The Study Of Modified Clays Influence On Environmental Quality In Red Tide Control

The primary objective of this study was to determine the environmental influences of clayflocculation in red tide blooms through laboratory test. The result as follows: When modifiedclay to control algae bloom, those water quality parameters were controlled or smoothed, suchas Dissolved Oxygen (DO), Chemical Oxygen Demand (COD) and pH. Moreover those clayscould absorp the eutrophic salt, especially phosphate. When phosphorus concentration rangedfrom 0.1μmol/mL to 0.3 μmol/mL, the phosphate adsorption amounts increased on organicmodified clays. The phosphate adsorption ability of different organic clays is: modifiedclayⅠ> modified clayⅡ> modified clayⅢ> unmodified clay. However, there is no obviousremoval ability of nitrate. To study the absorption-desorption effects on ecology, wesimulated the phosphate desorption and the consequent effect to the growth of Heterosigmaakashiwo and Prorocentrum donghaiense., the result show that d modified clay could holdmore phosphate on itself, which will be helpful to mitigate eutrophication. Moreover,phosphate desorption in sea water could not afford phytoplankton growth. Inorganic modifiedclay is similar to the organic clays of the ability on nitrates. Mitigation or control the red tid byorganic/ inorganic modified clays could enchance the water quality parameters.Then modified clays were tested for the potential environmental impact on benthicorganism. Laboratory experiments were conducted to investigate the survival and physiologicalchanges of infant oyster (Crassostrea gigas). LC50 (96h ) of organic and inorganic modifiedclay are 4.62 g/L和2.67g/L,which is higher than clay concentration in practical red tidmanagment. The percentage survivals of oysters,Filtering rate and growth in modified clays atpractical concentration are almost equal to those in control during acute and chronic toxicity. in56 days erposure in 0.10 g /L organic or inorganic modified clays. Results of TransmissionElectron microscopy showed that both clays have no physical hurt to the gill and digestivegland of infant oyster after chronic test. Clay modification was not acutely or chronically toxicin most cases.Finally, because paralytic Shellfish Poisoning (PSP) is the most serious and widespreadshellfish toxicity, this study was undertaken to assess the ability of phosphatic clay to removethe toxic dinoflagellate, A. tamarense, which produce PSP toxins. Results showed that theaddition of aqueous slurry can reduce A. tamarense and PSP from seawater. In clay sedimentwhen upon rupture or lysing of the cells, the toxins can be released into the water column asextracelluar toxin, however, it has little effect on oyster compared with control for toxinsdiluted in seawater after cell break, and oyster get lease toxicity form gulf or rupture the PSP inseawater than algae directly. Moreover, laboratory tests simulated the toxicity to C. gigas byclay flocculation of the toxic dinoflagellate, A. tamarense (ATHK), Heterosigma akashiwo andProrocentrum donghaiense. The result suggests that clay flocculation of algae cell will increasethe survival rate of infant oyster compared with untreated blooms. Therefore, modified clayshave prospective future in control harmful algal blooms as emergency methods.