5.1
This chapter carefully considers issues raised by inquiry participants: first, the fears that, in the past, individual community members may have been directly exposed to chemical insecticides; and, second, the concerns that local cases of cancer and autoimmune disease might be connected to the use of chemical insecticides.
5.2
The chapter concludes with a discussion of evidence to the inquiry regarding the feasibility and value of any further investigations.
Issues raised by inquiry participants
5.3
Discovery 3227 and most individual submitters were worried that community members had been repeatedly exposed to unsafe levels of chemical insecticides. Inquiry participants thought that the use of spraying or fogging techniques meant community members had been in direct contact with chemical insecticides. They were especially concerned about the possible use of insecticides containing organophosphates, such as temephos.
5.4
Submitters explained that they were fearful these alleged chemical exposures had caused many cases of cancer and autoimmune disease among current and former residents of Barwon Heads.
5.5
Discovery 3227 suggested that cancer and autoimmune diseases had been caused by aggregate chemical exposures over time. Discovery 3227 also suggested that the chemical insecticides used for mosquito control may have disrupted endocrine function for some individuals and that this may have triggered the development of cancers and autoimmune diseases.
5.6
The following sections consider these issues raised by submitters alongside relevant evidence from state and local government authorities and evidence from expert witnesses.
Exposures to chemical insecticides
5.7
As discussed in chapter 2, a majority of individual submitters expressed the view that the City of Greater Geelong (City) and former council entities had sprayed mosquito insecticides in ways that might have exposed community members to harmful chemicals.
5.8
Discovery 3227 expressed its belief that mosquito spraying by the local council used a ‘mosaic of chemicals’ made up of two types of pesticides: organophosphate insecticides and pyrethroid insecticides. Discovery 3227 alleged that the council’s use of barrier spraying and fogging techniques to control mosquitoes had exposed many in the community to these chemical insecticides, in a number of named locations in Barwon Heads:
… within our Village Park , houses adjacent to the wetlands, the kindergarten, the Caravan Parks, the Football oval surrounds, the Barwon Heads Primary School inclusive of sports days ,the schools out of bounds area and the boundaries of the school for the period of 1980 to the early 2000’s.
5.9
Another submitter also believed that organophosphorus-based pesticides (OPs) had been sprayed in the township of Barwon Heads:
From the 1980’s onwards Barwon Heads was sprayed and bombed with Organophosphorus insecticide (OP) to alleviate mosquitos. This practice occurred at a high rate well into the 2000’s.
5.10
Ms Ainsworth told the committee that she and others remembered residential streets being regularly fumigated and gutter drains being regularly sprayed and appearing pink when sprayed; and that she remembered ‘foul-smelling, foggy mist’ in the community park. Ms Ainsworth told the committee she believed that she and her friends had been exposed to chemicals when they rode their bikes in the mist.
5.11
Some other submitters also referred to their memories of a fog or mist after mosquito treatments in the town of Barwon Heads.
Organophosphate insecticides
5.12
The active ingredients in OPs are organophosphates, which are chemical compounds of phosphoric acid. Since the 1940s OPs have been used for a wide range of applications, including as insecticides for pest control. In recent decades, concerns over health and environmental impacts and toxicity have led to greater restrictions on the use of some OPs, especially in relation to non-target species such as fish and other aquatic life.
5.13
Discovery 3227 alleged that local councils used OPs for mosquito control on the Bellarine Peninsula for several decades, including temephos, malathion, fenthion, dicholorvos, diazinon and chlorpyrifos. Discovery 3227 claimed that the council was using organophosphorus insecticides via fogging and residual barrier spraying from the 1980s into the 2000s.
5.14
Other individual inquiry participants also expressed concerns about exposure to organophosphate insecticides. For example, Ms Kristie Ainsworth told the committee:
I strongly believe that the town's cancer and autoimmune cluster is a direct result of the organophosphates used to treat mosquitoes by the City of Greater Geelong.
Temephos (larvicide)
5.15
Discovery 3227 alleged that the City and former council entities used temephos-based products for mosquito control in and around Barwon Heads over several decades:
Temefos [sic] has been used extensively … for about 30 years by the City of Greater Geelong in some shape or form. They used it in a pellet form, which they dumped in hundreds and hundreds and hundreds of kilos into our wetlands, but they also used to spray it for mosquitoes in the village park and those areas where adult mosquitoes roost.
