Unit 2 - Environmental Impacts
The sections below describe the impacts (environmental/ecological, public health and socioeconomic impacts) of HNS spills at sea.
Considering our society's dependence on chemicals and consequently the constant growth in the volume of chemicals that are transported by sea, it is essential to understand their potential hazardous impacts in case of a spill.
Incidents of HNS can encompass a wide range of temporal and spatial impacts, varying from short-term localised events to incidents covering vast areas and lasting for many months. The adverse impacts of chemical incidents can include human health effects, environmental and ecological damage, and commercial and amenity disruption.
2. Environmental / Ecological impacts
Shipping incidents of HNS can cause immediate and potential long-term adverse effects on marine habitats and ecosystems (e.g. destruction of marine habitats; sub-lethal and lethal effects on marine organisms; visible detriment to beaches, coastlines and wildlife).
Note: The MSC Napoli which towed to Lyme Bay, Devon (UK) (in 2007), and carried >1600 t of chemical products (e.g. nonylphenol) classified by IMO as dangerous goods, RAISED AWARENESS OF THE POTENTIAL ECOLOGICAL RISK OF HNS SPILLS.
Ecosystems may take many years to recover from an incident, particularly when the chemicals involved are persistent, of low solubility and low volatility.
The effects of an HNS released into the marine environment will depend on a number of FACTORS such as:
- Behaviour of the substance.
- Toxicity of the material (dependent on how large a dose is required to kill an organism; the more toxic a substance the smaller the dose required).
- Quantities involved.
- Resulting concentrations in the water column and/or sea floor.
- Sea conditions in the affected zone such as turbulence, surface and deep currents, presence of thermoclines and haloclines (i.e. local oceanography). They affect the chemical distribution through the water column and/or its loss at the water surface.
- Length of time organisms are exposed to that concentration (i.e. exposure time).
- Level of tolerance of the organisms (which varies greatly among different species and during their life cycles).
Note: Persistence of the HNS in the marine environment can also play a factor, particularly in the case of sinkers and floaters, by greatly increasing a potential risk area when dilution has little or no effect in reducing the concentration.
Incidents involving releases to marine waters have the benefit of sea and air dilution, to decrease the concentration of a substance to below a lethal dose. However, lower doses can produce SUBLETHAL EFFECTS to marine organisms over a wider area. These effects can produce some form of damage which may be detrimental to marine environment (i.e. individual organisms, species, populations or marine communities) over a longer term, depending upon the persistence of the released HNS in the marine environment. For example, chemically-induced stress can reduce the overall ability of an organism to grow, reproduce, feed (i.e. to survive) or otherwise function normally within a few generations. More specifically, sublethal effects include:
- Damage to internal organs;
- Damage to fins;
- Pre-cancerous growths;
- Skeletal deformities;
- Reduction in reproductive success.
These effects may not be readily detectible in individuals but could cause changes in the community structure of a marine area impacted by an HNS incident.
Some forms of HNS material (where not directly toxic) can damage the marine ecosystems by causing CHANGES IN THE ENVIRONMENT. Such changes include:
- Variation in salinity and pH, together with deoxygenation when material is broken down or used biologically in the marine environment (e.g. fertilisers, palm oil, etc.).
Changes in environmental conditions can induce LETHAL EFFECTS in marine ecosystems. However, it should be noted that:
- Such effects can be limited to the wreck site and immediate dilution area.
- The significance of such effects is dependent on the location of the incident (e.g. changes in salinity and oxygen content in an estuarine or already polluted area may have little impact due to the natural tolerance of the resident marine community, while there may be a greater effect on pristine reef communities).
Biologically inert material which does not have a toxic or environmental effect may have an impact due to SMOTHERING OR BY CHANGING THE PHYSICAL NATURE OF AN AREA (e.g. a sinker settling over a bottom, resulting in a change to the habitat of the benthic ecosystem). This is also likely to be limited to the immediate area of the incident site, although currents can redistribute HNS material.
