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Survey of chemical substances in headphones and hearing protection aids

1 Summary

As a part of the Danish Environmental Protection Agency’s survey of chemical substances in consumer products, knowledge of which materials and substances can be found in headphones and hearing protection aids is established. The project was conducted in two phases, the first phase being a survey of the market with focus on information from producers and suppliers, supplemented with information from the Internet, while the second phase elaborated these results through a material analysis of selected products and use of knowledge about polymer materials as available from literature and experiences at FORCE Technology. The project results in a general assessment of the potential risks for consumers from using the products in question and an outline of a project which can establish a more precise assessment by using the approach described in the EU Technical Guidance Document for risk assessment of chemicals.

In the first phase of the project about 70 producers of headphones were identified and the number of different products was estimated to be more than 1,000 products. The product group was divided into three sub-groups, i.e. Around-ear, On-ear, and In-ear headphones. The three sub-groups differ significantly in their design, and potentially also in the choice of materials which come into contact with the skin. No special considerations were given to the fact that many headphones today are integrated with a microphone, so-called head-sets, as there is no indication of alternative materials coming in contact with the skin for these products. Based on different statistical sources it is estimated that 500,000-1,000,000 headphones are sold in Denmark each year.

In the first phase of the project 16 suppliers of hearing protection aids were identified. This product group was divided into two sub-groups, i.e. Around-ear and In-ear. The latter group does in the current project not include single-use products, for which a survey has been conducted earlier. The amount of different hearing protection aids is much lower than the amount of headphones, especially for In-ear products where each producer in general only markets one basic product. The amount of sold hearing protection aids to private consumers is crudely estimated to 10,000 per year, while the amount sold for professional use probably is significantly higher.

Searches on the Internet and contacts to producers established a good overview of which materials are commonly used in the two product groups, but only sparse information about which additives are used to give the desired material properties. It is not surprising that this information is not readily available, given the fact that the materials are selected and bought from raw materials suppliers, based on the technical specifications, while it is less important for producers of headphones to know how the properties have been incorporated in the materials. It is, however, noticed that many of the producers answering a questionnaire answer that their products are ROHS-compatible, i.e. they have no or very limited content of certain heavy metals and flame retardants.

In the second phase of the project, FT-IR analysis of 20 products was performed, comprising 14 headphones (6 Around-ear, 4 On-ear and 4 In-ear) and six hearing protection aids (4 Around-ear and 2 In-ear). The main objective of the analysis was to identify the primary materials, while they could only provide information about additives and fillers if these were present in large concentrations. Additives used in small concentrations are thus not identified, nor is the presence of heavy metals.

The following table summarizes the materials which are known from the survey and the analysis to be used in headphones and hearing protection aids.

The approach and scope of the project does not establish precise knowledge about which materials are used most frequently, this will require that more answers from producers are received and/or analysis of more products. Based on the available information it seems, however, credible to assume that PUR (polyurethane) is frequently used, both because it is found in a large part of the products examined and because it is known to possess the desired properties with respect to e.g. user comfort and wear resistance. Also silicone is frequently used, especially in In-ear products where its flexibility makes it well-suited for adaption to the geometry of the inner ear. PVC was not identified in the headphones subjected to analysis, but was identified in three out of four hearing protection aids, either with phthalate as plasticiser or modified with nitrile-rubber.

The results of the analyses made in the project were supplemented with an analysis of the chemical content in the components of a head-set (i.e. a headphone with an attached microphone), kindly provided by a manufacturer. This analysis was primarily aimed at identifying and quantifying substances with allergenic properties, but it also provided information about the amount of other substances present in the product, of which some are known to have effects on human health. With respect to the risk of allergy it is concluded by a recognized research institute that allergic reactions cannot be expected from use of the product examined. In the current project, it is furthermore concluded from the analysis that the amounts of identified substances with effects on human health in the product are so small that they most probably do not pose a risk. It is, however, emphasized that other products within the product group may contain other substances – and in larger amounts. Furthermore, it should be recognized that the analysis made for the producer does not allow for a good estimation of the exposure levels. For this purpose, an analysis of the amount of migrating substances is needed.

With the limited knowledge established in the survey and analysis of the products only a very general assessment of the potential risks to human health can be given. In analogy to other surveys of products with similar materials and exposure routes it is, however, concluded that the risk of being exposed to harmful substances in significant amounts seems to be very small. As indicated, the basis for this conclusion is very limited, and more precise conclusions can only be reached by performing a series of analyses giving the information necessary to conduct a risk assessment of the identified substances using the EU Technical Guidance Document (TGD) for risk assessment of chemicals.

As the final activity in the project a suggestion for the content of a follow-up project is outlined, giving the possibility of making the desired risk assessment following the TGD. The suggested analysis programme focuses specifically on skin exposure, since exposure via inhalation or oral ingestion is judged to be negligible or not existing.

It is also suggested that the analyses to be made comprise chemicals and groups of chemicals known from other surveys to have a potential for effects on human health which may come close to a Margin of Safety of 100, e.g. plasticizers, metals, organotin-compounds, and brominated flame retardants. The outlined approach does, however, also allow for identification and quantification of the migration of other chemicals, which may be relevant in a risk assessment. The suggested analysis programme thus gives the possibility of identifying potential risks with respect to human health, but it is emphasized that the product groups being examined are very heterogeneous with respect to materials (and additives), and the results obtained will probably not be very conclusive.

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Version 1.0 April 2008, © Danish Environmental Protection Agency