5.16
Evidence from the department and from the City states that Abate (temephos) was a mosquito larvicide normally used in solid formulations (powder or pellets). For example, Mr Lyndon Ray informed the committee that the larvicide Abate (temephos) was mostly applied by hand to bodies of water containing mosquito larvae.
5.17
Mr Ray further explained that Abate was not a product that was fogged, since it was not used for adult mosquito control.
5.18
The City also gave evidence that in the 1980s and 1990s mosquito larvicide use in Australia began to transition away from OPs towards more use of biological insecticides, like Bacillus thuringiensis israelensis (Bti) and s-methoprene.
5.19
At a hearing in 2020, Mr Sodomaco, who had been a council employee since the 1980s, told the committee that Abate was used between 1984 and 1987, and then again in 1998 during a helicopter trial. Stocktake information and other documentation submitted by the City supports these statements.
5.20
At the hearing at Barwon Heads in 2021, the City was asked again about its past use of Abate (temephos). Mr Gareth Smith confirmed that Abate was used for a three-year period in the 1980s, and then again on 23 October 1998, when Abate was dropped at five locations during a trial of larvicide application by helicopter.
Other organophosphate pesticides (OPs)
5.21
Discovery 3227 alleged that the City also used other OPs for mosquito control, including fenthion and malathion. Mr Harrison submitted that these allegations are founded on three things: references to malathion in the 2004 Framework for mosquito management in Victoria (framework document) as a registered adulticide; the mention of a number of OPs in archived Victorian Government website content from 1996, which states that malathion, fenthion and several other OPs were registered for use as mosquito larvicides; and a mention of a fenthion-based product (Baytex 550) in stocktake documents from 1994 provided by the City.
5.22
Malathion was not identified by the City or the department as one of the products used for mosquito control on the Bellarine Peninsula.
5.23
The committee asked the City about one mention of five litres of Baytex 550 (fenthion) in its historical timeline of mosquito product use. The City stated that, while this product appears in a stocktake list for a chemical shed, it was in fact not used for mosquito control and therefore need not have appeared in the timeline.
5.24
The City also explained that it had enquired of staff about any possible uses for Baytex 550 at that time:
Existing City mosquito management staff who have worked on the program for over 30 years, recalled this product possibly being used for bull ant control by directly applying it to the ant’s nest and did not believe it was ever used for fogging or applying to mosquito larvae.
5.25
Fenthion was not identified by the City or the department as one of the products used for mosquito control on the Bellarine Peninsula.
5.26
Discovery 3227 also identified several other chemicals that it believed the City had used for mosquito control in the 1980s and 1990s, including chlorpyrifos, diazinon and dichlorvos. Evidence submitted by the department and the City does not substantiate this.
5.27
At a hearing, Mr Steve Sodomaco confirmed to the committee that Abate (temephos) was the only organophosphate insecticide used by the City for mosquito control.
Pyrethroid insecticides (adulticides)
5.28
As mentioned above, Discovery 3227 alleged that many in the community were regularly exposed to pyrethroid insecticides used by the City for mosquito control.
5.29
Pyrethroids are synthetic versions of the active ingredients in natural pyrethrum (known as pyrethrins) and have been used in mosquito insecticides since the 1980s. Pyrethroid-based insecticides are adulticides, targeting adult mosquitoes, and are applied via ultra-low volume (ULV) fogging techniques. This kind of fogging is not visible like the thermal fogging techniques that are used for pyrethrum-based products.
5.30
A historical timeline of product use submitted by the City shows occasional use of synthetic pyrethroid insecticides between 1988 and 2005 and regular use of biological insecticides from 1988 onwards.
5.31
The department and the City provided details about the historical use of two pyrethroid-based insecticides on the Bellarine Peninsula. Twilight (phenothrin) was applied via ULV fogging in 2007, 2010 and 2012. One drum of Reslin (biomesrethrin), a product used in a similar way, is listed in a stocktake list dated 31 March 1999 but with no information available about whether or when it was applied. Any community exposures to pyrethroid-based insecticides are most likely to be on the occasions of Twilight use in 2007, 2010 and 2012.
