. marina. In contrast, the clay modified by EDAB exhibited higher removal efficiency than EDAB and clay did, with an ideal composition ratio of 15%. At 3 mg/L, removal efficiency of the clay modified with EDAB was above 90%. The LC50 in 48 h of clay with EDAB against B. rerio, juvenile L. vannamei and adult L. vannamei were 25.66, 12.49 and 48.03 mg/L, respectively, suggesting the low toxicity of the modified clay to other aquatic organisms. In addition, EDAB modified clays could reduce the level of soluble nitrogen in water by adsorption. Combining the high removal efficiency on C. marina, low toxicity to B. rerio and L. vannamei, and high adsorption capacity for soluble nitrogen in water, it would probably be reasonable to believe that the clay modified by EDAB should be better a favorable choice to control HABs. However, further studies are awaited to prove the hypothesis we have proposed in the future in an open aqua-ecosystem.