Low frequency noise – An inventory of the literature and of the situation in the Netherlands Kim White 12 , Anja Versteeg 2 , Arnaud Kok 2 , Ric van Poll 2 and Annelike Dusseldorp 2 2 National Institute for Public Health and the Environment (RIVM), Centre for Sustainability, Environment and Health, Postbus 1, 3720 BA Bilthoven, The Netherlands

ABSTRACT Low Frequency Noise (LFN) is an environmental stressor causing annoyance and, potentially, sleep disturbance. It is a topic of increasing social concern. In the Netherlands, an increasing number of complaints about LFN in the home environment is filed each year. The RIVM was asked to prepare an overview on the health effects of LFN, including literature and an update on the Dutch way of handling complaints about LFN or a hum. To this end, a questionnaire was filled out by officials of municipalities, by other public authorities, and by audiologists. This paper contains an overview of LFN literature, findings of the questionnaire study and recommendations for future research on LFN.

1. INTRODUCTION

Low frequency noise (LFN) is sound consisting of very low tones. In the Netherlands, the most frequently used definition states LFN as sound between 20 Hz and 100/125 Hz. Sound beneath 20 Hz is called infrasound, ultrasound or low status sound [1,2] and is inaudible to most people [1]. Internationally, there are several definitions for LFN (up to 250 Hz or even higher), which hinders comparisons between studies. In the Netherlands, whenever it is unclear whether a sound is or is not LFN, for instance in case no sound measurements have taken place, or when the low sound is higher than 125 Hz, the sound is often referred to as a hum. LFN and hums are frequently described as a humming, droning, rumbling or buzzing sound. When people report or complain about LFN or a hum, three scenarios are to be considered [3]:

1. The LFN/hum is measurable and the sound source can be located. In this case, elimination or reduction of the sound source will be attempted. 2. The LFN/hum is measurable, but a sound source cannot be found. This can be a tough message to hear. The complainant will have to try to live with the sound. Help to learn how to do this, can be offered. 3. There is no measurable LFN or hum in the vicinity. The person reporting the hum should be advised to search for other explanations and/or try to learn to live with the situation. In this scenario, a medical condition, such as tinnitus, may cause the person to perceive a hum. This can be a very challenging and frustrating situation for someone, in which sometimes (cognitive behavioural) therapy can give some relieve.

1 kim.white@rivm.nl

The fact that these three scenarios exist, indicates the potential involvement of a team of professionals for each case. Professionals such as sound technicians, but potentially also audiologists and/or psychologists depending on the situation. A focus group on LFN/hums with members from ministries of the national government have asked the RIVM to review the international literature on LFN and to make an inventory of how complaints of LFN/hums are handled in the Netherlands. This paper contains a brief overview of some of the findings.

1.1. LFN sources Many sources of sound in general also produce LFN to some extent. Berglund et al. [1] gave an overview back in 1996, stating that LFN is common as background noise in urban areas. Because LFN is not easily attenuated by its environment (including buildings and hearing protection), it can travel great distances, up to a few kilometres [1, 4]. Because higher frequency components will have faded away with distance, it may be difficult to localize an LFN source: the recognisability of the sound source will decrease with increased distance to its source and the search area may be fairly large. We have decided to divide the LFN sources into two categories: small sources that can be found in or close to dwellings and large sources. Large sources of LFN are for instance: road, rail, air and maritime transport, industry, wind turbines, mining activities and natural sources, such as wind, waves on the shore, thunder storms and earthquakes. [1, 4, 5, 6]. Smaller sources contain mostly electrical devices, such as washing machines, refrigerators, heat pumps, cooling systems, mechanical ventilation and transformers [4].

1.2. Health effects sound in general and LFN In general, noise is seen as one of the largest environmental risk factors for public health [7, 8]. Several health effects have been found to be associated to sound in general (taking the whole spectrum into account). Noise annoyance is the most important health effect, which may in turn lead to other health effects via a stress path [8, 9, 10]. Other health effects include sleep disturbance [8, 11, 12], cardiovascular effects [8, 13, 14, 15], potential metabolic effects [16, 17], and cognitive effects in children [18, 19, 20, 21]. Considerably less is known about the health effects of LFN. A systematic review on the topic was performed by Baliatsas et al. [22]. The authors concluded that exposure to LFN is associated with severe annoyance and potentially with sleep disturbance. The percentage of highly annoyed people in the selected articles varied from 2% to 34% of the participants, indicating that the variance was quite large across studies. Similar findings were reported by van Kamp et al. [23]. Other health effects have not been proven at this point [22, 23]. The large differences in findings may partly be explained by differences in LFN definitions. Another issue in comparability of studies is that different LFN sources may well result in different patterns of annoyance and other health effects. Furthermore, other factors may have influenced the results. These factors may include acoustic differences across the different LFN sources, such as differences in amplitude modulation (AM) [24] or tonal components, and co-determinants, such as noise sensitivity [25, 26]. Other co-determinants that are known to influence the effects of noise in general have not yet been studied properly in relation to LFN [27]. 2. ASSESMENT OF THE SITUATION IN THE NETHERLANDS

The assessment of the current situation concerning LFN in the Netherlands was carried out using three starting points:

1. The number of complaints was assessed, 2. Randomly selected citizens of the Netherlands have filled out a questionnaire, 3. Professionals in the LFN field have filled out a questionnaire on complaint handling.