5.32
The Victorian Chief Health Officer (CHO) advised the committee that synthetic pyrethroids are safe for use, comparing them with domestic mosquito-control formulations:
The information provided to the Inquiry by CoGG [the City of Greater Geelong] indicates that only synthetic pyrethroids or natural pyrethrins were used for fogging. To improve the effectiveness of synthetic pyrethroids and natural pyrethrins, piperonyl butoxide is often added as a synergist. These fogging agents used by CoGG can be found on supermarket shelves, including flyspray products. An example is Raid Earth Options Botanicals Multi-insect Killer, which contains 3.5g/kg of pyrethrins and 16.1g/kg of piperonyl butoxide. In comparison, the control agent, Pyfog, that was used by CoGG, contains 4g/L of pyrethrins, and 12g/L of piperonyl butoxide.
5.33
The scant use of synthetic pyrethroids on the Bellarine Peninsula is consistent with the national pattern of use reported in a 2017 article, which refers to the infrequent use in Australia of pyrethroid fogging:
Australia does not carry out routine fogging. [If required,] pyrethoids are used in highly regimented and limited fashion.
Disease causation
5.34
As discussed in chapter 2, some submitters believed that these alleged chemical exposures had caused some Barwon Heads residents and regular visitors to develop cancers. Other submitters raised concerns about a possible link between chemical insecticides and cases of autoimmune disease in the community.
5.35
Mr Ross Harrison of Discovery 3227 stated that he believes exposure to certain chemicals has occurred and is directly linked to the diseases experienced by people who have lived or regularly holidayed in Barwon Heads. Mr Harrison explained that his own investigations had led him to believe that the community had experienced:
… a mosaic disease burden covering specific significant cancers and immune disease—not the result of one pesticide but a group of OP [organophosphate] pesticides and synthetic pyrethroids.
5.36
One submitter described their hope that the inquiry might provide answers to the question of what had caused the illnesses of some in the community:
For me this is also about understanding why there are so many ailments suffered around the place that I grew up in. I would like to know if these chemicals are the cause of my own and others’ ailments (cancer, autoimmune, and other rare health issues) …
Cancer causation
Level of exposure
5.37
The Potential Cancer Cluster Expert Advisory Group (Expert Advisory Group) stated in May 2021:
We acknowledge the difficulty that members of the public often have in understanding that exposure to a carcinogen in and of itself does not lead to cancer. It requires exposure at a sufficiently high level to cause cancer.
5.38
The Expert Advisory Group restated its opinion that, for community members in the Barwon Heads area, ‘any exposures were very likely to have been at insufficient levels to cause cancer’.
5.39
Similarly, Professor Bernard Stewart, a cancer cluster specialist and professor of public health and chemical causation of cancer at the University of New South Wales, and Dr Roger Drew, an accredited consultant toxicologist, both advised that the highest risk of a chemical exposure causing cancer lies with the product manufacturers and applicators, and that members of the general community were unlikely to have been exposed sufficiently to the chemicals in question, even via fogging.
5.40
Dr Drew advised that the Australian Pesticides and Veterinary Medicines Authority (APVMA) is the authority with the best information about safe and unsafe exposures to specific chemical formulations, as its risk assessment for each product uses raw data provided by the product manufacturer. Dr Drew said:
… the regulatory authorities have at their hands much more information than does IARC [the International Agency for Research on Cancer]. IARC evaluates the hazards of chemicals. It does not ask the question: what level of exposure is required to cause the cancer?
5.41
At the November 2020 hearing, Dr Drew, a toxicologist with expertise in risk assessment, explained to the committee that, if there had been any community chemical exposures, these may not have been sufficient to cause cancer:
… in relation to chemicals causing cancer … the majority of that data with humans comes from occupational exposure, where the exposures are really very high. The situation you have here is a potential community exposure, and the question is: are those exposures sufficient to cause cancer?
5.42
Professor Watterson of the Occupational and Environmental Health Research Group, Stirling University, Scotland, commented on the value of exposure data in determining specific risk to individuals. However, Professor Lin Fritschi, John Curtin Distinguished Professor of Epidemiology, advised the committee of the difficulty of determining details of any historical pesticide exposure for community members:
… you don't know what the dose was. You don't know who was exposed at a high level and who was exposed at a low level, and finding that information is quite difficult.
5.43
Professor Watterson also stated that all individuals are exposed to a wide range of substances and that it is ‘extremely difficult’ to determine whether a person may have been exposed to specific chemicals. He said:
Usually you are going to get people exposed to a whole range of things by a whole range of routes. People may be exposed because people are using them in the environment, or they may be in their food, or they may be in the water.
