Database
The National Pollutant Inventory (NPI) gives information on the types and amounts of pollutants being emitted to the Australian environment. This document has background information about how the NPI substances were chosen, and explains some of the concepts and definitions relating to substance emissions.
A panel of technical experts was formed in March 1997 to recommend substances for inclusion on the NPI. The Technical Advisory Panel (TAP) used a risk-based approach for recommending which substances should be on the reporting list.
The TAP first developed criteria for selecting substances to the reporting list. These criteria were:
The TAP considered 420 substances against these criteria. The list included some agricultural and veterinary substances but excluded substances that were:
All substances on the 'master list' were scored against each of the above criteria. The hazard scores varied between 0 and 3 for both environmental effect and human health. For example, the health hazard score for lead and compounds was 1.75, and the environment hazard score for lead and compounds was 2.5.
These hazard scores were used to generate a number which approximated the relative risk that each substance poses in Australia. This risk is expressed as:
Risk Score = (Environment Hazard Score + Human Health Hazard Score) x Exposure
The risk scores generated by this process fall between 0 and 18. They were used to rank the substances. The TAP recommended that substances with a risk score of 3 or higher should be included on the NPI. There were 90 substances which scored 3 or higher in this process and all of these substances are on the reporting list. This approach means that substances with a high hazard score but low likelihood of exposure to Australia's population or environment may have a lower risk rating (hence lower NPI rank) than substances with a lower hazard score but higher chance of exposure.
There are fact sheets on the NPI web site for the 90 substances on the NPI reporting list . The fact sheets have information about how you might be exposed to the substance, how exposure might effect you and the environment, common uses, comparative data and physical and chemical properties.
The thresholds for reporting are based on amounts of substance handled or processed, rather than quantity of substance emitted, as a trigger for reporting. This means that where a facility (such as a factory or a site) handles more than the threshold amount of a substance, the operator of that facility must prepare a report to the NPI each year detailing the amount of that substance emitted by the facility.
This is a practical approach to measuring emissions. A user of substances will be more able to determine how much is used in a process than how much is emitted. If the threshold is triggered based on usage, then the more difficult determination of how much is released to the environment can be made.
Diffuse emissions are from sources like motor vehicles and stormwater runoff, as well as from facilities that do not reach reporting threshold levels. Estimation of these emissions are undertaken by state and territory environment agencies
Diffuse emissions are not estimated annually.
By the end of 2004, 33 airshed studies and and 32 catchment studies were completed for the main urban and rural areas in Australia.
The most significant contributor to diffuse source emissions across Australia are motor vehicles.
Standards or guidelines for protecting the environment, public health or workers' health are designed to limit exposure to hazardous and polluting substances to an acceptable level. The determination of what is an 'acceptable' level is complex. In part, this depends on what the receiving environment ( either air, water or land) is to be used for..
Using river water as an example, the acceptable concentration of lead in the water will depend on what the water is to be used for.
If the water is to be used for human drinking water , the Australian drinking water guideline value for maximum concentration of lead is (0.01 mg/L) and is calculated to protect the health of people drinking that water.
If the water is to be used for irrigating crops, the guideline value is set to protect the health of people or animals who eat the crop being irrigated. In this case, however, a higher concentration (0.2 mg/L) is considered acceptable because lead binds very effectively with most soils and does not move readily within plants. This means that little of any lead in the irrigation water will find its way into the crop. However, care would need to be exercised if irrigation were practiced over a long period with lead-containing waters to ensure that no excessive accumulation of lead in soil occurred.
If the water is to be protected for environmental purposes - i.e. no direct human use of the water - the guideline value (0.001 to 0.005 mg/L, depending on the hardness of the water) is set to protect the health of the plants, fish and other animals inhabiting or using the water. This value is lower than the value for protecting human health because it takes into account that the organisms it is intended to protect are typically completely immersed in the water for the whole of their lives (e.g. fish) and that lead bioaccumulates in fish and other aquatic organisms. These organisms may also have a different sensitivity to lead than humans.