In addition to HNS behaviour, processes such as BIOACCUMULATION and BIOMAGNIFICATION determine the compartments of the food web affected. The characteristics of some HNS (particularly heavy metals and some organic compounds) can result in bioaccumulation. Sessile marine species that filter seawater for food, such as bivalve molluscs, are particularly vulnerable to this phenomenon. Subsequent biomagnification may also occur if the chemicals can be passed on, following the food chain up to higher predators (e.g. top predators of marine communities - fish, birds, marine mammals and humans). Therefore, the higher trophic level organisms can be exposed to enriched concentrations of contaminants in their tissues via their prey.
Note: Bioaccumulation is defined as the process by which organisms accumulate chemicals both directly from the abiotic environment (i.e. air, water, soil) (direct exposure) and from dietary sources (trophic transfer), resulting in detrimental impacts over a much wider area, even to a global scale. Thus, this process consists in the sorption of contaminants in the organisms faster than its elimination. More information on the bioaccumulation process and the factors that influence bioaccumulation can be found in Hodgson (2010) (pages 535 – 539).
Current knowledge of HNS effects ...
An understanding of the ecological hazards involved in HNS spills is less well recognized than that involving oil spills. There is a current paucity of knowledge about the effects of HNS on marine biota and the relatively few data available on the HNS ecotoxicology are mostly from experiments conducted with freshwater organisms. For example, reproduction impairment due aniline toxicity has been reported for freshwater Crustacea Daphnia magna (Abe et al., 2001; Kühn et al., 1989) and acute toxicity shown for sand shrimp Crangon septemspinosa (McLeese et al., 1979).
Therefore, the toxicity and ecological impacts of HNS on marine organisms are poorly understood, making it difficult to predict the effects on marine ecosystems and to prepare contingency plans for these substances.
In order to respond to incidents involving HNS, the systematic classification of scientific ecotoxicological data for marine organisms should be a priority issue.
The following recent studies were performed to improve the knowledge on the effects of HNS to marine organisms:
Prioritisation of HNS
The HNS that pose major environmental risks to European waters can be found in the following article:
3. Public health impacts
Environmental impacts are often more obvious than human health effects. However, human health effects caused by HNS incidents can include:
- Toxicological effects (acute and chronic) - such effects may happen when humans are exposed to chemicals after a chemical spill. The main routes of exposure are through:
* Inhalation (gaseous or volatile chemicals; e.g. products of combustion or an airborne plume); * Ingestion (contamination of water supplies or food (e.g. fish)); * Dermal contact (release of solids or liquids).
Note: Acute - Exposure characterized by a time period of short duration; commonly used to describe single-dose exposure in toxicity studies; Chronic - Exposure characterized by a time period of long duration; commonly used to describe long-term (6-12 months) exposure in toxicity studies.
According to the revised GESAMP hazard evaluation procedure, the principal mode of human exposure after spillage is expected to be through vapours. Thus, the human exposure is likely to occur predominantly from air-borne contamination and consequently inhalation exposure.
Both acute and chronic health effects are recognized following acute releases of chemicals. These effects may affect all major body systems (e.g. cardiovascular, respiratory, immunological and neurological systems). Reproductive effects may occur whilst some chemicals may be teratogenic (i.e. cause birth defects). Some chemicals may also be associated with cancer (i.e. carcinogens). Moreover, some chemicals may have a secondary impact upon those coming into contact with casualties (e.g. health workers) and may also have delayed effects such as respiratory oedema.
Some examples of pathologies due to chronic intoxication can be seen in the next picture:
- Mental health effects - Such effects are determined by exposure to the chemicals spilled and the event itself, even if exposure is unlikely. Major chemical incidents have the potential to disrupt the lives of victims through impacting upon health, loss of relatives or other lives, property and employment as well as through environmental degradation. Victims of incidents can experience long-lasting mental health problems.
- Physical effects - for example, explosions following heating of tanks containing chemicals can result in traumatic injuries from shock waves, projectiles and fragments. Additionally, fires can produce physical injury through the production of heat.