5.44
An individual with expertise in pathology, toxicology and epidemiology submitted that it was scientifically unlikely that environmental exposure to chemical pesticides would lead to cancer:
Neither epidemiology nor toxicology supports the idea that exposures to environmental levels of synthetic industrial chemicals including pesticides are important as a cause of human cancer.
Chemical insecticides used on the Bellarine Peninsula
5.45
The department submitted that the chemical insecticides used historically and currently by the City are not known to cause either cancer or autoimmune disease in humans:
… none of these chemicals is known to cause cancer or autoimmune disease in humans during normal use by or for the public, or by workers when the product is used according to the label …
5.46
In May 2021, the CHO again confirmed that the department does not believe that any of the chemical insecticides used by the City (temephos and synthetic pyrethroids) are associated with cancer causation:
The mosquito control agents that the Department of Health understands were used by the City of Greater Geelong (CoGG), are not known to cause leukaemia or other cancers.
5.47
This statement is supported by evidence from other scientific experts. For example, Professor Fritschi advised the committee there is insufficient evidence of an association between cancer and the insecticides used to control mosquitoes.
5.48
Professor Driscoll, a specialist in cancer clusters, cancer epidemiology and occupational and environmental medicine, also advised the committee that no exposures had been found that might have caused cancer:
… we haven't seen suggestions of significant levels of cancer-causing exposures over this time in this area. I agree that causes should be looked at, but my understanding is that, to the extent they can be, they have been looked at.
5.49
The CHO advised the committee that ‘temephos is not known to cause cancer’. An individual submitter also advised that scientific reviews of temephos have found no evidence that it is carcinogenic.
5.50
The City advised that, although it no longer uses temephos, temephos is still registered by the APVMA for use in mosquito control.
5.51
The CHO advised that synthetic pyrethroids are also not known to be carcinogenic.
5.52
Advice from the World Health Organization in 2014 also suggests that community exposure to fogging with synthetic pyrethroids is considered safe:
The insecticide used in the mosquito fogging is a synthetic pyrethroid that is very similar to the insecticides used in most domestic insect spray cans that are found on supermarket shelves. The ‘fog’ is created by blasting the mixture of insecticide and water into very fine droplets through the fogging machine. The amount of insecticide in the fog is very small, and is dispersed at quantities that can only kill something as small as a mosquito, so at the concentrations used there will be no adverse health effects on people who are occasionally exposed to the fog. The type of insecticide being used in the fogger is also completely odourless.
5.53
The CHO stated that the products used in the City’s mosquito-control programs were unremarkable in the Australian context:
Millions of Australians reside in or visit areas with mosquito-control programs. Many of these programs are of a larger scale and have longer histories involving the use of older mosquito control agents. The department is not aware of any documented cancer clusters resulting from these programs.
Other chemical insecticides of concern to the community
5.54
Professor Fritschi told the committee that she was one of the experts who reviewed malathion in 2107, finding that malathion was ‘probably carcinogenic’. Professor Fritschi explained this meant that there was not enough evidence to be sure that malathion could cause cancer. She further advised that ‘malathion is not persistent in the environment’ and that, in any case:
… the levels in people who are in areas where malathion is being sprayed for mosquito control would be reasonably low.
5.55
Dr Drew detailed some exposure modelling conducted by the World Health Organization for fogging for mosquitoes using the organophosphate pesticide malathion, which found a ‘very low risk of exposure for bystanders’. Dr Drew also advised that ‘[m]alathion is regarded as being one of the least potent’ organophosphates.
5.56
Similarly, Professor Stewart advised that occupational exposure to malathion—by someone either manufacturing or applying the chemical product—would be the only scenario where levels of exposure might be high enough to pose a cancer risk.
Scientific consensus
5.57
Professor Stewart told the committee that the number of different types of cancer, along with the absence of any occupational exposure, strongly suggested that the cancers did not share a common cause.
5.58
Professor Fritschi also confirmed the general principle that cases of a specific type of cancer were more likely to share a common cause.
5.59
Dr Milne of Cancer Council Victoria advised the committee that there was no evidence either of a cancer cluster or of a common cause:
… when you're seeing people exposed to something in the community, you would expect to see a quite substantially elevated incidence of cancer and of specific cancers. … We didn't see evidence of either here.
5.60
Professor Stewart advised the committee that he had been unable to locate any evidence for the causation of cancer in any given population due to the historic use of chemicals in that community:
Has something happened at Bellarine with respect to the use of these agricultural chemicals that is quite distinct?' The answer, so far as I'm aware, is to the contrary—that is, if these chemicals cause cancer in latent populations because they were used historically, that must affect communities all over the world but certainly all over Australia. As far as I can see, there was no evidence that the circumstances in Bellarine are any different to those in most agricultural communities anywhere else—I could find no evidence of the causation of cancer by historic use of chemicals in any context …
5.61
Professor Stewart also stated that no comparable situations involving cancer causation had been documented:
… no closely similar situation of likely cancer causation under circumstances like those characterizing the Bellarine Peninsula cancer cluster has been reported in the medicoscientific literature.
Aggregate exposures
5.62
As mentioned above, Discovery 3227 believes that cancer and other illnesses in some members of the Barwon Heads community may have been caused by combined exposures to a number of chemical insecticides over time. Mr Harrison told the committee:
Over forty years the original Barwon Heads and Bellarine communities have been exposed to a long-term aggregate pesticide exposure …
5.63
Discovery 3227 submitted that spraying with a number of OPs and other chemical insecticides had, over time, led to illness and premature death for many community members, including a number of young people.
5.64
Dr Drew advised the committee that it was not possible for community members to have been exposed to more than one mosquito-control chemical at a time:
… the manner in which these chemicals are used to control mosquitoes is that they're not all used at the same time and they do not persist in the environment, and, therefore, exposure to multiple chemicals at the same time did not occur.
5.65
Professor Watterson told the committee that the historical use of fogging techniques meant that the exposures in question were likely to have been ‘immediate and acute’.
5.66
Dr Drew advised the committee that it was unlikely that aggregate exposure either to a single chemical or multiple chemicals would have increased the risk of cancer:
In terms of aggregate exposure, if you mean combined exposure to a number of chemicals at the same time, no. If you mean aggregate exposure in terms of a number of short-term exposures over a long time, for these particular chemicals, I believe not. These chemicals … don't interact with the DNA to cause mutagenesis.
Endocrine disruption
5.67
Discovery 3227 submitted that its concerns included certain endocrine-disrupting effects of the breakdown products of temephos, which it believes could have caused cases of cancer in the community.
5.68
Dr Jason Lutze of the APVMA advised the committee that temephos is considered safe when used according to the label directions. He also advised that the breakdown products of temephos, if it is used according to the approved label instructions, ‘would be at levels that wouldn’t be expected to cause harm’.
5.69
Discovery 3227 also expressed concern about endocrine disruption caused by exposure to chemical insecticides containing pyrethroids.
5.70
Professor Watterson told the committee about UK research which found that synthetic pyrethroids did not appear to carry a risk of endocrine disruption that could lead to cancer. Recent research reviewing studies in pyrethroid epidemiology found that ‘[t]oxicological testing on pyrethroids indicates a weak, if any, effect on the incidence of tumors’.
5.71
Similarly, Dr Drew advised the committee that: ‘these chemicals … don't interact with the DNA to cause mutagenesis.’
5.72
Professor Stewart, a professor in public health and the chemical causation of cancer, also advised the committee that endocrine disruption is not currently established as a cause of cancer. He stated:
I don't believe endocrine disruption is established as a definitive way in which cancer is caused, in the way that mutations through tobacco smoke in the lung is established. … As a general mechanism, I don't believe that in terms of environmental levels of chemicals, as distinct from chemicals administered as drugs, that endocrine disruption is established as a way of causing cancer.
Autoimmune disease causation
5.73
The department’s submission explained that the causes of different autoimmune diseases are not yet well understood:
… autoimmune disease is a broad category of diseases involving essentially any organ or system in the body, with different causes, pathways and treatments. …
The exact causes of autoimmune disease are not known; however, a range of risk factors have been identified that are likely to play a role in triggering the disease, including genetics, lifestyle and the environment.
Taken together autoimmune diseases are not uncommon and affect about five per cent of the population.
5.74
Research into the causes of autoimmune diseases continues. Some recent research has found that there is a strong genetic component to many kinds of autoimmune diseases, with a 2019 study finding that the risk of developing an autoimmune disease is ‘largely inherited’. A 2013 study, based on a systematic literature review and a meta-analysis, concluded that ‘shared genetic factors’ were the most likely cause of multiple autoimmune diseases occurring within the same family.
