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Journal of Applied Sciences and Environmental Management
World Bank assisted National Agricultural Research Project (NARP) - University of Port Harcourt
ISSN: 1119-8362
Vol. 8, Num. 2, 2004, pp. 71-75
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Journal of Applied Sciences & Environmental
Management, Vol. 8, No. 2, Dec, 2004, pp. 71-75
Short Communication
Aquatic Oil
Pollution Impact Indicators
1ENUJIUGHA,
V N; 2 *NWANNA, L C
1. Dept.
of
Crop Production
2.Dept.
of
Fisheries and Wildlife
Federal University of
Technology, P. M. B. 704, Akure, Nigeria.
*Corresponding author
Code Number: ja04029
ABSTRACT
Aquatic
oil pollution impact indicators such as oil-grease, low dissolved oxygen
concentration, increased biochemical oxygen demand, increased water temperature
and acidity
of the water are associated with aquatic habitat degradation, reduced productivity
and or loss of biodiversity. These impact indicators are interrelated and
connected in a chain reaction that a severe shift in any of the parameters
will induce
negative changes in others. For instance, introduction of significant quantities
of crude oil into the aquatic ecosystem will cause increase in biochemical
oxygen demand, reduction in dissolved oxygen concentration, increased temperature
and pH of the water body. The resultant effect of these abnormal shifts in
the impact indicators is disorders in the physiological status and reduction
in the immune status of aquatic organisms, which may lead to mortality. Therefore
to ensure sustainable management and optimum exploitation of the aquatic
resources, it is necessary to set safe limits for the pollution impact indicators.
This
paper reviews the deleterious impacts of these indicators on the aquatic
habitat and productivity, and establishes the safe limits for each impact indicator
in relation to the freshwater, brackish water and marine
ecosystems. @JASEM
The study of the environment
and the impacts of human activities on natural ecosystems has recently assumed
a worldwide focus. Obviously, mans constant quest to fully utilize the product
of the environment has led to the production of wastes in such proportions
as to threaten the very existence of certain strategic ecological habitats
and directly or indirectly affects human
population. According to Sheehan et al. (1984), releases into the environment
of persistent chemicals lead to an exposure level which ultimately depends on
the time the chemical remains in circulation, and how many times it is circulated
in some sense, before ultimate removal.
Spills are uncontrolled
releases of any product including crude oil, chemicals or waste caused by
equipment failure, operation mishaps, human error or intentional damage to
facilities.
The extent of damage depends on what, where and how much has been spilled
and how long it remains in the immediate and impacted environment (SPDC, 1997).
High inertia and elasticity are properties expected of a physically and chemically
varying ecosystem with an extensive history of pollutant stress. In the case
of crude oil releases, especially where the recipient environment is aquatic,
the impacts are in the range of unquantifiable damages to fishes and other
economically important aquatic organisms, as well as the direct and indirect
negative effects on the socio-economic lives of human settlers whose survival
has much to do with the
products of aquatic environment.
The problems of point oil spills
remain a serious concern. By point oil spills reference is made to occasions
when a significant amount of a chemical (in this case, hydrocarbons) has entered
in ecosystem at a point (in both space and time) and effects of contamination
are expected in a well-defined more or less
local area (Sheehan et al., 1984). The assumption is that the oil does
not rapidly diffuse away, but remains in the immediate vicinity at a noticeably
high concentration, or perhaps moves, but in such a way that levels remain
high as it moves.
Apart from uncontrolled
oil spills, production operations inevitably release effluent in the form of
produced waters, storm waters and flushing wastes into the aquatic environment
and these are found to contain significant quantities of hydrocarbons and associated
pollutants. For instance, a major crude oil terminal in the Niger Delta was
found to empty its effluent directly into the brackish waters of Warri River
with hydrocarbon content of the effluent being well over the permissible limit
for such environment (SEEMS, 1997).
The question
that immediately probes ones mind is: How do we predict both the volume of
oil pollution and the obvious environmental impacts by some measurable parameters,
and how do we set limits for these parameters with respect to the different
aquatic environments? Then also one is faced with the question of how the environmental
performance of oil industry operators can be assessed and adequately improved
upon. This paper seeks to address these questions, especially as it concerns
the oil industry in Nigeria. Commendably the Federal Environmental Protection
Agency (FEPA) and the Department of Petroleum Resources (DPR) have recently
come up with guidelines
for evaluation of environmental performance.
The Choice of Major Pollution
Impact Indicators: The first thing that comes to mind in the selection
of major aquatic oil pollution impact indicators is an understanding of those
environmental attributes which influence the survival of aquatic life, such
that a shift in the ecosystem balance and biodiversity usually results from
an alteration in their measurable proportions. Obviously, the boundaries
of natural ecosystem are determined by the environment, that is, by what
forms of life can be sustained by prevailing environmental conditions. In
this light the choice of parameters has to do with maximum productivity of
fish and other aquatic life as well as the well-being of human dwellers and
their farmlands in cases where flooding are witnessed or recorded.
