Environmental Engineering Reference
In-Depth Information
flounder, blue mussel, prawn, isopods, and crabs) to static (DC-induced) magnetic
fields of 3700 µT for several weeks and detected no differences in survival compared
to controls. In addition, they exposed shrimp, isopods, echinoderms, polychaetes, and
young flounder to a static, 2700 µT magnetic field in laboratory aquaria where the
animals could move away from or toward the source of the field. At the end of the
24-hour test period, most of the test species showed a uniform distribution relative
to the source, not significantly different from controls. Only one of the species, the
benthic isopod
Saduria entomon
, showed a tendency to leave the area of the magnetic
field. The oxygen consumption of two North Sea prawn species exposed to both static
(DC) and cycling (AC) magnetic fields were not significantly different from controls.
Based on these limited studies, Bochert and Zettler (2006) could not detect changes
in marine benthic organisms' survival, behavior, or physiological response param-
eters (e.g., oxygen consumption) resulting from magnetic flux densities that might be
encountered near an undersea electrical cable.
The current state of knowledge about the EMF emitted by submarine power
cables is too variable and inconclusive to make an informed assessment of the effects
on aquatic organisms (CMACS, 2003). Following a thorough review of the literature
related to EMFs and extensive contacts with the electrical cable and offshore wind
industries, Gill et al. (2005) concluded that there are significant gaps in our knowl-
edge regarding the sources and effects of electrical and magnetic fields in the marine
environment. They recommended developing information about likely electrical and
magnetic field strengths associated with existing sources (e.g., telecommunications
cables, power cables, electrical heating cables for oil and gas pipelines), as well as
the generating units, offshore substations and transformers, and submarine cables
that are a part of offshore renewable energy projects. They cautioned that networks
of cables in close proximity to each other (as would be substations) are likely to
have overlapping, and potentially additive, EMF fields. These combined EMF fields
would be more difficult to evaluate than those emitted from a single, electrical cable.
The small, time-varying B field emitted by a submarine three-phase AC cable may
be perceived differently by sensitive marine organisms than the persistent, static,
geomagnetic field generated by the Earth (CMACS, 2003).
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Chemicals that are accidentally or chronically released from hydrokinetic and
ocean energy installations could have toxic effects on aquatic organisms. Accidental
releases include leaks of hydraulic fluids from a damaged unit or fuel from a ves-
sel due to a collision with the unit; such events are unlikely but could potentially
have a high impact (Boehlert et al., 2008). On the other hand, chronic releases of
dissolved metals or organic compounds used to control biofouling in marine appli-
cations would result in low, predictable concentrations of contaminants over time.
Even at low concentrations that are not directly lethal, some contaminants can cause
sublethal effects on the sensory systems, growth, and behavior of animals; they may
also be bioaccumulated (i.e., filter feeders such as limpets, oysters, and other shell-
fish concentrate heavy metals or other stable compounds present in dilute concentra-
tions in seawater or freshwater).
