5.10.1 Potential Environmental Effects
22.214.171.124 Algal Toxins
Known toxin-producing strains are not likely to be used in algal biofuel production systems. Indeed, many species have food grade status or are being used as feed in aquaculture. However, some species regarded as benign may in fact produce toxins previously unknown. Examples of these include newly discovered euglenoid toxins (Zimba et al., 2010) and free radical toxins (Moeller et al., 2007). In addition, contaminating toxin-producing algae and cyanobacteria could potentially colonize production systems, especially open ponds.
Human toxins that are produced by cyanobacteria have been found in freshwater, marine, and estuarine organisms and include hepatotoxins, cytotoxins, dermatotoxins, and neurotoxins among others (Smith et al., 2008). Ecotoxicity from algal toxins is observed in fish (Zimba et al., 2001b), shellfish (Lance et al., 2011), or invertebrate herbivores such as Daphnia and shrimp (Zimba et al., 2006; Sarnelle, 2010). Toxins can affect viability, growth, and fecundity of many organisms (Plumley, 1997).
The chemical structures of freshwater toxins are probably more diverse than those of marine toxins, including alkaloids, phosphate esters, macrolides, chlorinated diaryllactones, and penta- and hepta-peptides (Rouhiainen et al., 1995; Smith et al., 2008). Species of toxin-producing algae in the divisions Euglenophyceae, Bacillariophyceae, Dinophyceae, Haptophyceae, and Raphidophyceae have been documented. Some cyanobacteria also are producers of toxins and probably are responsible for the production of most freshwater algal toxins from harmful algal blooms (Plumley, 1997). Toxicity of some compounds can exceed that of curare (Zimba et al., 2001a). Irritants and allergens also are produced by certain algae. Toxin production in some cyanobacteria is influenced by environmental variables and competition (Moeller et al., 2007; Briand et al., 2008), though the physiological and ecological causes of toxin production are largely unknown (Paerl and Millie, 1996; Carrick, 2011). Harmful blooms of toxin-producing algae are not the sole source of algal toxins, nor are algal toxins always associated with blooms (Plumley, 1997). Moreover, blooms cannot be predicted with accuracy in natural environments (Carrick, 2011), and this likely applies to open biofuel cultivation systems as well.
Both freshwater and marine forms of toxin-producing algae could colonize production systems. The current state of knowledge about phytoplankton community composition is not sufficient to predict whether toxin-producing strains could invade and bloom in algal biofuel production systems, even if these systems are seeded either initially or continuously with non-toxigenic algal strains.
Compounds presently not known to be harmful because of their presence in low concentrations in small-scale, low-intensity algal biomass production may have harmful impacts when concentrated 100,000 times during the harvesting and drying phases. Concentrated cultivation methods may lead to the identification of previously unknown toxic material (Moeller et al., 2007; Zimba et al., 2010). If the lipid-extracted algae are to be used in value-added coproducts, the quality of those products would have to be monitored.
The outdoor open-pond production systems likely will develop diverse algal populations (Smith et al., 2010). Monitoring algal composition is critical to maintaining desired