Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 272

evidence to show that a signiicant portion of the dredged material ports, harbors, and
coastal regions is highly polluted. This realization has now energized many countries to
begin considering dredged sediments as contaminated-polluted and to insist that proper
disposal of dredged materials be obtained.
8.4 Quality of Marine Sediments
Changes in seawater quality occur quickly over a very short period because of the effect
of currents and dilutions. Although these effects may lead to low concentrations of con-
taminants in seawater, the record shows that contaminants can be (and will be) adsorbed
onto suspended and sedimenting particles. This is especially true when the settling par-
ticles are of biological origin—since they have the capability for sorbing heavy metals.
This sorption process is known as biosorption, and the sorbent is called a biosorbent.
Generally speaking, a biosorbent refers to the capability of a biomass to sorb heavy metals
from solutions. Of particular importance is the fact that biosorbents have a combination
of functional groups such as those described in Section 2.6.2 and Figure 2.13 in Chapter 2
for organic chemicals. The combination of functional groups endows the combined group
with signiicantly enhanced biosorbent capability to sorb various kinds of heavy metals—
as opposed to monofunctional groups. Microalgae, for example, are well known biosor-
bents (Wilde and Benemann, 1993). The study reported by Inthorn et al. (2002) on 52 strains
of microalgae and their capabilities for removal of Pb, Cd, and Hg from various solutions
showed that both green algae and blue-green algae functioned well in removing the heavy
metals. Although deposition of the contaminant-associated settling particles onto the sea-
bed may serve to remove a proportion of the waterborne contaminants from seawater
itself, the accumulation of contaminated particles in the sediment presents a signiicant
problem for the benthic population.
Determination of the quality of marine sediments is required for at least two different
purposes:
1. Preservation of the ecosystem. Knowledge of the types and nature of the con-
taminants in the sediments is essential, to enable one to structure the necessary
measures for remediation and management of the quality of the sediments in con-
formance with established guidelines for sediment quality.
2. Safety assurance for the lower trophic levels in the marine-derived human food
chain. Since phytoplankton and zooplankton are the irst and second trophic lev-
els, respectively, in this marine-derived human food chain, preservation of the
quality of these trophic levels means eliminating or reducing the concentrations
of contaminants in the sediments—inasmuch as these can be bioaccumulated or
bioconcentrated by the organisms that occupy these trophic levels. The record
shows that organisms such as benthos, ish, and mammals have been more or
less contaminated through the food chain and through bioconcentration (Kavun
et al., 2002; Do Amaral et al., 2005; Moraga et al., 2002). Although guidelines have
yet to be established, it is evident that in the absence of detailed records and tests,
speciication of allowable concentrations will likely be severely conservative, in
the interest of eliminating health threats to the human population.