Time-dependent bioaccumulation

The length of the food chain has the largest effect on the observed accumulation of PCBs in top predators [268]. However, one of the more sensitive aspects of trophic transfer in food webs is the initial uptake of PCBs into the primary trophic level, phytoplankton [263]. The BCF from water to phytoplankton is approximately 105 -106, and subsequent BMFs to higher trophic levels are on the order of two to five. Due to the life cycle of most phytoplankton, their rate of growth is on the same order as their rate of uptake of PCBs, thus making their uptake very time-dependent [227,269-271]. Bioaccumulation into top predators will be greater if phytoplankton have a chance... 

Historically, organic environmental pollutants were hydrophobic, often persistent, neutral compounds. As a consequence, these substances were readily sorbed by particles and soluble in lipids. In modern times, efforts have been made to make xenobiotics more hydrophilic - often by including ionisable substituents. Presumably, these functional groups would render the compound less bioaccumulative. In particular, many pesticides and pharmaceuticals contain acidic or basic functions. However, studies on the fate and effect of organic environmental pollutants focus mainly on the neutral species [1], In the past, uptake into cells and sorption to biological membranes were often assumed to be only dependent on the neutral species. More recent studies that are reviewed in this chapter show that the ionic organic species play a role both for toxic effects and sorption of compounds to membranes. 

Diphenhydramine, diltiazem, carbamazepine and norfluoxetine have been reported simultaneously in the same wild fish [107]. Moreover, diclofenac was found accumulating in vultures [119], fluoxetine, sertraline and the SSRl metabolites norfluoxetine and desmethylsertraUne were detected in fish [120]. Diclofenac bioaccumulation factors were 10-2,700 in the liver of fish and 5-1,000 in the kidney, depending on exposure concentrations [40, 121]. Gemfibrozil occurred in blood plasma of goldfish after exposure over 14 days at 113 times higher levels than in water [40]. 

Fig. 4. Time and exposure concentration dependent concentrations in fish in addition to the lethal body burden (horizontal solid line) for 1,2,3-trichlorobenzene. The dotted lines are theoretical curves calculated with a bioaccumulation model. Exposure concentrations are 55.9 pmol 1 (I), 3.78 pmol (II), and 1.92 pmol (III). The symbols represent the mean of the internal effect concentrations of ten fish [9], reproduced with permission...

Cyclodienes (chlordane, aldrin, dieldrin, heptachlor, endrin, mirex, endosulfan, chlordecone). This new class of pesticides appeared on the scene following World War II. Most of them are very stable to sunlight and persistent in soil and they were used to control termites and other insects. Their effectiveness leads to insect resistance and bioaccumulation in the food chain and for these reasons their use was banned between 1984 and 1988. These compounds affect the CNS in the same way, causing tremors, convulsions, and prostration to the maximum extent, depending on the rate and time of exposure. 

Bioconcentration refers to the passive partitioning of a xenobiotic between an abiotic environmental medium and a living organism. Bioaccumulation desaibes the uptake and retention of a xenobiotic from all sources, biotic (prey) as well as abiotic. Bioaccumulation depends on the same phenomenon as bioconcentration The rate at which an organism takes up a xenobiotic exceeds the rate at which the organism is able to eliminate it As a result, more chemical enters the body than leaves it per unit time. 

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