Biologically labile

Phosphate esters have the desirable qualities of both chemical stability (Flynn and Lamb, 1970) and biological lability (Amidon et al., 1977 Amidon, 1981). There is evidence that the soluble phosphate ester is enzymatically hydrolyzed to the active agent in the body (Melby and St. Cyr, 1961 ... 

Moran, M. A., and R. G. Zepp. 1997. Role of photoreactions in the formation of biologically labile compounds from dissolved organic matter. Limnology and Oceanography 42 1307-1316. 

TABLE I Biologically Labile Photoproducts Formed from Freshwater and Marine DOM... 

The second pattern evident in Table II is that the photochemically mediated transfer of carbon into the microbial food web is more pronounced for deep-water marine DOM than for surface water marine DOM. In two studies that explicitly compared relative photoreactivity of surface and deep samples, the biological lability of deep-water DOM was consistently greater after exposure to sunlight, whereas surface waters typically... 

TABLE IV Ecological Significance of Biologically Labile Photoproducts in Surface Waters (A) and on a Depth-Integrated Basis (B)... 

There have been some attempts to find chemical or physical correlates of short-term consumption that can be used as indices of biological lability (Amon et al., 2001). For example, there is indication that bioavailability (i.e., in terms of milligrams bacterial biomass per milligrams of DOC consumed) is correlated to the elemental composition in terms of C, N, H, and O, to the aliphatic contents, and to the overall degree of reduction of the DOM (Sun et al., 1997 Hopkinson et al., 1998 Hunt et al., 1999). However, there is still no general index that is applicable to all different aquatic systems, and it is unlikely that a single index will be able to account for variation in the multiple factors that simultaneously determine DOM... 

Figure 6. Seasonal changes estimated for potential biologically labile photoproduct production from terrestrially-derived CDOM at various latitudes in the Northern Hemisphere [67].

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