As another example, benzene is used in industrial processes as well as emitted from cars. This substance may be present in the air in the factory that uses the substance as well as in the 'open air'. A higher concentration in the factory air than in the 'open air' may be considered acceptable. This is because the concentration considered acceptable in the factory takes into account the fact that individual workers are not in the factory 24 hours per day, every day, and therefore they are not exposed to the higher concentrations all the time. Setting the standard or guideline value to protect worker health would also take into account the extent to which the substance accumulates in the worker's body over time. Another factor sometimes relevant to worker health is that people in the workforce are generally more able to resist the effects of pollution than the more vulnerable sections of the community, such as the very young, the infirm and the elderly.
The main difference between 'standards' and 'guidelines' in environmental regulation is that 'standards' are legally enforceable and 'guidelines' are advisory documents only.
Australia's Constitution sets out the powers of the Australian government, with the states and territories having primary responsibility for the environment. To promote a uniform national approach the Australian government coordinates the preparation of 'guidelines' for environment protection through the National Resource Management Ministerial Council (NRMCC).
State or territory governments may use the values in 'guidelines' when making laws to establish 'standards' to protect the environment.
'Hazard' is the harm potentially caused by a substance. For example, chromium (VI) compounds have a high hazard rating with respect to human health, because they have the potential to cause a range of lethal and serious sub-lethal effects on humans.
'Risk' is a measure of the likelihood that actual harm will be caused by a substance. If one is not exposed to any chromium (VI) compounds the risk of suffering harm caused by those substances is zero. The amount of risk increases with the amount of exposure. The relationship between risk and hazard is usually expressed as:
Risk = Hazard x Exposure
'Exposure' is a measure of the quantity of a substance the at-risk organism has to deal with. Exposure is usually measured in terms of concentration (e.g. milligrams per litre) of substance in the environment and length of time the organism is subjected to that concentration of substance.
The NPI stores data on total quantities emitted per year, not concentration of substances in air, water or soil. For example, while chromium emissions to a city's total atmosphere could be added up, this would be a poor indicator of likely exposure, since 'hot spots' are likely to be concentrated around specific sources and not spread generally through the city's air.
Exposure is very important in assessing the impact an emission will have on health or environmental risk. For example, the emission of a certain quantity of benzene from a factory vent may result in a significantly higher exposure for people living in within half a kilometre of the factory, than the same quantity of benzene from traffic spread over a ten square kilometre area. Similarly the exposure of those people living within the vicinity of the factory will be quite different depending on whether the emission of benzene is from a stack at factory roof level or from a stack of 100 metres in height.
To better understand exposure, it is necessary to analyse the NPI emissions data further. Typically, the data are first processed through an atmospheric dispersion model, which incorporates variables such as stack heights, emission flow rates, pollutant characteristics, terrain, vegetation, and local or regional meteorological conditions. Alternatively, ground level monitoring data may be used. The output from the atmospheric dispersion model provides an estimate of ground level concentrations of substances which, for some substances, may be compared with various guideline values or standards, where these exist. Good examples of such comparison standards are the values provided by the National Environmental Protection Measure for Ambient Air Quality for the six listed pollutants. State and territory environment agencies may have data available on the concentration of some substances..
NPI emissions data alone is not enough to make an assessment of the risks to human health and the environment from exposure to a substance. The specific characteristics of the substance and circumstances in which exposure occurs must also be considered.
'Absorbed dose' is the quantity of a substance actually absorbed by an exposed organism. This is the quantity which determines the type and extent of effect (the 'response') caused by the substance to the organism. It is important to distinguish between 'exposure' and 'absorbed dose'. As described above, 'exposure' is a measure of the concentration of a substance in the environment, and the length of time an organism is subjected to that concentration. The concentration of the substance and the duration of exposure help determine the absorbed dose. The way the response changes as the absorbed dose changes is often called the 'dose-response function'.
Not all of the substance in the environment will be absorbed by exposed organisms. For example, the air we breathe in contains about 20% oxygen but because we don't absorb all of the oxygen we are exposed to, the air we breathe out still contains enough oxygen to support mouth-to-mouth resuscitation of someone who has stopped breathing. In general, the amount of a substance absorbed depends on:
The bioavailability of a substance refers to the ability of organisms to absorb the substance. It often varies considerably depending on the chemical form of the substance. For example, the bioavailability of chromium metal is very low - it is insoluble in water and chemically relatively inert. Similarly, many of the naturally occurring forms of trivalent chromium (CrIII) - which occurs in many soils - are generally insoluble and biologically unavailable. However, most compounds containing the hexavalent form (CrVI) are readily soluble in water making this species of chromium more biologically available.
