What is an incinerator?
By definition: An incinerator is an apparatus for burning waste material, especially industrial waste, at high temperatures until it is reduced to ash.
How safe is an incinerator?
There are two schools of thoughts: one saying that incinerators are part of the circular economy and they are 100% safe.
The other one, ours, says that there are toxic emissions from incinerators, namely heavy metals and dioxins.
What are heavy metals?
Heavy metals are naturally occurring elements that have a high atomic weight and a density at least 5 times greater than that of water. Their multiple industrial, domestic, agricultural, medical and technological applications have led to their wide distribution in the environment; raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the U.S. Environmental Protection Agency, and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.
What are dioxins?
According to WHO,
- Dioxins are a group of chemically-related compounds that are persistent environmental pollutants (POPs).
- Dioxins are found throughout the world in the environment and they accumulate in the food chain, mainly in the fatty tissue of animals.
- More than 90% of human exposure is through food, mainly meat and dairy products, fish and shellfish. Many national authorities have programmes in place to monitor the food supply.
- Dioxins are highly toxic and can cause reproductive and developmental problems, damage the immune system, interfere with hormones and also cause cancer.
- Due to the omnipresence of dioxins, all people have background exposure, which is not expected to affect human health. However, due to the highly toxic potential, efforts need to be undertaken to reduce current background exposure.
- Prevention or reduction of human exposure is best done via source-directed measures, i.e. strict control of industrial processes to reduce formation of dioxins.
Emissions of incinerators
Heavy metals in PM2.5.
This review analyzes the temporal and spatial trends in the distributions of As, Cd, Cr, Cu, Ni, Pb, Zn, and Hg in MSW incineration fly ash between 2003 and 2017, and estimates the inventories of heavy metals associated with the fly ash and the average levels of heavy metals in Chinese MSW based on their mass flow during MSW incineration. It was estimated that MSW incinerators in China released approximately 1.12 × 102, 2.96 × 103, 1.82 × 102, 3.64 × 104, 1.00 × 102, 7.32 × 103, 2.42 × 102, and 1.47 × 101 tonnes of Cd, Pb, Cr, Zn, Ni, Cu, As, and Hg, respectively, with the fly ash in 2016.
Distribution and leaching characteristics of heavy metals in a hazardous waste incinerator
Most of Cu, Cr, As, and Zn remain in bottom slag, and most Pb remain in fly ash.
Hg, Cd, As, Pb, and Zn transfer into fly ash mainly by evaporation and condensation.
Se and Cr transfer into fly ash mainly by entrainment.
High chlorine content favors the evaporation of Cu, Pb, and Zn.
The leachability of heavy metals in the bag filter ash is the highest.
Dioxins and the food chain
To clarify the dominant formation mechanism of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and reduce PCDD/F emissions in full-scale hazardous waste incinerators (HWIs), three tests were designed by adding different PCDD/F precursors in phenol-containing raw material. Flue gas from three stages of the incineration facility, as well as bottom ash and fly ash were collected to investigate formation pathways, emission characteristics and mass balance of PCDD/Fs. The results showed that in tests A and C, the PCDD/F emission levels were 0.02 and 0.83 ng I-TEQ Nm−3, with adding naphthalene and p-dichlorobenzene, respectively. Test B, the control group, only incinerated raw materials, resulting in 0.72 ng I-TEQ Nm−3 PCDD/F emissions. PCDD/F formation mechanism analysis suggested that high-temperature radical-molecule reaction was the dominate pathway in test A, while for test B, memory effect in the air pollution control devices (APCDs) led to high PCDD/F emissions. With the addition of p-dichlorobenzene in test C, PCDD/F levels at the quenching tower outlet were one order of magnitude higher than those observed at the inlet, indicating that the quenching tower failed to suppress the formation of PCDD/Fs. The PCDD/PCDF ratios indicate that with the abundance of PCDD/F precursors, surface-mediated precursor reaction is the dominant formation mechanism in low-temperature stages. These finding raise the following strategies for industry to control PCDD/F emissions: (1) strict regulation of the organochlorine content in feed material; (2) frequent and thorough cleaning the APCDs; (3) optimizing the injection rate of activated carbon.
Conclusions
To conclude, there is a number of toxic emissions from incinerators.
Heavy metals are water soluble and they can cross-contaminate the water and the sea and hence milk and marine organisms.
Dioxins are fat soluble and they can cross-contaminate all fat containing foods, namely milk and dairy products.
Having Irish Cement Factory burning toxic/hazardous waste creates a number of food chain problems.
More information can be found here.
Senior Lecturer and Head, Biological Sciences, UL.