It is well known that anthropogenic contaminants accumulate along the food chain, but it is less commonly known that natural contaminants may do the same. An example is the contamination of filter feeders (bivalves, fish, etc.) with algal toxins. As a result of accumulation in higher trophic levels, algal toxins may also be present in other nonefilter-feeding organisms. During (harmful) algal blooms, seawater can contain up to several million algae per liter. In the majority of cases, marine biotoxins are produced by eukaryotic organisms, especially marine dinoflagellates and diatoms. Cyanobacteria (formerly known as blue-green algae) are the main source of phycotoxins in limnic water bodies. Some of the different clinical types of algae-related poisonings that have attracted scientific attention in recent years include paralytic shellfish poisoning (PSP), diarrheic shellfish poisoning (DSP), amnesic shellfish poisoning (ASP), and ciguatera fish poisoning (CFP). The increasing frequency of harmful algal blooms (HABs) in marine, brackish, and freshwater environments and the worldwide demand for tropical fish necessitate the monitoring of HAB population dynamics and toxin concentrations. The assessment of the risks of human exposure to phycotoxins and the analysis of aquatic food for phycotoxins are important tasks that must be conducted according to international regulations and in compliance with legal restrictions. Bioassays have been commonly applied for the determination of phycotoxins; however, they fail to provide important information about the chemical nature as well as the quantities of the causative toxins. Further questions concerning the relevance of animal experiments (e.g., with rodents) arise in the context of the reliability of those toxicity assays for humans (even when safety factors are considered), not forgetting the ethical aspects of unavoidable animal cruelty of such bioassays. Therefore research into new analytical methods to allow the reliable determination of phycotoxins has been ongoing in the
recent past. Such methods must also be rapid to perform. In this context, liquid chromatography-mass spectrometry (LC-MS) methods allow effective food control and monitoring of phytoplankton in terms of the unambiguous and sensitive determination of phycotoxins in compliance with international legislation.