Bioconcentration refers to the higher concentration of a substance in an organisms tissues than in the environment. For example, oysters, mussels and many other bottom dwelling 'filter feeders' are very efficient at extracting heavy metals from the water in which they live but because they do not excrete these substances the concentrations build up in the organism’s tissues. Microorganisms in the water may also change the chemical form of the substance to make it more biologically available. For example, inorganic mercury compounds dissolved in polluted estuarine water may be converted to organic mercury compounds which are stored by an oyster in its tissues. Organic compounds of mercury are more readily absorbed by other organisms (such as humans) that eat the oyster.
Bioaccumulation refers to the accumulatation of a substance in the tissues of plants and animals to a concentration higher than that of the surrounding environment. For example, oysters or other marine life in areas contaminated by mercury may absorb that mercury but may not excrete it, so the concentration of mercury in the oyster increases with time. Similarly, the concentration of mercury in humans who eat mercury-contaminated oysters will increase over time if they continue to eat contaminated oysters. This may continue until symptoms of mercury poisoning arise.
Speciation refers to the subdivision of classes of substances into groups with closely related properties (e.g. compounds of chromium can be subdivided into groups defined by the oxidation state of chromium (e.g. III or VI) within the compound). This is a useful way of categorising substances, because substances with similar properties behave in the environment in a similar way and often have similar types of effects on human and environmental health. Likewise, substances with different properties (i.e. different species) are likely to behave in different ways and have different effects on human and environmental health.
To understand how these terms are used in relation to the estimation of emissions, it is necessary to understand the ideas of systematic errors in estimation and random errors in estimation.
Consider how we might estimate the total amount of benzene emitted by all the motor vehicles in Australia in a year. In general terms, the total amount of benzene emitted by Australian cars in a year will be given by the total quantity of fuel used by cars in a year multiplied by the amount of benzene per kilogram of this fuel.
A systematic error in this estimate will occur if we have used an incorrect value for the amount of benzene per kilogram of fuel. The result will be an inaccurate estimate.
Random error in the estimate occurs in situations where we use an 'average' value for one of the parameters. This would occur if:
Each regional value will probably be slightly different from the others and the average of all regions, that is, the regional values are distributed about the average: some are greater and some are less than the average. In general, we will not know the 'true' value so we use the average as an estimate of that 'true' value. The uncertainty caused by the spread of observed values about the average is called random error, and the size of the spread of observed values about the average is a measure of the precision of the estimate.
Another way of understanding the difference between these terms is to think of throwing darts at a dart-board. If, when aiming for the bullseye, you consistently hit the twenty for example, this is 'precise', but not 'accurate'. (Of course, if you were aiming for the twenty, this result would be both 'precise' and 'accurate'.) If your darts are spread evenly but widely around the bullseye, this is 'accurate' but not 'precise'. The following diagrams illustrate this difference.
What has this got to do with the NPI? In many cases, the quantities of emissions in the NPI database are not directly measured, but are estimated using an 'emission estimation technique' (EET). In the case of emissions from diffuse sources , the quantities in the database are always the result of estimations. A great deal of effort has gone into developing these estimation techniques so that they are as accurate and precise as possible. In some cases the information on which they are based is not as precise as in other cases, so the precision of estimates may vary between substances and between industries. For example, estimates of the amounts of nitrates and nitrites in the emissions of a facility are likely to be more precise than estimates of the amounts of these substances resulting from nutrients in urban run off.
Movement of polluting and hazardous substances from their sources into the environment depends on both the medium which carries them, such as exhaust plumes and drainage streams, and the conditions in the environment which receives them. As pollutants enter the environment they can:
Some of the environmental factors which control the movement of pollutants into the environment are:
Substances emitted into the environment by human activity or natural processes may interact with each other within organisms such as humans, animals or plants, or in the environment. These interactions may change the effects on the environment or human health. There are four main types of interactions: