Removal of harmful algal cells (Karenia brevis) and toxins from seawater culture by clay flocculation

Abstract

Harmful algal blooms (HABs) occur worldwide causing serious threat to marine life, and to public health through seafood-borne illnesses and exposure to toxin-containing marine aerosol. This study was undertaken to assess the ability of phosphatic clay to remove the toxic dinoflagellate, Karenia brevis, and the potent neurotoxins (brevetoxins) produced by this species. Results showed that the addition of an aqueous slurry of 0.75 g (dry weight) clay to 3 l of K. brevis culture, containing 5 × 10 6 and 10 × 10 6 cells/l, removed 97 ± 4% of brevetoxins from the water column within 4 h after the addition of clay. Clay flocculation of extra-cellular brevetoxins, released from cells ruptured (lyzed) by ultrasonication, removed 70 ± 10% of the toxins. Addition of the chemical flocculant, polyaluminum chloride (PAC), removed all of the extra-cellular toxins. A 14 day study was undertaken to observe the fate of brevetoxins associated with clay flocculation of viable K. brevis cells. At 24 h following the clay addition, 90 ± 18% of the toxins were removed from the water column, along with 85 ± 4% of the cells. The toxin content of clay diminished from 208 ± 13 g at Day 1, to 121 ± 21 g at Day 14, indicating that the phosphatic clay retained about 58% of the toxins throughout the 14-day period. These studies showed the utility of natural clay as a means of reducing adverse effects from HABs, including removal of dissolved toxins, in the water column, although considerable work clearly remains before this approach can be used on natural blooms in open waters.

A marine algicidal actinomycete and its active substance against the harmful algal bloom species Phaeocystis globosa

“…These strategies can be summarized as physical methods (e.g., clays and flocculants) (Pan et al 2006;Pierce et al 2004;Sengco et al 2001Sengco et al , 2005, chemical methods (e.g., copper sulfate, surfactants, and sodium hypochlorite) (Baek et al 2003;Jeong et al 2002;Sun et al 2004), and biological methods (e.g., algicidal bacteria, algicidal viruses, and plankton grazers) (Hare et al 2005;Kim et al 2009;Mitra and Flynn 2006). However, the use of physical and chemical methods in aquatic ecosystems is potentially dangerous; their high cost, secondary pollution effects, and impracticability also limit their application (Anderson 1997).…”

Removal of cyanobacterial blooms in Taihu Lake using local soils II. Effective removal of Microcystis aeruginosa using local soils and sediments modified by chitosan

“…However, one of the main problems concerning the application of clays is the unrealistically high clay loadings required. It is reported that the effective clay loadings were approximately in the range of 0.25e2.5 g/L (Pierce et al, 2004;Sengco et al, 2001;Yu et al, 1994aYu et al, ,b, 1995, although for very few clays the loading could be as low as 0.1 g/L (Pan et al, 2003(Pan et al, , 2006a. Another major problem is that the efficiency of clay flocculation decreases dramatically as salinity decreases (Han and Kim, 2001;Pan et al, 2006b), making it difficult to apply normal clay technique to control cyanobacterial blooms in lakes.…”

Harmful Marine Phytoplankton Community in Shirazi Creek, Kenya

“…The observed low cell densities of these harmful algal species could be attributed to the creek's altered photochemistry brought about by the high turbidity levels caused by the Ramisi river inflow and tidal movements that resulting into sediment flocculation, flushing out and sinking of attached algal cells (Pierce et al, 2004). The wide distribution of the observed harmful algal species in this study (but in low cell densities) could be explained by the fact that these species are less affected by coastal nutrient enrichments (Hansen et al 2001b).…”