Integrating lipids and contaminants in aquatic ecology and ecotoxicology

Heterotrophic organisms in marine and freshwater food webs ingest a wide range of essential and xenobiotic compounds. Essential compounds are physiologically required by consumers, yet cannot be synthesized de novo, or cannot be synthesized in quantities sufficient to meet an organism\u27s need for somatic growth, reproduction, and survival (see Goulden and Place 1990, for daphnids; Tocher 2003, for teleost fishes). For example, some polyunsaturated fatty acids (PUFA) and trace elements such as zinc (Zn), iron (Fe), calcium (Ca) are considered essential, and if inadequate amounts are available in the diet, the health and fitness of an organism can be reduced. Xenobiotic compounds have no physiological value for organisms, but can be accumulated by consumers and can be toxic in cases were concentrations are sufficiently high (Watson et al. - Chap. 4). Xenobiotic compounds include many of the classic contaminants, such as PCBs, DDT, and mercury (Hg), and more recently recognized contaminants, such as estradiol, and can also be accumulated from non-dietary sources. It should be noted that essential compounds can also be toxic if concentrations are high enough or if they are converted to other molecules. For example, it has been suggested that PUFA in diatoms can be converted to unsaturated aldehydes, which reduce egg hatching rates in marine herbivorous copepods (Miralto et al. 1999)