Níveis de ocorrência de Hg total em peixes carnívoros das represas de Barra Bonita e Bariri, em função da variação de parâmetros biológicos e da presença de selênio.
Abstract
The Barra Bonita and Bariri reservoirs, Medium river Tietê, São Paulo, Brazil, are
used with several purposes as transport, provisioning, electric power generation,
professional fishery and leisure. The region is surrounded by an industrial
developed pole, receiving sewer of domestic and industrial origin, as well as the
effluents of agricultural activities. Not only the pollution for organic pollutants, but
also for the inorganic ones, among them heavy metals, are getting the civil society
and the scientific community attention, because they mean a hopeless loss of the
natural resources. Among heavy metals, mercury is considered one of the more
toxics, causing neurological, reproductive and teratogenic disturbances. Before this
panorama and because it was certain the mercury presence in these aquatic
ecosystems, the present work had as objective quantifies the tenor of Hg in fish,
water and sediment. For that, two carnivorous fish species were analyzed Hoplias
malabaricus and Serrasalmus spilopleura for a period of one year. Along two
years, water and bottom sediment were collected in four different times, in an
attempt of determining the seasonal variation. Limnologic parameters and
selenium concentration were quantified in an attempt of determining their influence
on Hg availability. The medium levels of Hg found in the fish were below the
established limit for the human consumption (0.5 mg Hg.Kg-1), however, it was
above that established for the conservation of the aquatic life (0.01 mg Hg.kg-1),
and they can represent a risk, due to the bioaccumulation. It was not possible to
establish a correlation among Hg and Se present in both fish species. The values
of Hg and Se in the water stayed below the detection limit of the method (2.0 ng
Hg.L-1 and 5.0 ng Se.L-1). In relation to the sediment, although, only in some points
of the two reservoirs Hg has state above the allowed limit (1.0 mg Hg.kg-1), the fact
should be analyzed with caution, once the sediment is accumulative and potential
source of pollutants. In this way, public politics seeking the permanent water quality
monitoring, as well as the prohibition of antropic pollutant activities, are essential
for balance and sustainability maintenance of Barra Bonita and Bariri reservoirs.