2.1. Number of complaints In the Netherlands, complaints about and reports of LFN or a hum can be filed at many different places, such as the municipality, the company that may own the LFN source, the Municipal Health Services (GGD), the Regional Environmental Services (Omgevingsdiensten), General Practitioners (GPs), the Dutch Foundation for LFN (St. LFg) and the Dutch Foundation for Noise Annoyance (NSG). Some of these organisations file complaints and reports in a system, for instance the Municipal Health Services (GGD) as can be seen in Figure 1. Other institutions did not have a filing system, in which case we asked them estimate the number of complaints and potential trends in time. Though we do not have absolute numbers, all organisations estimated a rising trend in the past five years [27]. This is not surprising as an increasing amount of LFN-emitting electrical devices can be found in the living environment. It is expected that this number will continue to grow due to, for instance, climate change and the energy transition. In the future, more dwellings will likely be equipped with mechanical ventilation, cooling systems and/or heat pumps [4]. It should be noted that complaints are often self-reported and not confirmed with sound measuring devices. It was thereby not possible to assess to what extent the complaints were caused by LFN indeed.

Noise in general

LFN

Figure 1. Number of noise complaints about self-reported noise in general and self-reported LFN from 2009-2020 at the Dutch Municipal Health Services (GGD) [28, 29].

2.2. Cross-sectional Research The Perception Living Environment Research (OBW) is a yearly cross-sectional survey on environmental stressors and their effects on annoyance, sleep disturbance, worry and satisfaction with the living environment. Participants, aged 16 years or older, are randomly selected from the Dutch population. Every year, one of the environmental topics receives extra attention, while the others are assessed less thoroughly. The environmental stressors include sound, vibration and odour by various sources [30]. In 2019, 3.2% of the participants (N = 2259) reported to be highly annoyed by LFN, compared to 2.2% in 2016. Of the participants, 2.6% reported to be highly sleep disturbed by LFN in 2019 [30], compared to 1.9% in 2016 [30, 31]. These results are all self-reported effects of LFN, no sound measurements have been conducted in this study. In an attempt to combine available research on LFN, van Kamp et al. [32] concluded that the prevalence of highly annoyed people is likely between 2% and 10% of the population. It was not possible to derive a more precise number, because often little is known about the actual exposure to LFN, so harmonisation of exposure and effect measures is often not possible.

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2.3. Complaint handling by organisations The RIVM has sent questionnaires on complaint handling to municipalities, regional environmental services and audiologists [27]. GPs were also approached to participate, but the national organisation of GPs informed us that they receive too many requests to be able to participate. The questionnaires contained items on the (estimated) number of complaints, actions following a complaint and collaborations with other institutions. The results indicated that large differences exist between regions in the way the handling of LFN complaints is organised. In some regions, the involved organisations have agreed on some form of protocol. For instance, in one region a complainant will first be seen by a professional to assess the exposure to LFN or a hum. When LFN/hum is found, other professionals will then try to resolve the situation or reduce the sound. In case no LFN is found, the complainant will be referred (with consent) to an audiologist to rule out a medical explanation. In case no LFN source can be found or in case a medical condition is causing the perception of LFN, the complainant will then (again with consent) be referred to a therapist, to learn how to live with the LFN. In other regions of the country, however, no measurements may be performed and a complainant may only receive advice on how to try to find an LFN source in or around the dwelling. Some municipalities refer all complaints to the Regional Environmental Services, others collaborate with the Municipal Health Services or do not use their network. The Municipal Health Services use a national protocol in case of an LFN complaint, but collaborations with other organisations vary between regions [26].

4. CONCLUSIONS

A large number of sound sources produce LFN to some extent [1, 4]. Health effects by LFN are severe annoyance and potentially sleep disturbance. Other health effects for noise in general have not been proven at this point [22, 23]. Different methods have been used to study and describe the situation concerning LFN and associated health effects in the Netherlands. There seems to be a rising trend in the number of complaints that is reported by institutions handling LFN complaints. A growing number of electrical devices in the vicinity of dwellings could be an explanation. The fact that LFN has been covered by the media in the past years could be also be (an additional) explanation. It is possible that more people mention LFN in a complaint, when previously they may have just reported noise annoyance. It is important to note that in many cases of complaints, the actual exposure to LFN is unknown. Results from cross-sectional research indicate that the number of highly annoyed and highly sleep disturbed people by LFN may be rising as well. However, the exposure of the participants was unknown. It struck the researchers of this study that complaint handling varies largely across regions. It is advised that the organisations that are involved in LFN complaints in specific regions try to organise a more fluent way to handle complaints by collaborating with peers. This could ensure that people feel that their complaint is taken seriously. The LFN research field is hindered by the fact that multiple definitions are used, many LFN sources are to be considered and different methods are used to assess both LFN itself and the perception thereof. It is therefore often very difficult to draw any conclusions, when we do not know if people are actually exposed to LFN and if so, at what levels, and to what extent studies and situations are comparable. More research on LFN is needed, concerning, for instance, exposure and effect studies, studies on best practices concerning complaint handling and studies on specific LFN sources and their effects. 5. ACKNOWLEDGEMENTS

We gratefully acknowledge the contributions made by dr. Irene van Kamp. Furthermore, we would like to thank the organisations that have filled out questionnaires and the Municipal Health Services (GGD) for sharing their complaint registrations.

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