The fields surrounding the complex are mostly
used for agricultural and livestock purposes. The predominant vegetation
includes ryegrass and mustard greens. The ECC dates back to the
1950s and among other industrial units it includes a chlor-alkali plant
with production of chlorine and sodium hydroxide from rock salt and
which used electrolytic cellswith mercury cathodes for several decades
(Costa and Jesus-Rydin, 2001). Since the 1950s and until the late 1970s,
liquid effluents from the Chemical Complex were discharged into the
“Esteiro de Estarreja”, which is a river branch of a nearby lagoon
(“Ria de Aveiro”), through open streams that crossed the surrounding
agricultural fields, such as “Vala de S. Filipe” (Fig. 1). In 1986 the plant
consumed 28 ton/year of Hg as a raw material and it was estimated
that around 12% of annual consumption of Hg was released to the
atmosphere (Rodrigues et al., 2006).