Bioconcentration factor hydrophobicity cutoff: an artificial phenomenon reconstructed

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Bioconcentration Studies

Background:

• A hydrophobicity cutoff in bioconcentration factor (BCF) measurements for highly hydrophobic chemicals (log Kow > 5-6) is debated.
• This cutoff may stem from measurement artifacts or reduced membrane permeation of large molecules.
• The validity of current risk assessment models incorporating a BCF cutoff is questioned.

Purpose of the Study:

• To investigate the existence of a hydrophobicity cutoff for highly hydrophobic organic chemicals.
• To identify and explain artifacts affecting BCF measurements.
• To propose revisions for BCF measurement techniques and risk assessment strategies.

Main Methods:

• Uptake of polycyclic aromatic hydrocarbons (PAHs) in Lumbriculus variegatus was measured.
• BCFs were determined using traditional batch uptake kinetics and alternative methods (SPME, POM-SPE, field exposures, dead worms, liposomes).
• Comparison of BCFs across different measurement approaches to identify discrepancies.

Main Results:

• A hydrophobicity cutoff was observed only with traditional BCF measurement approaches.
• Alternative methods did not show a hydrophobicity cutoff for compounds with log Kow up to 7.5.
• Artifacts, including third-phase effects and nonequilibrium conditions, were identified as causes for the observed cutoff in traditional methods.

Conclusions:

• The hydrophobicity cutoff effect in BCF measurements is likely an artifact, not a true biological limitation.
• Current BCF measurement techniques and risk assessment strategies for very hydrophobic chemicals require revision.
• Accurate assessment of bioconcentration for highly hydrophobic compounds necessitates improved methodologies that avoid artifacts.