Fate of Model Xenobiotics in Calcareous Marine Algae!

Uptake, depuration, and metabolism ofp-nitroanisole (PNA) and p-nitrophenol (PNP) were investigated in Halim eda, Padina, and Porolithon species, all of which are calcareous marine algae found in tropical waters . The algae were exposed to filtered seawater solutions of either PNA or PNP in a static system for 24 hr (uptake period), then placed in clean water and allowed to release absorbed chemical and possible metabolites for 24 hr (depuration period). Concentrations of the chemicals were monitored spectrophotometrically, and the water at the end of uptake and depuration was extracted onto a column of Amberlite XAD-4 resin, eluted sequentially with methylene chloride and methanol , and analyzed for metabolites by high-pressure liquid chromatography (HPLC). Results showed that the algae absorb PNA but not PNP. There was no indication that they were capable of metabolizing PNA, except inconsistently, to PNP. However, half of the absorbed PNA remained unaccounted for, and may either have been metabolized to undetected metabolites or bound to tissue macromolecules. Because man y of these algae live on the shallow reef flats, they are likely to be exposed to xenobiotics introduced either indirectly in shoreline runoff or directly as chemical spills (pesticides, oil, etc.) on the reef. Although there have been studies on the ecology, growth , and intermediary metabolism of these algae (Hillis-Colinvaux 1980, Johansen 1981), there seem to be no reports on their ability to metabolize xenobiotic compounds. Xenobiotic metabolism consists of primary reactions (oxidation, reduction, and hydrolysis) , and secondary reactions (conjugation to polar groups), which render the chemical more water-soluble (polar) and thus easier to excrete. Because it is moderately fat-soluble and it can be modified by many metabolic reactions , p-nitroanisole (PNA) is a good model pollutant; it can be demethylated via oxidation to form p-nitrophenol (PNP), ring oxidized at the 2-position to the nitrocatechol, or reduced to form an amine (Figure 1). In addition , the analytical techniques to detect and measure PNA and many possible metabolites have already been developed (Foster and Crosby 1986). The purpose of this research was to investigate the uptake, depuration, and biodegradation of the model compounds in three types of