5.75
At a hearing, the CHO confirmed that autoimmune diseases are very common, telling the committee that:
Autoimmune diseases and inflammatory bowel disease are extremely common. I've got members of my immediate family with both of those illnesses.
5.76
The department advised the inquiry that the insecticides used by the City were not known to cause either cancer or autoimmune conditions, even during occupational use:
… none of these chemicals is known to cause cancer or autoimmune disease in humans during normal use by or for the public, or by workers when the product is used according to the label and with any recommended personal protection equipment for prolonged exposure to concentrated product …
5.77
The CHO later confirmed that there are no known links between the chemicals of concern and autoimmune diseases specifically:
None of the agents identified by Mr Harrison and Discovery 3227 have a demonstrated association with human autoimmune disease.
Further investigations
5.78
This section reviews the issues raised by submitters and other evidence to the committee about whether there are any further investigations that might be appropriate in the circumstances. The committee also sought expert scientific advice as to the feasibility and value of any further investigations into possible chemical exposures or the plausible causation of cancers or other illnesses on the Bellarine Peninsula.
5.79
Discovery 3227 and some other submitters suggested that further investigations would provide answers for the community. Discovery 3227 made several suggestions for further investigations, for example, a fixed retrospective cohort study and individual exposure studies. Discovery 3227 stated its belief that such further investigations would reveal ‘a cancer/immune cluster’.
5.80
The committee heard evidence from experts in the fields of epidemiology, public health, cancer clusters, chemical carcinogenicity (chemical causation of cancer), and toxicology and risk assessment. This evidence canvassed three possibilities:
a fixed retrospective cohort study;
a retrospective exposure study; and
no further investigations.
Fixed retrospective cohort study
5.81
Professor Fritschi explained to the committee that a fixed retrospective cohort study (FRCS) would identify a fixed cohort of people who were living in the area at a particular point in time and keep track of them and any cancer diagnoses in that cohort over time. When asked about any alternatives to a FRCS, Professor Fritschi advised:
I don’t think there is any other study design you could use that would give you an answer, but even the retrospective cohort study is probably unlikely to give you an answer that is really clear.
5.82
Professor Fritschi further advised the committee that a FRCS would require a larger population, the ability to locate all individuals who were possibly exposed, and information to determine the exposure dose each of them was historically exposed to.
… you would have to somehow go back in time and find all the people who lived there. You can't just do a call for anyone who lived in the Bellarine Peninsula, because that's likely to give you a biased result because people who are particularly interested in the question of cancer or autoimmune disease might be more likely to respond than others. So it is really important that you get everybody, and that's quite difficult to do.
5.83
Professor Watterson agreed that a cancer cluster population cohort study is difficult to implement, stating that ‘generally the problem is you lose people’.
5.84
Professor Fritschi’s advice to the committee was that, while a FRCS would be theoretically appropriate, it would be very difficult to implement in practice, and that, further, the population size was too small for such a study to deliver statistically significant results.
5.85
Similarly, Dr Drew advised the committee that he believed there was no benefit to a FRCS. However, he believed that a retrospective exposure study could be beneficial. He told the committee:
I think it's a lot easier to do some retrospective exposure modelling and ask the question, 'Were those exposures likely to cause health effects?'.
Retrospective exposure study
5.86
At the hearing on 20 November 2020, Dr Drew advised the committee that, in some cases, a retrospective exposure study could ask:
… what do we think the exposures were and were those exposures safe?
5.87
Dr Drew explained that this kind of study is based on:
… the information on how and how often the chemicals were applied, where they were applied, how far away from residences they were, how often people visited the actual places where the chemicals were applied and what the drift of the fog away from that area might have been. It's trying to determine what the exposures were. It's not a cohort study. It doesn't involve actually examining people. It involves examining the method of application.
5.88
John Curtin Professor of Epidemiology Lin Fritschi told the committee:
To do a study that would be statistically reliable and epidemiologically rigorous would be theoretically possible, but I don’t think it would be possible in real life because it is so hard to find all the people who had been exposed and to find the dose that they had been exposed to, and the numbers would still be low …
5.89
Dr Drew told the committee that this kind of exposure analysis is already used by the APVMA in its product evaluation process. He explained that this methodology also includes an additional safety margin by basing exposure estimates on worst-case scenarios:
… the use of mathematical modelling, which the APVMA use for a whole range of things when they evaluate pesticides, can give a good indication—albeit not necessarily the actual exposures but the worst-case assumptions for a number of different scenarios.