According to
Damaskos and Papadopoulos (1983), the generally accepted indicators of water
quality are dissolved oxygen (DO) and the biochemical oxygen demand (BOD).
High oxygen depletion can be so severe as to affect fish life. If the DO
value falls below the minimum oxygen requirement for the particular species
of fish,
they are subjected to stress, which can result in mortality. The oxygen content
of natural waters varies with temperature, salinity, turbulence, the photosynthetic
activity of algae and plants, and atmospheric pressure. Chapman and Kimstach
(1992) noted that DO concentrations below 5mg/1 adversely affect the functioning
and survival of biological communities, and below 2 mg/1 may lead to the
death of most fish. The optimum concentration of DO for fish and other aquatic
life
is given in Table 1.
Table
1: Optimum environmental conditions
for fish and aquatic life.
Environmental
Parameter Optimum value/range
Dissolved
oxygen (DO) 5 7 mg/1
Biochemical
oxygen demand (BOD) 10 20 mg/1
PH 6.0 9.0
Temperature 9 34° C
Total
dissolved solids (TDS) 1,600mg/l
Copper 0.1mg/1
Sources: Chapman
and Kimstach (1992); Chatopadhyay et
al. (1988)
The BOD is estimated
by the amount of oxygen required for the aerobic microorganisms (in the case
of oil pollution, hydrocarbon degraders) present in the water body to oxidize
the organic matter to a stable inorganic form. Thus, when we say that a water
body has a BOD value of đ mg/1 we mean that the concentration of biodegradable
organic matter in one litre
of it is such that the micro-organisms need đ mg of oxygen in order to be
able to oxidize it. The result of a study carried out by Chattopadhyay et
al.
(1988) indicated 10 20 mg/1 as the optimum BOD range for fish culture in effluent
or polluted waters. The addition of significant quantities of crude oil to any
water body causes an immediate rise in the BOD due to the activities of hydrocarbon
degraders and the blockade of oxygen dissolution.
Changes in pH
(or the hydrogen ion activity) can indicate the presence of certain pollutants,
particularly when continuously measured and recorded, together with the conductivity
of a water body. The pH of 1 unit could result in an increase of lead by
a factor of 2.1 in the blood of an exposed organism (Sheehan et
al., 1984). What is known, of course, is that pH changes can drastically
affect the structure and function of the ecosystem, both directly and indirectly
by, for example, increasing the concentration of heavy metals in the water
through increased leaching from sediments. Helz et al. (1975) found
out that cadmium, which is toxic to many organisms, could be readily
remobilized from sediments.
It is important
to note that the pH of any water body is dependent on its temperature. And
temperature affects physical, chemical and biological processes in water
bodies and, therefore, the concentration of many variables. According to Chapman
and
Kimstach (1992), increased temperature increases the rate of chemical reactions
and decreases the solubility of gases (especially oxygen) in water. Respiration
rates of aquatic organisms increase leading to increased oxygen consumption
and increased decomposition of organic matter.
Crude oil is
associated with some toxic heavy metals most of which contaminate the oil
through underground deposits, especially lead and chromium. Iron is in great
abundance
in tropical and subtropical aquifers and is also associated with crude oil
deposits. High iron concentrations in groundwater are widely reported from
developing countries, where iron is often an important water quality issue.
Some metals also get into oil due to pipeline ageing and corrosion. Metal-induced
depression of productivity most certainly occurs and may persist in polluted
aquatic systems. Certain organisms have been shown to have some ability to
regulate levels of copper and zinc in muscle (Sheehan et
al., 1984). However, bioaccumulation of metals such as lead and chromium
by fish is expected, and this spells danger to the human populations consuming
such fish. Results obtained by Rai and Chandra (1992) show marked accumulation
of copper, manganese, lead, and iron by the alga Hydrodictyon reticulatum under
both field and laboratory conditions. Fish usually preys upon algae and other
planktonic and benthic organisms; and when there is bioaccumulation of heavy
metals in fish, there is likelihood of morbidity and mortality in man along
the food chain. Usually bioaccumulation of toxic metals can occur to certain
extent
before chronic-effects thresholds are reached.
An important
indicator of significance in aquatic oil pollution monitoring and control
is the actual volume of oil released, which is approximated
by the milligrams of oil in a litre of the water. Oil pollution, apart from
causing depletion of oxygen and suffocation of aquatic species, affects plants
and cultivated
crops in lowland areas characterized by seasonal flooding. Ilangovan and Vivekanandan
(1992) working with blackgram (Vigna mungo) concluded that oil pollution
in soil might deplete oxygen at the rhizosphere because of possible depletion
of soil oxygen by hydrocarbon-degrading micro-organisms and, therefore, oil
polluted soil directly affects the overall physiology of the plant as evidenced
by lower
levels of macro and micro-biomolecules of the plant as well as polarity, thereby
reducing plant growth. According to these workers, as a result of continuous
aqueous oil effluent irrigation in about 25 acres of crop field, oil compounds
infiltrated up to 50cm depth of the soil. Also total phenolic content of the
leaves in the plant increased significantly.
