Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 281

1.4

1.2

Sandy sediments
Predicted as
sandy sediments
Silt-clay sediments
Modified

1

0.8

0.6

0.4

0.2

0

0 1 2 3 4 5

Ignition loss (%)

FIGURE 8.7
Conversion of sulide concentrations from sandy sediments to the pore mud water. (Data from Fukue, M.
et al., Evaluation of adverse effects of anoxic sediments on aestivationg sand lance [ Ammodytes personatus ],
Contaminated Sediments, 5th Volume: Restoration of Aquatic Environment, STP 1554, ASTM, pp. 159-174, 2012a.)

8.4.5 Heavy Metals

Many heavy metals are trace metals. These are metals that exist in extremely small quan-
tities and are almost at the molecular level. They reside in, or are present in, animal and
plant cells and tissue and are a necessary part of good nutrition, as shown, for example,
in Table 8.3. Because excess intake of heavy metals may cause damage to human health,
it is necessary to take into consideration the background concentrations in sediments in
structuring safe limits for ingestion of aquatic species. We deine the background concen-
trations (values) as the concentrations of substances under natural condition without any
signiicant input or effect from human activities.
Background values of metals were found to agree well with average values for gneisses
rocks (Carral et al., 1995). However, the background values for copper, zinc, lead, and cobalt
do not necessarily agree with previously obtained values. Various techniques have been
used to reduce data scattering and to allow for a more accurate statement of background
values. Fukue et al . (1999) used carbonates as the normalizing substance in their measure-
ments. Cobelo-García and Prego (2003) obtained the baseline relationships between the
concentration of iron and contaminant, whereas Din (1992), Cortesäo and Vale (1995), and
Santschi et al. (2001) used aluminum to normalize heavy metals. Titan has also been used
as a normalizing element. Fukue et al. (2006) calculated the speciic surface area of sediment
particles assuming them to be spheres and that the speciic surface areas will be related to
the background values of heavy metals. This is consistent with the thesis that the amount of
metals sorbed onto particles is to a large extent dependent on the particle size. The results
reported by Fukue et al. (2006) using these normalization characteristics were found to be
reasonable. Santschi et al. (2001) reported that concentrations and luxes of most trace metals
found in sediment cores recovered from Mississippi River delta, Galveston Bay, and Tampa
Bay in the United States, when normalized to Al, were typical for uncontaminated Gulf
Coast sediments. Similar results can be cited with other normalizing elements. The concept
for the normalization technique is shown in Figure 8.8. The drawback of these methods is