5.90
Dr Drew advised the committee that he thought that any exposures to community members such as bystanders ‘were likely very low’. When the committee asked whether he could indicate what levels of exposure could cause cancer, Dr Drew said:
… the answer is no, it is not possible to simply say how much an individual would need to be exposed over what period of time in order to be at a high risk of contracting cancer.
No further investigations
5.91
The Cancer Council Victoria report update of March 2021 used all available epidemiological data since records began. When asked by the committee about the value of additional epidemiological studies, the CHO advised that there was no benefit to be gained from any further narrowing of existing epidemiological analyses, and that this could, in fact, lead to greater uncertainty about the findings. He stated:
I do not believe, however, any further epidemiological studies, given their limitations, will be of any benefit to the community particularly because there is no known exposure to a hazard at levels known to cause cancer.
5.92
The Expert Advisory Group considered that any such analysis was ‘unlikely to be useful’ and, further, that it was ‘very unlikely’ to alter the findings of the March 2021 Cancer Council Victoria report update.
5.93
Professor David Hill, the chair of the Expert Advisory Group and an expert in cancer control science and cancer-related behaviours, told the committee:
Whilst it's nearly always possible to conceive of further research that might be undertaken, it's a matter of scientific judgement as to whether such research is feasible, capable of answering an important question and likely to benefit the community when concluded.
5.94
More categorically, Professor Stewart advised the committee that he believed there was no merit to any further investigations:
… in this particular case, rather than having a major problem, the fact that multiple cancers have been specified indicates that the matter can almost be resolved in a single sentence.
.… I could have simply said, 'Cancer clusters are inherently problematic and sometimes merit comprehensive investigation, but no authority in the world recognises as requiring thorough investigation cancer clusters that involve multiple tumour types, because every specific known carcinogen causes a particular group of cancers.'
5.95
Based on extensive experience in Australian cancer cluster investigations, Professor Stewart explained that a further investigation was highly unlikely to reveal a single cause for the cancers in question:
For the relatively few examples of cancer clusters which are subject to scientific investigation, unequivocal resolution of the matter may only be possible after years or decades. … scientific investigation almost invariably confirms that no recognized carcinogen(s) is responsible.
5.96
The Expert Advisory Group similarly advised that:
The EAG does not believe that further scientific studies of this perceived issue are justified or desirable.
Committee view
5.97
The committee acknowledges the difficulty of investigating cancer clusters and recognises that in most, if not all, cases such investigations can only result in a disappointing outcome for the individuals with cancer and their families and friends, who may be looking for answers that a scientific investigation cannot provide.
Information gaps
5.98
Based on the evidence received by the committee, the unfortunate reality is that it is almost impossible to comprehensively determine when, where and how individual chemical products were used in mosquito-control programs on the Bellarine Peninsula. There are many information gaps and some conflicting claims by submitters, and there is no mechanism for discovering all the details of chemical insecticide use by councils on the Bellarine Peninsula throughout the 1980s and 1990s.
Exposure to chemicals and disease causation
5.99
The committee notes that expert evidence to the inquiry suggests that any environmental chemical exposures for community members were likely to have been at very low levels that did not constitute a cancer risk. The committee further notes that, regardless of the actual chemicals used, evidence from experts suggests that the chemicals mentioned by submitters have no direct links to the diseases that have affected people in the Barwon Heads community. Furthermore, it appears that the hypothesis of aggregate exposures causing disease is not supported by the expert scientific evidence presented to the committee.
5.100
The committee notes that for some of the inquiry participants the difference between the carcinogenicity of a substance (cancer hazard) and the cancer risk to individuals, which is based on their personal exposure profile, is not well understood. The committee considers that this needs to be explained and communicated clearly to people who have expressed deep concerns about potential exposures to chemical carcinogens, as this difference is something that most people are not aware of, unless they have a scientific background.
Further investigations
5.101
As discussed in chapter 3, the committee notes that it is very difficult to assess a suspected disease cluster. The Potential Cancer Cluster Expert Advisory Group and the Victorian Department of Health both consider that the epidemiological and exposure concerns have now been addressed. They are of the view that the cases of concern to the community do not represent a cancer cluster, and that there is no scientifically plausible cause of cancer in the affected population.