Prioritisation of HNS
A methodology has been established for prioritisation of HNS, based upon potential public health risks. HNS were assessed using conventional methodology based upon acute toxicity, behaviour and reactivity. Analysis of 350 individual HNS identified the highest priority HNS as being those that present an inhalation risk. For more information consult the following article:
4. Environmental and public health impacts of the main HNS behaviour groups
Substances released into the marine environment could pass into the air (gas clouds), onto the water surface (floaters), into the water column (dissolvers), to the sea floor (sinkers), or a combination of these. These substances may contaminate indirectly, all the organisms in these compartments and other users of these compartments in the event of an accident at sea. Specific information on the HNS behaviour (main groups) in the environment, their environmental and public health impacts as well as the organisms / species most affected can be found in the following document:
Therefore, substances with different behaviours at sea provide different impacts to marine organisms. However, DISSOLVERS AND SINKERS are the substances that might cause the HIGHEST POTENTIAL ECOLOGICAL IMPACTS ON THE MARINE ENVIRONMENT after a spill as they will disperse easily, and hence may be bioavailable for aquatic organisms, both in the water column and the sediments.
From the HUMAN HEALTH PERSPECTIVE, the chemicals of priority concern are those that have some CAPACITY FOR EVAPORATION (i.e. gases and evaporators; e.g. toluene, benzene) and which may induce a health effect. These substances would tend to be governed by atmospheric parameters.
Hazards to marine environment and humans
Human populations as well as the marine environment can be exposed to spilled hazardous chemical substances, as already mentioned. Nine potential hazards can be distinguished when chemical substances enter the marine environment. The hazards are listed in Table 1 and described accordingly for each behaviour category.
Table 1 - Most relevant hazards of chemical substances within a behaviour category for humans and the marine environment.
Therefore, each behaviour has its own relevant hazard aspects. For example, toxicity to human populations and explosivity are typical hazard aspects of substances which pass into the air after a release as can be observed in table 1.
5. Socioeconomic impacts
Some examples of socioeconomic impacts due to an HNS spill are:
- Commercial value of marine resources reduced. This can be observed, for example, in:
* Marketed fish with fin erosion, skeletal and/or growth deformities; * Seafood that present a change in the organoleptic characteristics (a phenomenon known as Tainting).
Example: Styrene (a Floater/Evaporator; reactive product (exothermic polymerization), irritant and flammable) causes tainting of edible organisms, i.e. causes a change in the organoleptic characteristics of the flesh of fish and shellfish (observed in the CHUNG MU N°1 SPILL INCIDENT, China, 1995).
- Closure of fishing and aquaculture areas due to a contamination of commercial fish and shellfish by a toxic substance that have the capacity to bioaccumulate. The loss of fishing and aquaculture resources implies economic losses from business interruption.
- Amenity value of an area reduced for economic drivers such as tourism because of the contamination of this area (e.g. through the pollution of amenity beaches and bathing/recreation waters).
There is also the impact of “public perception”, whereby the impact of an incident can be magnified if public opinion considers that the area is not safe to visit or consumer products (e.g. fish, shellfish, etc.) from the location are polluted.
Some examples of property damage / economic losses can be seen in the following figure:
6. Important Documents
The International Maritime Organization created a group of experts on Scientific Aspects of Marine Environmental Protection (GESAMP)link title. Extensive work has been undertaken by this group for the international conventions to identify the hazards associated with HNS material and classify the potential safety, health and environmental risks.
GESAMP, an advisory body to the United Nations, has published evaluations of the effects of substances transported by ships on the marine environment (hazard evaluation procedure - 1st edition: 2002)link title. This easily accessible and simple guide can provide an important first step in evaluating the severity of a chemical spill. The properties of the chemicals have been evaluated in relation to a number of predefined effects:
A = Bioaccumulation and biodegradation; B = Aquatic toxicity (acute and chronic aquatic toxicity); C = Acute mammalian toxicity; D = Irritation, corrosion and long term mammalian health effects; E = Interference with other uses of the sea.
The 2nd edition of the hazard evaluation procedure of GESAMP was published recently:
Data regarding effects of individual HNS cargoes can also be obtained from substance specific Safety Data Sheets (SDS) which summarise the various hazards associated with each substance. SDS commonly provides toxicological and ecological information, etc.
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