Languages:
Home » PCBs » Level 2 » Question 7

PCBs Polychlorinated biphenyls

7. What are the risks posed by PCB exposure?

  • 7.1 What health effects occur at what levels of exposure?
  • 7.2 What tolerable daily intakes have been established for PCBs?
  • 7.3 What are estimated daily intakes of PCBs?
  • 7.4 What are the uncertainties in assessing PCB health risks?

The risks posed by PCB exposure have been evaluated by analysing data from studies using PCB mixtures most commonly used in industry, to which workers may have been directly exposed.

This approach has been preferred to other scientific approaches in this case, because of the availability of appropriate data. In other cases, assessment methods may focus on "dioxin-like" health effects of different PCBs (through the use of toxic equivalent factors) or on actual measures of total PCB body burden in humans.

As PCBs persist in the environment, the general population is still potentially exposed to a variety of PCBs via food, air, and water. Although mixtures used in industry are not identical to the combinations of PCBs present in the environment (or in breast milk), these mixtures have been found to have similar harmful effects.

The studies on humans showed several types of health effects linked to PCB exposure. Findings from animal studies have been used to quantify the human health risks posed by exposure to different amounts and mixtures of PCBs. This is largely because in studies on humans that had been exposed there is insufficient information about the degree and type of PCB-exposure or about simultaneous exposure to other potentially harmful substances.

This text is a summary of: IPCS - WHO Polychlorinated biphenyls : Human health aspects. Concise international chemical assessment document 55
Section 10, Evaluation of health effects 

7.1 What health effects occur at what levels of exposure?

A series of long-term studies carried out on large numbers of rhesus monkeys showed that exposure to a mixture of highly chlorinated PCBs (Aroclor 1254) caused adverse effects on their immune system at intake levels as low as 5 000 ng/kg body weight per day (LOAEL).

Exposure to PCBs over a longer period of time was shown to negatively affect the development of the nervous system leading to behavioral and learning problems in monkeys. Comparable results have been found in human population groups with similar exposure histories. In monkeys, the lowest dose at which such behavioral changes were observed was 7 500 ng/kg body weight per day (LOAEL).

Only at much higher levels have PCBs been shown to induce tumors in the liver of rodents.

Overview: Levels of human exposure to PCBs and Tolerable Daily Intake (TDI)

This text is a summary of: IPCS - WHO Polychlorinated biphenyls : Human health aspects. Concise international chemical assessment document 55
Section 10.1, Hazard identification and dose response assessment  

7.2 What tolerable daily intakes have been established for PCBs?

Tolerable Daily Intake (TDI) is an estimate of the amount of a substance that can be taken in by humans on a daily basis over a lifetime without appreciable human health risk.

For a typical PCB mixture (Aroclor 1254), a Tolerable Daily Intake for humans of 20 ng/kg body weight per day was determined based on the lowest level of PCBs that gave rise to adverse effects (LOAEL) in a particular animal species (rhesus monkeys).

In order to determine this Tolerable Daily intake for humans the lowest level of PCBs that gave rise to adverse effects in animals (LOAEL) was divided by an overall uncertainty factor of 300, which takes into account possible differences in susceptibility between humans and experimental animals and between different individuals.

The available data are not sufficient to determine tolerable PCB concentrations in air or what doses can be ingested over a short period of time without appreciable health risk.

This text is a summary of: IPCS - WHO Polychlorinated biphenyls : Human health aspects. Concise international chemical assessment document 55
Section 10.2, Criteria for setting tolerable intakes and tolerable concentrations for PCB mixtures Section 10.2, Criteria for setting tolerable intakes and tolerable concentrations for PCB mixtures 

7.3 What are estimated daily intakes of PCBs?

In the USA, estimates of the daily intake of PCBs from the main sources of exposure have been calculated. The total daily intake from drinking water, air, and food (listed from lowest to highest) is believed to range from 1 to 8 ng/kg body weight.

Table: Estimated daily PCB intakes in the USA in adults

Source Estimated daily intakes
in ng/kg body weight per day
Comments
drinking-water Less than 0.2 Based on a 70-kg individual drinking 2 litres of water per day, which contains 6 ng/litre [0.006ng/m3]of PCBs
air 0.3 to 3 Based on the typical range of urban PCB levels of between 1 and 10 ng/m3
food 0.5 to 5 Fish, poultry, and meat are the primary contributors to the PCB intake
Total 1-8  

The estimated total daily intake is approximately 1 000 times lower than the lowest PCB intake that caused adverse effects in animals (5 000 ng/kg body weight per day) and 4 times lower than the tolerable daily intake for PCBs (20 ng/kg body weight per day).

Overview: Levels of human exposure to PCBs and Tolerable Daily Intake (TDI)

This text is a summary of: IPCS - WHO Polychlorinated biphenyls : Human health aspects. Concise international chemical assessment document 55
Section 10.3, Sample risk characterization 

7.4 What are the uncertainties in assessing PCB health risks?

This assessment of PCB health risks is limited by several uncertainties:

  • Laboratory animals (rhesus monkeys) used in the studies on which the calculation of a Tolerable Daily Intake is based may be more sensitive to PCB exposure than humans.
  • Studies were only carried out on a limited set of PCB mixtures, which may not fully represent actual exposures.
  • Most studies consider only mixtures of PCBs – rather than individual congeners – that might have different mechanisms of action.
  • The risk assessment reflects the exposure of the general population, but may not adequately cover certain circumstances, such as eating large amounts of PCB-contaminated fish or breathing air containing elevated PCB levels downwind of contaminated sites.

This text is a summary of: IPCS - WHO Polychlorinated biphenyls : Human health aspects. Concise international chemical assessment document 55
Section 10.4, Uncertainties in the health risk assessment 


FacebookTwitterEmailDownload (21 pages, 0.4 MB)
Themes covered
Publications A-Z
Leaflets

Video