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An experience report from an expert's perspective
In spring 2024, Ecosens AG was contacted by a gentleman who owns a farmhouse with an attached barn in the Winterthur region. This is his parents' house, where he grew up. According to his memories from his childhood, the entire woodwork of the barn had been treated with wood preservatives (HSM) in the 1960s to prevent infestation with longhorn beetle and other pests. This had led to the "poisoning" of milk and hay and even to health problems, including stillbirths among the cows. As a result of the treatment with HSM, the milk had to be disposed of in the slurry pit or even incinerated.
The barn and the adjoining residential building are in a largely unchanged condition since the 1960s. The residential building is currently occupied by a relative.
The owner approached Ecosens AG with the question of how the house and the barn could be used in the future. The options are either to renovate the building and convert the barn into living space or to demolish the building. It needs to be clarified whether there is still evidence of wood preservative contamination in the building structure decades after the presumed treatment. The results of the investigation should serve as a basis for the decision regarding the future use of the building.
If the use of HSMs is suspected, the contamination situation can be determined quickly and cost-effectively by taking material samples from the wooden components and sampling the lying dust. Due to their physical properties (low volatility), HSMs usually accumulate in dust. Dust is therefore an ideal medium for testing the suspected use of HSMs.
For this reason, the expert took six material samples from the beams of the barn and the attic of the residential building in spring 2024. As it was to be expected that the HSM treatment was superficial, wood shavings were planed off. In addition, a mixed sample of the lying dust was taken from the barn.
During the on-site inspection, the owner was questioned intensively about the alleged treatment of the barn. He was able to vividly reconstruct the events of the time from his memory.
Following the on-site inspection, the customer searched through his parents' estate again and was able to provide Ecosens AG with various documents from 1967 - 1972. These clearly show that the building was treated with insecticides and that the hay and milk were heavily contaminated as a result.
From the expert's point of view, the question arose as to whether the preventive and systematic treatment of the barn with insecticides was an isolated case, which is why a literature search was carried out in publicly accessible newspaper and magazine archives. During the research, documents were quickly found that show that the large-scale treatment of barns with wood preservatives was widespread in the 1960s. The following section is based on an article on plant protection and the environment published in 1972 in the Swiss Journal of Forestry [1] and an interpellation by Curt Signer (Cantonal Councillor of the Social Democratic Party) of February 3, 1969 on pesticide residues in food in the Cantonal Council of the Canton of Zurich [2].
In the spring of 1968, a scandal broke when the USA rejected and returned Swiss export cheese due to excessive pesticide residues. The Swiss Federal Research Institute in Wädenswil (now Agroscope) was commissioned to identify the sources of contamination. Thanks to the active cooperation of cantonal laboratories and industry, the most important source was identified by the fall of 1968.
From the 1950s onwards, the twice-yearly whitewashing with milk of lime or simply cleaning the stables, as stipulated in the 1936 Foodstuffs Ordinance, was increasingly carried out using chemical agents, such as the product "Pintox". This was a barn fumigant with added insecticides (DDT, Dieldrin, hexachlorocyclohexane or lindane), which was used in most barns in many municipalities on the recommendation of the dairy associations. The insecticides contained in the barn whitewash all belong to the group of organochlorine pesticides. DDT and lindane are probably familiar to most readers. The use of dieldrin as a wood preservative, on the other hand, is less well known. Dieldrin is a highly effective insecticide that was frequently used as a contact and feeding poison against insects. It is highly likely to be carcinogenic and, like other organochlorine pesticides, is persistent (degrades very slowly) and accumulates in organisms (bioaccumulative). The aim of the use of "Pintox" was the preventive and occasionally also acute control of house longhorn beetle in the roof timbers of barns and residential buildings.
Curt Signer explained this in his interpellation in 1969: "It borders on negligence when you know that these toxic agents were sprayed in the barns without sufficiently covering the stored hay stocks. In the canton of Zurich alone, around 100 barns were treated in this way last year. Today we can only marvel at the lack of concern of the chemical factories responsible and the far too long hesitation of the scientific experts. It is a well-known fact that one wood impregnation company in particular was able to paint the farmers the white sky and convince them of the necessity of such barn treatments, one of which cost nota bene 10,000 francs."
According to his recollections, it happened exactly as described above in our client's parents' house. In 1967, his parents were visited by two representatives of a building protection company who inspected the barn. Due to a small-scale infestation of wooden beams, the representatives recommended treating the entire barn and the attic of the adjoining house with insecticides. According to the original order confirmation in our possession, the costs for the treatment of the house and barn amounted to CHF 10,600. This was a considerable amount at the time, as the average annual salary in 1967 was around CHF 16,000.
