Characteristics of Hazardous Wastes
The simple definition of hazardous waste that “Any waste that has the potential to harm human health or the environment is hazardous waste” is not adequate from a legal standard point.
Therefore, the Resource Conservation and Recovery Act (RCRA) legislation in the US defined hazardous waste as a waste, or combination of waste, which because of its quantity, concentration, or physical, chemical or infectious characteristics may:
– Cause or significantly contribute to an increase in mortality or increase in serious irreversible illness; and
– Pose a substantial present or potential hazard to human health or environment when improperly treated, stored, transported or disposed of.
According to EPA, waste is hazardous if it meets one or more of the following criteria.
- It exhibits the characteristic of hazardous waste
- It is a non-specific source waste.
- It is a specific commercial chemical product or intermediate.
- It is a mixture containing a listed hazardous waste.
- It is a substance that is not excluded hazardous waste RCRA.
Characteristic of Hazardous Waste
Available procedures are accurate enough to enable definition of the four characteristic of hazardous waste i.e. ignitability, corrosivity, reactivity and toxicity.
However, test protocol and data interpretation for measuring carcinogenicity, mutagenicity, phytotoxicity and potential bioaccumulation are either poorly developed or too complex and require high level of expertise.
1. Ignitability
Ignitability is the characteristic used to define hazardous waste as those waste that could cause a fire during transport, storage or disposal. Examples of ignitable waste include waste oils and used solvent. It has the following properties;
1. It is a liquid, other than aqueous solution containing less than 24% alcohol by volume and has flash point less than 60˚C (140˚F).
2. It is not a liquid and is capable, under standard temperature and pressure, of causing fire through friction, absorption of moisture, or spontaneous chemical changes, and when ignited, burns so vigorously and persistently that it creates a hazard.
2. Corrosivity
This is a characteristic of hazardous waste that is measured by pH. Waste containing materials of very high or very low pH can produce dangerous reaction with other materials in the waste or cause toxic contaminants to migrate from certain waste. Examples are acidic wastes from many industrial processes. The corrosive materials have the following properties.
1. It is aqueous and has the pH of <2 or > 12.5 as determine by pH meter
2. It is a liquid and corrodes steel at rate >6.35mm per year at a test temperature of 55oC (130oF).
3. Reactivity
Some constituents of a waste may be unstable and may have the potential to cause explosion at any state of the waste management cycle. Used cyanide solvents and water from TNT operation are example of reactive waste.
1. It is normally unstable and readily undergoes violent changes without detonating.
2. It reacts violently with water.
3. It forms potentially explosive mixture with water.
4. When mixed with water, it generates toxic gases, vapors or fumes sufficiently enough to endanger human health or environment.
5. It is cyanide or sulfide bearing waste which when exposed to pH condition between <2 and >12.5, can generate toxic gases, fumes and vapors that can endanger human health and environment.
4. Toxicity
Read Also : Characteristics of Municipal Solid Waste (MSW)
Is the ability of a substance to cause death, injury, or impairment to an organism that comes in contact with it. Modes of contact are ingestion, inhalation and dermal contact.
A waste will be considered as toxic if, using the standard test method, the extract from the representative sample of the waste contains the following at greater or equals to respective value.
| Chemical | Maximum allowable concentration (mg/L) |
| As | 5 |
| Ba | 100 |
| Cd | 1 |
| Cr | 5 |
| Pb | 5 |
| Hg | 0.2 |
| Se | 1 |
| Ag | 5 |
Concept of toxicity
Adverse effect such as carcinogenicity, mutagenicity and teratogenicity are generally linked to contact with toxic materials and may also be used as a criteria in a listening of hazardous wastes.
Read Also : Sources of Industrial Wastes
However, the term ‘toxic’ and ‘hazardous’ are not interchangeable. Toxic denotes the capacity of a substance to produce injury while hazardous denotes the probability that injury will result from the use of (or contact with) a substance.
Acute toxicity refers to the toxic effects that have rapid onset, a short course and pronounced symptoms. Acute toxic waste may injure human and mammals when inhaled or ingested or upon contact with skin.
Acute toxicity is typically measured in terms of lethal dose concentration (LD50) in which 50% of the test population will die from the exposure to a particular substance under prescribed condition.
Chronic toxicity refers to the effect that persists over a long period of time. Chronic toxicity measurements are not nearly as standardized as acute measurements due to inability to maintain human being or mammal under long term controlled condition.
