Oil pollution wider reading Flashcards
What is pollution?
Clark et al., 2001
marine pollution = “the introduction by man, directly or indirectly, of substances or energy to the marine environment resulting in deleterious effects such as: hazards to human health; hindrance of marine activities, including fishing; impairment of the quality for the use of seawater, and reduction of amenities”
- oil spillages are included in the category of organic material waste that can be broken down by an oxidative process (by bacteria) to stable inorganic compounds such as CO2, water & ammonia (NH3)
* if the rate of input exceeds the rate of bacterial degradation = accumulation of organic materials *
If the input of wastes = large there will be intense bacterial activity until the oxidative process (degradation) exceed the supply of oxygen = deoxygenation -> degradation will be down to anaerobic bacteria (slower & potential of toxic end products, e.g. hydrogen sulphide & methane)
Can be positive if the input of organic waste is within the capacity of receiving water = enrichment BUT if capacity is exceeded = impoverishment of organisms
Al-Majed et al., 2012
oil spills cause huge economic & environmental destruction
Worst oil spill on marine water = BP rig blowout, Gulf of Mexico – 2010
Impact on organisms
Clark et al., 2001
Sublethal effects = at low concentrations
EG – physiological stress, tumours, developmental abnormalities (all may result in early death)
Larus argentatus (herring gull) – ingestion of crude oil causes damage to intestine and liver and can impair function of nasal salt glands
DOUBLE SKINS / TANKER DESIGN
Committee on Tank Vessel Design, 1991
not one cause of accident-related spills ... all causes must be considered in tank vessel design
HOWEVER can never be 100% free of spill risk
1 eg of structural prevention = double hulls = reduce pollution if grounding / collision occurs particularly effective in low-energy (low-velocity) groundings / collisions
- this design must include sufficient thickness of outer plates, cargo & ballast arrangements to ensure stability
Operational discharge
OPERATIONAL DISCHARGE – ACTIONS AGAINST
Clark et al., 2001
As well as dramatic incidents, also smaller contributions due to routine operations (not a total loss) e.g. discharge of oily ballast water & bilge water & cargo tank washings
Ballast is usually stored in cargo compartments that were previously used for oil & bc there will be some oil on the walls (= ‘clingage’) the water mixes with it, & carries the oil when disposed of
load-on-top system (in ppt) -> reduces but doesn’t eliminate input/discharge
More often crude oil clingage is removed by crude oil washing, but to avoid explosion of the petroleum the empty compartments have to be flooded with inert gas from the engine exhaust
Segregated ballast = water can be discharge without causing pollution -> progressively introduced
SOURCES
river inputs of petroleum & oils from roads by rain (always to sewage) but occasionally, storm-water overflows carry them into rivers & sea
Shipping – carry toxic substances for trade and they can be released through shipwrecks, etc
-> large scale [crude oil carriers = 350,000 tonnes] = extremely damaging
Although tanker incidents receive the most publicity, locally they’re unimportant source
Natural inputs from oil seeps occur in multiple places worldwide
Offshore oil production – dumping oil-based muds which are heavily contaminated (this accounts for 90% of the petroleum hydrocarbons entering the North Sea as a result of offshore extraction)
Atmospheric inputs – incomplete combustion of petrol or diesel from vehicles, loss of petroleum hydrocarbons to the atmosphere by evaporation from cargoes of tankers (3 750 000 t year-1)
Resources at risk
RESOURCES AT RISK
Clark et al., 2001
Rocky shores – limpets may be killed, resulting in algal dominance
Beaches – incorporated into sediment
Pelagic sea birds = large losses, but breeding populations are generally unaffected
Commercial damage:
- fisheries
- Fixed installations = particularly vulnerable
- Adult fish of commercial importance in open sea appear to avoid floating oil & ... are rarely killed
- Fish eggs & larvae = more sensitive -> in surface waters where petroleum hydrocarbons are at a higher concentration
- EG – exposure of cod eggs to water-soluble extracts of Iranian crude oil for 100 hours caused immediate casualties
- EG Amoco Cadiz wreck (1977) on the coast of Brittany
- Most harmful to shellfisheries -> the damage is persistent for years
- tainting = most important commercial damage
- Most potent source = light oils
- All crude oils, refined products, etc can give fish an unpleasant flavour even at low levels of contamination
- Concentrations of oil necessary to cause tainting varies with oil and fish: fatty fish, e.g. salmon, taint more readily
- oil is retained on shells of shellfish for a considerable time, ... is very persistent & uptake of fine droplets during filter feeding which is then incorporated into tissues
- tourism
- Causal discharge is annoying but isn’t a big issue financially because it adds little to the cost of beach cleaning that takes place anyway
- Severe pollution, however, may be treated as a national emergency (e.g. Torrey Canyon, Betelgeuse and Amoco Cadiz)
- BUT there is little evidence that tourists avoid affected beaches
Anderson, 1979 the most sensitive organisms = small crustaceans or crustacean larvae (and adult during moulting) but there’s likely to be species differences
Slick track prediction
SLICK TRACK PREDICTION
Clark et al., 2001
Oil slick = “when liquid oil is spilled on the sea it spreads over the surface of the water to form a thin film” – rate of spreading & thickness depends on sea temperature & nature of oil (light = spreads faster & thinner)
- doesn’t remain in one place -> “travels downwind at 3-4% of the wind speed”
[water currents have a greater influence in enclosed waters]
Oil at sea
OIL AT SEA
Clark et al., 2001
changes in its composition following spill
- Light fraction w low molecular weight evaporate
- Water soluble components dissolve into the water column
- Immiscible components = emulsified & disperse in wc (as small droplets)
- > occasionally a water-in-oil emulsion is produced = ‘chocolate mousse’ = viscous mass & tar balls – small SA:V ... degrade slowly
- if the oil moves into the water column its movement is controlled by currents
RESPONSES TO POLLUTION EVENTS / REDUCING ENVIRONMENTAL DAMAGE
Clark et al., 2001
banning the use of some damaging pollutants is an option but is impractical – especially w oil
-> intention is the find the least damaging disposal method (‘Best Practical Environmental Option’) whilst considering the environmental capacity of receiving waters & use the Best Available Technique Not Entailing Excessive Costs (BATNEEC) or the Best Practicable Technology (BPT)
… but the latter 2 = weaker protection
ALSO clean up options have to take into account the socio-economic value and ecological importance of an area and respond accordingly
EG – remove substratum (beach clean-up)
- dispersant spraying at sea
- hand cutting of oiled vegetation
-
Chemical dispersants
- bioremediation
- Containing /deflecting spills
- Booms: ‘sail’ above the water line and a ‘skirt’ below
- Ineffective when current speed = or + 0.7-1 knots as oil is carried over or under the boom
- Correct angle = can deflect oil from critical sites e.g. seabird colonies
- Some cases it can be collected and pumped out
- Slick-lickers
= “continuous belt of absorbent material dips through the oil slick and is passed through rollers to extract the oil”
- Only effective w small quantities of oil e.g. in harbours
-
Bean cleaning
- Fresh oil causes biological damage
- Weathered oil = smothering
- Often increases damage & delays recovery BUT often still take place due to public pressure to take action
[Contingency planning - makes response most effective & used to devel
Chemical dispersants
Clark et al., 2001
banning the use of some damaging pollutants is an option but is impractical – especially w oil
-> intention is the find the least damaging disposal method (‘Best Practical Environmental Option’) whilst considering the environmental capacity of receiving waters & use the Best Available Technique Not Entailing Excessive Costs (BATNEEC) or the Best Practicable Technology (BPT)
… but the latter 2 = weaker protection
ALSO clean up options have to take into account the socio-economic value and ecological importance of an area and respond accordingly
EG – remove substratum (beach clean-up)
- dispersant spraying at sea
- hand cutting of oiled vegetation
-
Chemical dispersants
- bioremediation
- Containing /deflecting spills
- Booms: ‘sail’ above the water line and a ‘skirt’ below
- Ineffective when current speed = or + 0.7-1 knots as oil is carried over or under the boom
- Correct angle = can deflect oil from critical sites e.g. seabird colonies
- Some cases it can be collected and pumped out
- Slick-lickers
= “continuous belt of absorbent material dips through the oil slick and is passed through rollers to extract the oil”
- Only effective w small quantities of oil e.g. in harbours
-
Bean cleaning
- Fresh oil causes biological damage
- Weathered oil = smothering
- Often increases damage & delays recovery BUT often still take place due to public pressure to take action
[Contingency planning - makes response most effective & used to devel
RECOVERY / RESTORATION
recovery times vary massively depending on the nature of the environment affected
& once recovered it won’t be identical to its previous state
Natural recovery (e.g. on coral reefs, mangroves, salt marshes) = extremely slow
Success requires a lot of understanding of the ecology of the system in question BUT there’s often a lack of knowledge
- recovery processes = costly ... habitat restoration isn’t always possible
More sheltered the shore, the longer the oil remains
Shore clean-up
Clark et al., 2001
rocks / harbour walls are cleaned by high pressure water/steam, or by dispersants
- rocky shores / boulder fields = low pressure water over a series of days moves oil to water line where it’s recovered or dispersed into the sea [high energy ... stranded oil is removed quickly]
- pebble or sand beaches = remove surface layers of substratum = damaging
... use straw/cut vegetation = absorbents
unless the oil can be dispersed into the sea, these methods produce a large volume of oil-contaminated debris that cannot be incinerated (unless oil content is high), unsuitable for dumping or oil refineries
Legislation
LEGISLATION
Committee on Tank Vessel Design, 1991
one tanker design could account for accident eventualities so the Oil Pollution Act (1990) meant that double hulls were mandatory for tankers travelling in U.S. waters – one of few legislative movements to reduce oil spills
