and frozen pending column preparation. The oiled gravels were
inserted (12 kg per column) into 1 m high polypropylene columns
(110 mm in diameter), that is one column per treatment. Each oil
concentration and control treatment consisted of 5 replicate glass
petri dishes (diameter 50 mm) containing 20 eggs. Particle-filtered
(60 m) and UV treated seawater (960 ml/min) at ambient sea
water temperature (Fig. 1) were pumped upwards through the
columns, extracting 100 (±10) ml/min of the WSF into each of
the experimental dishes (pseudoreplicates). Each dish was placed
into a mesh (500 m) cylinder to avoid any loss of eggs in the
flow-through system. The control dishes received water percolated
through a column containing clean gravel. To ensure the
volatilization of BTEX compounds (benzene, toluene, ethylbenzene,
and xylene) and an absence of particulate oil, water was pumped
through the columns for 48 h before the exposure of the eggs
started. In the period 15th of May–21th of May (day 26–32) the
set-up was changed from a flow through system to a semi static
system to avoid loss of hatched larvae. Exposure waters were then
collected from each column, and 10 ml was added to each dish and
changed every 24-h. Water samples for PAH quantification were
taken from the outlet of each column once per week and frozen at
−20 ◦C until analysis.