Polycyclic aromatic hydrocarbons (PAHs) are widely recognised as harmful, persistent
organic pollutants, whilst surfactants are more easily degraded but their ubiquitous use
both domestically and industrially ensures their presence in natural waters. Owing to
both their hydrophobic and hydrophilic properties, surfactants are capable of both
adsolubilisation and solubilisation of co-contaminants, hence, their presence in natural
waters is considered extremely significant. The purpose of this research was to
determine how surfactants and PAHs influence each other in estuaries where both are
co-disposed. This study is the first to employ environmentally realistic concentrations of
surfactants and to use natural particles in order to determine how changes in surfactant
behaviour impinge on the sorption of a representative PAH to sediment.
The experimental method employed involved tracing the solubility and sorption of a
'''C-labelled PAH (phenanthrene) in the presence of representative surfactants from the
three main groups, i.e., anionic, nonionic and cationic. Initially the four compounds
were examined in isolation at two temperatures (8°C and 20°C), salinities and particle
concentrations. The next stage involved incorporating each surfactant with
phenanthrene in the same experiment and repeating the range of variables.
Solubility and adsorption of phenanthrene in the presence of Triton X-100, sodium
dodecyl sulphate (SDS) or hexadecyltrimethylammonium iodide (HDTMA) proved to
be highly complex. The adsorption, expressed as a Freundlich coefficient, KF was
generally nonlinear and varied according to surfactant type, salinity, temperature, and
contact sequence. The overriding influence, however, was sediment particulate matter
(SPM) concentration. On some occasions the surfactants in isolation displayed unusual
particle concentration effects (PCE), such as an increase of surfactant in the aqueous
phase as the SPM concentration increased. Despite this, they all generally exaggerate
the more typical PCE displayed by phenanthrene, where the particle-water partition
coefficient is reduced as particle concentration increases. This effect is then modified by
temperature and contact sequence, which has important environmental implications with
regard to removal or release of compounds stored within sediments. However, overall,
at environmentally relevant concentrations, the surfactants appear to enhance sorption,
rather than solubility, with HDTMA the most effective surfactant at removing
phenanthrene from the aqueous phase.BMT Marine Information Systems Limited
Southampton
and
AstraZeneca
Brixha
