Environmental Engineering Reference
In-Depth Information
Heavy metals
Heavy metals are considered very important and highly toxic pollutants
in the various environmental departments. The metals that have received
more attention are Hg, Cd, and Pb, because of their highly toxic properties
and their effects on the environment and the living organisms. Thousand
of tons of these non essential and some essential elements have been input
to the environment from anthropogenic sources: Pb: 450, Zn: 320, Ni: 47,
Cu: 56, Cd: 7.5 (thousand tn yr
-1
). Atmospheric and river inputs, dredging
spoil, direct discharges, industrial dumping and sewage sludge are some
of the important contributors to metal pollution, which lead to the release
of metals to the marine environment.
In surface and ground water, sediment and air, bioavailability of
pollutants is a complex function of many factors including total concentration
and speciation (physical-chemical forms) of metals, mineralogy, pH, redox
potential, temperature and total organic content (both particulate and
dissolved fractions). Many of these factors vary seasonally and temporally,
and most factors are interrelated. Consequently, changing one factor may
affect several others. In addition, generally poorly understood biological
factors seem to strongly infl uence bioaccumulation of metals and severely
inhibit prediction of metal bioavailability (Luoma 1989). The factors affecting
bioaccumulation and bioavailability of metals jointly with the climate
change, that is one of the most signifi cant threats to global ecosystems and
biodiversity (King 2004, Thomas et al. 2004, MEA 2005), are the phenomena
to which we must pay more attention when studying trends in global
distribution and concentration of pollutants. In this sense it is worth pointing
out that the increase in global temperature between 1900 and 2000 was
the largest for any century during the past 1000 years (Huntley et al. 2006,
Osborn and Briffa 2006, IPCC 2007); even if greenhouse and other gaseous
emissions do not increase further, this warming is expected to continue
(Meehl et al. 2005). There is compelling evidence that animals and plants
have been affected by recent global changes in temperature (Walther et
al. 2002, Parmesan and Yohe 2003), potentially leading to extinction of
species in a wide range of taxa (Thomas et al. 2004), so impacts are harder
to predict.
The results of the FD of Hg (µg/g dw) in liver of
Tursiops truncatus
from Mediterranean Sea (including Adriatic and Ligurian Sea, Fig. 1; Table
1) are in agreement with the trend found by Kakuschke and Prange (2007)
where a fall in the concentration of Hg for 1994 to 1999 was observed
(FD=1.8; Table 1) and for 1999 and 2002 Hg concentration remained constant
(FD = 0.1). This trend was followed by a sustained decrease in concentration
up to 2009 (FD = 5.7) in contrast to the fi ndings of Kakuschke and Prange
(2007). The general Hg trend for the Mediterranean Sea—for 1994 to 2009—
