R. H. Wijffels and M. J. Barbosa's Perspective in the special section on Scaling Up Alternative Energy ("An outlook on microalgal biofuels," 13 August 2010, p. 796) emphasizes that economically feasible production of microalgae for biofuel will only be achieved if co-products are also explored. Wijffels and Barbosa estimated that plenty of protein would be a co-product of microalgal biofuels. In the Perspective, retaining the functionality of co-products was referenced. However, the safety of co-products was ignored.

Microalgal biofuel co-products should not be recommended for use unless both nutritional quality and toxicological safety have been verified. High nucleic acid content of microalgal biofuel co-products may elevate the uric acid level of serum, and hence increase the risk of gout in humans. Another problem is that the high-density culture of microalgae in natural conditions may induce production of secondary metabolites, such as toxins from algal blooms, and potentially threaten human health. Environmental and biological contaminants in the process of microalgal mass-culture and separation of triglycerides and co-products can limit the use of microalgal biofuel co-products as animal feed and food. Environmental contaminants mainly include heavy metals and organic compounds; biological contaminants include alien microalgae, fungi, insects, and bacteria.

To ensure the safety of microalgal biofuels co-products, we should cautiously choose culture locations and strictly control production processes. A few microalgal strains have been successfully commercially applied, but the scale of biofuel's production system is much larger than the current system. Detailed safety criteria for culture treatment and application will be needed if one ideal microalgal strain is to be used as food and animal feed.