Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 276

discharges. Exposure to concentrations of these elements and toxicants that are higher
than the probable effects level (PEL) or effects: range—median (ERM) raises questions
relating to safety and risks to human health. Since the PEL and ERM types of crite-
ria and guidelines have been provided for determination of the direct toxic effects on
aquatic life, the potential risk to human health resulting from bioconcentration (of toxi-
cants) have yet to be fully evaluated. Excessive bioconcentration in marine species con-
stituting seafood for humans will pose problems to human health, and may well result
in chronic or acute poisoning. The Minamata disease was an unhappy happening that
originated from methyl mercury contamination of ish. This is discussed in greater
detail in a later section.
Target concentrations relecting maximum allowable background values for sediments
are necessary to provide the necessary protection for both aquatic species and human
health. These have yet to be set because (a) data on present backgrounds are not available,
(b) the links between these and bioconcentration in aquatic species and human health are
also not available, and (c) the highly variable nature of background concentrations of a sub-
stance. The variability and changing nature of background concentrations are functions of
many factors, such as sediment characteristics, local geology, mineralogical aspects of soils
near the deposited place, and discharges from land-based industries. Isolating discharges
from land-based industries allows one to consider the deviation of the background con-
centrations with sediment type as an indication of a range of tolerable intake.
8.4.3 Sulfide and Its Effects on Marine Life
8.4.3.1 Toxic Sulide
An excess of sedimentary organic matter might lead to high bacterial sulfate reduction
rates, oxygen depletion, and the subsequent release of toxic hydrogen sulide, especially
during the warm season (Magni et al., 2008). The effects of eutrophication on marine ben-
thic communities have been well documented (Pearson and Rosenberg, 1978). A signif-
icant reduction in survival time is obtained when individual macrobenthic species are
subjected to hypoxia and sulidic conditions (Rosenberg et al., 2001; Gamenick et al., 1996).
In general, sulide combined with hypoxia is more toxic to benthic animals than hypoxia
alone (Diaz and Rosenberg, 1995). Effects on infaunal benthos are also more acute than
on epifauna because of their frequent burrowing activities and, hence, exposure to severe
hypoxia and sulidic conditions (Hagerman, 1998).
In the Seto Inland Sea, in Japan, the qualities of seawater and sediment were degrading
up to 1970. Since the Act on Special Measures Concerning Conservation of the Environment
of the Seto Inland Sea was issued in 1973, the quality of seawater has been considerably
improved. However, to date, organic matter and nutrients have accumulated in the sedi-
ments, resulting in the production of organic matter in the sediments, and toxic hydrogen
sulide. In Japan, this situation is similar for other sea areas including ports and harbors.
For example, the sulide concentrations for the Harima-nada sediments are plotted
against ignition loss (Figure 8.2). The original data were obtained by the Ministry of Land,
Infrastructure, Transport, and Tourism (MLITT). In Figure 8.2, solid circles and squares
show sandy sediments, and the triangles indicate silt-clay sediments. The igures show
no signiicant relationship between sulide content and ignition loss because of the varied
nature of the organic content and sediment age.
The details are explained as follows: New organic sediments are possible under aero-
bic conditions because they initially contact dissolved oxygen. An excess of sedimentary