5.102
The committee acknowledges once again that it does not have scientific expertise in epidemiology, toxicology or cancer causation. However, based on the scientific evidence received during the inquiry, the committee understands that any further epidemiological or chemical exposure studies would be of little value to the community. Importantly, the expert evidence provided to the committee identified concerns that any such further investigations would be methodologically unsound and would therefore lack scientific validity. The committee notes that these assessments are based on the current state of scientific knowledge as presented to the committee.
Recommendations to the Victorian Government
Communication and trust
5.103
The committee is of the view that the Victorian Department of Health did not sufficiently engage with individuals in the community to ‘establish the facts’ as the first step in its investigations into the fears of a cancer cluster or, more broadly, a disease cluster. Had it facilitated some form of individual input about concerns, rather than relying on the information available in media reports, this may have averted the mistrust and miscommunication that followed the Victorian Department of Health’s later responses to community concerns.
5.104
The committee believes it would therefore be highly beneficial if concerned community members could have the opportunity to hear from the Victorian Chief Health Officer in person about the latest epidemiological report findings and about whether any further investigations or other actions could or should be taken. This could be an opportunity to talk about the feasibility, scientific value and community value of any further investigations, and about whether there is any way to provide answers to those in the community who are still concerned about what has caused the development of cancer and autoimmune diseases in the Barwon Heads region. At the very least, this could give concerned individuals a better understanding of what a cancer cluster is, the data available and its limitations, and the difficulties shared by every investigation of a possible cancer cluster.
5.105
Importantly, in addition to meeting with concerned community members, the Victorian Department of Health should produce a detailed report that responds comprehensively, clearly and carefully to the concerns raised by the community. This would address current misunderstandings of scientific information and provide much-needed clarification on the cancer risks of the products used in past and current mosquito management programs throughout Victoria.
5.106
The committee agrees with the view of public health experts who believe that the successful outcome of a cluster investigation does not depend on proving or finding the cause of a cluster, but rather on reaching a satisfactory outcome for all groups involved. It is paramount to achieve a mutual understanding and the resolution of any conflict between the public’s expectation of a cluster investigation and scientific analysis within the limits of available data and knowledge. The Barwon Heads community deserves closure, and this can only be achieved through the active engagement of the Victorian Department of Health and Chief Health Officer in effectively communicating all the findings.
5.107
The committee recommends that the Victorian Government urgently undertake to:
prepare and release a comprehensive report which explains clearly and carefully the findings of the epidemiological studies and responds to the concerns in relation to chemicals used in mosquito management programs; and
meet with concerned community members at Barwon Heads to present the report and address any remaining concerns.
2004 Framework for mosquito management in Victoria
5.108
The committee notes that the 2004 Framework for mosquito management in Victoria appears not to have been reviewed or updated since 2004, although its update frequency is listed as ‘annual’. This state-level policy document should be reviewed and updated to reflect the current regulatory environment and current mosquito-control practice across the state.
5.109
The committee recommends that the Victorian Government review and update the Framework for mosquito management in Victoria published by the Victorian Department of Sustainability and Environment in 2004.
Role played by the media
5.110
The committee notes with concern the role played by the media, especially from late 2018 until October 2019 when the Senate inquiry began. The committee is aware that media coverage of cancer cluster investigations is often framed in simple language that obscures the scientific reality that true ‘clusters’ are extremely rare. More recently, some media reports about the latest epidemiological study released in April 2021 were misleading and did not fully reflect the nuances and caveats that needed to be applied in relation to some of the data. Media organisations and journalists have an important role to play in highlighting community concerns; however, there is a need for scientifically correct content in circumstances where there is concern about the incidence of cancer in a community.
Concluding comments
5.111
The committee thanks once again the private individuals who came to share their experiences. The committee recognises that the inquiry process was long and emotionally draining for many individuals. The committee regrets that the COVID-19 situation delayed the inquiry process.
5.112
It is hoped that this report provides more clarity to all those affected in the Barwon Heads community.
5.113
Finally, the committee recognises the significant impacts that cancer and autoimmune diseases have on the community and acknowledges the concerns raised by residents about the incidence of these diseases in the area.
Senator Rachel Siewert
Chair