VERTIMAR-2005
Symposium on Marine Accidental Oil Spills
Variation in the concentration of polycyclic aromatic
hydrocarbons (PAHs) in mussels (Mytilus galloprovincialis) at
the Galician Coast after the Prestige oil spill
Óscar NIETO1, Janire ABOIGOR1, Liliana SACO-ÁLVAREZ2 and Ricardo BEIRAS2
1Departamento
de Química Analítica e Alimentaria
de Ecoloxía e Bioloxía Animal
Facultade de Ciencias do Mar. Universidade de Vigo. E-36200 Vigo, Galicia, Spain
2Departamento
ABSTRACT In the present work, the temporal variation of the PAH levels in wild mussel (Mytilus galloprovincialis),
was studied in three sampling sites of the Galician coast between the Rías of Arousa and Muros, which were
dramatically affected by the Prestige large oil spill. The concentrations of the sum of the 16 PAHs determined are
between 2.5 and 5.9 µg g-1 (dry weight) in the subsequent days to the oil spill and they decrease down to 0.13 on
October 2003. As expected, the PAH concentrations found in the mussels and water samples are in agreement to the
impact of the oil spillage at the sampling locations. A good relation between parent PAHs accumulated in the mussels
has been calculated in order to provide an indication of hydrocarbon pollution and was obtained when ∑PAH is
represented versus the ∑LPAH/∑HPAH ratio. The depuration of individual PAHs by the mussels was fitted to an
exponential model, two different values of r have been found depending on the PAH concentration.
1. INTRODUCTION
On November 16th, the oil slick from the tanker Prestige reached the coast, affecting a
coastline zone between cape Corrubedo and Ferrol. In that moment, we started sampling a
small area near cape Corrubedo, between the rías of Muros and Arousa and collected mussel
(Mytilus galloprovincialis) in order to follow up the impact of the fuel. During the first days of
December, a second black tide, as a consequence of the tanker reached the south of the
Galician coast, including the stations we had previously considered as non polluted ones.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous components in the marine
environment. Several tanker accidents occurred in the Galician coast before the Prestige, such
as Andros Fortune, Polycommander, Urquiola, Andros Patria and Aegean Sea, but the studies
on PAHs were only performed after the oil spill of the last one (Porte et al. 2000). In this work, a
study of the temporary variation of the HAP content in mussel (Mytilus galloprovincialis) is
presented.
2. RESULTS AND DISCUSSION
Figure 1. Variation of the total hydrocarbon concentration (except Nap, Ace and Flu) in
mussel samples over time.
VERTIMAR-2005
Symposium on Marine Accidental Oil Spills
The sum of the concentrations of individual PAHs determined by HPLC in the mussels is
represented versus time in Figure 1. The hydrocarbon contents found at M1 since the first
sampling day are exorbitant and a maximum value (about 5.9 mg Kg-1 d.w.) is detected on
January 3th 2003. The concentrations are higher than those previously reported (Porte et al
2000, Baumard et al. 1999) but for one case after the Exxon Valdez oil spill (about 8 mg Kg -1,
d.w.; see Carls et al. 2001). In a beginning, M2 was chosen as an apparently non-polluted area,
(0.3 mg Kg-1 d.w. on November 2002). However, there is a drastic increase after the second oil
slick reached the coast. As reference values of a non polluted area, those obtained from
mussels collected close to the mouth of the Ría of Pontevedra on February 2002, have been
used (dashed lines). In all cases, the concentrations decline down to background values from
April-June 2003 onwards.
Figure 2. Plot of the total PAH content (∑PAH) versus the ∑LPAH/∑HPAH ratio. The
hydrocarbons used for the sum of ∑PAH, ∑LPAH and ∑HPAH are in the text.
There is no uncertainty about the source of hydrocarbons, but a relation between parent
PAHs is calculated to test the degree of hydrocarbon pollution as that reported by De Luca et al.
(2004), where the total PAH content (∑PAH) is represented versus the ∑LPAH/∑HPAH ratio
(∑LPAH = Nap + Ace + Flu + Phe + Ant, and ∑HPAH = Fla + Pyr + BaA + Chr + BbF + BkF +
BeP + BaP + BghiP + DahA + Ipy). The results are shown in Figure 2 and all the points in the
plot can be adjusted as ∑PAH = 6.82 exp(-6.51 ∑LPAH/∑HPAH); r = 0.89
Most of the points can be gathered into two well defined areas: ∑PAH > 0.8 mg Kg -1 (d.w.)
and ∑LPAH/ ∑HPAH < 0.6 correspond to a contaminated zone; ∑PAH < 0.8 mg Kg-1
(d.w.) and a ∑LPAH/ ∑HPAH > 0.6 correspond to a non polluted one; and the rest of the
points can be considered as alert values.
The decrease in the hydrocarbon concentration follows an exponential curve that can be
adjusted to Ct = C0 exp(-rt) (Farrington et al. 1982); where Ct is the concentration of a parent
hydrocarbon at a given time t (days); C0 is the maximum concentration of that PAH (ng g-1, d.w.)
and r is the depuration rate. The values of r are calculated for each PAH and, in most cases, the
data show two phases of depuration with different slopes. The results suggest the existence of
two depuration mechanisms that do not depend on their nature but on their concentrations.
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