Limits of Major Indicators
for the Freshwater Environment:
The activities of major oil field
operators, especially in Nigeria, are such that unavoidable hydrocarbon releases
into the immediate environment are expected. This is particularly the case
in flowstations, gas plants and compressor stations where effluent are generated
during normal production operations. Facilities located in inland areas, especially
environments characterized by seasonal flooding, contribute immensely to environmental
degradation thereby endangering both aquatic life and human settlers within
the vicinity. Oil spillage obviously decreases aquatic productivity and impacts
negatively on the economic and social lives of local fishermen. DPR (1991)
has outlined a set of standards/limits of some major oil pollution impact indicators
in oilfield effluent released into freshwater environments. The limits for
physico-chemical parameters and mineral concentrations are presented in Tables
2 and 3.
Table
2: The DPR Limits of major physico-chemical parameters in effluent inputs
into freshwater and marine environment.
Parameter Freshwater Marine
PH 6.5 8.5
Temperature
(O C) 35 35
Salinity
(mg/1) 600 2,000
Oil and
Grease (mg/1) 10 20
Turbidity
(NTU) 10 15
BOD (mg/1) 2,000
TSS (mg/1) 30 50
Source: DPR
(1991)
Table
3: DPR Limits for Heavy metal
concentrations in fresh water environments.
Parameter Concentration
(mg/1)
Lead 0.05
Iron 1.5
Copper 1.0
Zinc 1.0
Chromium 0.03
Source: DPR
(1991)
And relative
to the volume of oil pollution in the immediate and nearby environments, these
parameters usually reveal impact magnitude by the degree
of deviations
in their measured values
from set limits.
Examining the oil-grease input
into the environment and comparing with DPR limit of 10 mg/1 can easily assess
the environmental performance of oilfield operators in the inland areas. Figure
1 shows the oil-grease content of a flowstation effluent in the Niger Delta
determined over a one-year period (December 1995 November 1996). The presentation
which is adapted from SEEMS (1997) show that produced waters as point sources
have their compositions affected by factors other than separator efficiency.
For instance, the percentage of lift-gas applied for oil-water separation may
largely depend on the subjective assessment by
production personnel.
It is expected
that substantial dilution of the effluent will occur to such as extent that
the recipient freshwaters when examined will conform to World Health Organization
(WHO) standard. For example the WHO turbidity limit for freshwaters is 5
NTU (Chapman and Kimstach, 1992). Heavy metal content is also greatly reduced
by
algal growth. Of course, algae are know to concentrate many trace metals
in their tissues, and as the algae die and sink, their metal content may
be carried
down to the sediments. However, the danger is in the consumption of the algae
by fish which accumulate them to levels toxic to man.
Limits Of Impact Indicators
In Estuarine And Marine Environments
The brackish water and marine
environments are generally characterized by high salinities, total solids and
temperatures compared to freshwaters. Whenever there is a spill or oil influx
into such environments, the main concern must be the volume of oil spilled
as well as turbidity and suspended solids content. Heavy metal composition
is of lesser interest, as sea waters are known to contain trace metals in significant
concentrations (Helz et al., 1975).
DPR (1991) gave
limits of some important physico-chemical parameters for anthropogenic inputs
into estuarine and marine environments in Table 2. The maximum allowable oil-grease
concentration is 20 mg/1 for effluent released into offshore environment. This
is only for produced waters, especially for facilities in swamp locations.
These are of course controlled releases, and do not include well flushing and
equipment repair/maintenance waste waters.
Seawater salinities
above 2,000 mg/1 show clearly the presence of pollutants which may impact estuarine
fish species. Biodiversity sustainability is of utmost importance as a shift
in ecosystem balance may result in stress and depression of certain susceptible
species. It is important to note that for every salinity value of 35,000 mg/1,
the sodium content is 10,770 mg/1 with sodium/salinity ratio put at 1:3.26
(SEEMS, 1997). This means that high salinity might not be favourable for aquatic
life.
CONCLUSION
We have examined
the important indices for evaluating the severity or otherwise of aquatic
oil pollution impact. The choice of these variables is found to be governed
by
the consideration of aquatic productivity and socio-economic life of human
settlers. The limits for anthropogenic or controlled effluent inputs have
been assessed both for freshwater and estuarine/marine environments. From the
foregoing,
a conclusion can be drawn that regular environmental performance evaluation
of oilfield activities must be the hallmark of any meaningful environmental
policy. Continuous effluent monitoring and environmental evaluation are needful,
as even the controlled inputs into the environment are not consistent in
their composition
of important parameters. Regulatory agencies such as the Federal Environment
Protection Agency (FEPA) and the Department of Petroleum Resources (DPR) have
a
task of seeing to the implementation of environmentfriendly progrmames by the
oilfield operators.
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Sciences & Environmental Management
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