The wood preservative contamination can enter the cows and thus the milk via various routes. In addition to direct ingestion by licking treated wood and inhalation of contaminated barn air or dust, ingestion occurs primarily via feed stored in the barn, such as hay. Particularly problematic is the fact that, especially in the hot summer months, the active substances outgas from the wooden beams and quickly contaminate the freshly stored hay. When the dairy cattle are fed hay again in the fall and winter, the contamination of the milk also increases and reaches its highest levels in the spring.
Various protective coatings were tested to prevent the wood preservatives from blooming and evaporating. According to studies by the Wädenswil Research Institute, however, all of these tests failed to produce positive results, as it was proven that the active substances were able to penetrate all protective layers and thus poison the feed supplies anew. It was also shown that the contamination of the hay and thus the milk only decreased very slowly over several years. For example, a farm in a community in Zurich supplied milk with a dieldrin content of 140 ppb in the fall of 1968 and still 120 ppb in the fall of 1971, i.e. after three full years. The toxicological limit for dieldrin in milk at that time was 5 ppb and was therefore exceeded by a factor of more than 20 on this farm.
As long as heavily contaminated milk flows into a large milk stream and is diluted with uncontaminated milk, there is no immediate danger to humans. However, if the contaminated milk from the farm is consumed for personal use, the tolerance limit is clearly exceeded. Curt Signer states: "It is obvious to everyone that children in particular are directly at risk here, especially as it is now known that even dairy animals have been made ill by insecticides."
The documents provided to us by the client make it easy to trace what happened on his farm. After the insecticides were applied in 1967, the hay in the barn was examined in February 1969 by the then Zurich cantonal chemist Dr. Ernst Roman. The hay lying against the outer wall of the barn showed high concentrations of lindane and dieldrin of up to 50 mg/kg. It was therefore decreed that the hay must not be fed under any circumstances and must be removed and burned.
In April 1969, a decree was finally issued regarding a milk ban. It stated that the milk was to be denatured with a dye under the supervision of the health authorities until it was clearly colored and then disposed of in a harmless manner (septic tank). In mid-1970, the milk was tested again and, due to the high levels of contamination, was again banned from consumption or feeding until more "favorable" test results were available. In addition, an order was issued in 1970 that no more hay could be stored in the barn until further notice due to the contamination. The corresponding letter came from the Winterthur Milk Association. It was addressed to "association members whose barns have been treated against house longhorn beetle". It therefore appears that various other farms in the Winterthur region were affected.
These incidents were a factor in our client's parents ceasing agricultural activities on the farm in 1973. A court case brought by his parents against the building protection company was unsuccessful. One of the main reasons for this was probably the fact that the company had an official permit to dispense these wood preservatives from the Directorate of Public Health of the Canton of Zurich (document available to the expert).
As a result of this crisis, in spring 1970 the Swiss Federal Research Institute in Wädenswil asked the Federal Office of Public Health to ban the use of a whole range of chlorinated hydrocarbons in households and industry. The use of wood preservatives containing dieldrin, aldrin, lindane and DDT was banned when the ordinances to the Federal Poisons Act came into force in 1972. Pentachlorophenol (PCP), on the other hand, was used as an active ingredient in wood preservatives until the 1980s. Products containing such active substances were still allowed to be manufactured, sold or imported in Switzerland until 1989
Based on the information and documents received since the sampling, the analysis results of the material and dust samples from our customer's barn and home were eagerly awaited. The legitimate question arose as to whether wood preservatives could still be detected in the samples some 55 years after treatment.
In fact, the wood preservatives dieldrin and lindane were detected in elevated concentrations in all the samples taken. The concentration of dieldrin was in a very similar range of 20 - 26 mg/kg in all samples, including the dust sample, while the concentration of lindane was slightly lower at around 3.3 - 13 mg/kg. In addition, low concentrations of DDT and PCP were detected in some samples (< 2 mg/kg). Interestingly, with the exception of a single beam, no white coatings were visible that would visually indicate whitening or contamination with wood preservatives.
We have no information on the contamination of the wood with dieldrin and lindane shortly after treatment. Since the hay stored on the exterior wall in 1969 was contaminated with 50 mg/kg dieldrin, it can be assumed that significantly higher concentrations were present in the wood shortly after treatment. Nevertheless, this study impressively demonstrates the low degradation or release rate of wood preservatives in buildings, as even 50 years after surface application, significantly higher levels of contamination can still be detected. The very homogeneous contamination situation of the wooden beams shows that all exposed surfaces of the barn were actually treated at that time.
After these analysis results were sent to the client, the client asked the crucial question of what the proven contamination meant for any further use or demolition of the barn. Answering this question is not trivial. In Switzerland, there are hardly any explicit regulations regarding the handling of buildings with HSM contamination. Reference is therefore usually made to the German PCP guideline [3]. It is assumed that the guideline values for PCP specified therein can also be applied analogously to other chlorinated hydrocarbons (e.g. lindane or DDT).
In our view, the following applies if the barn is demolished:
According to the Ordinance on the Prevention and Disposal of Waste (VVEA), wooden beams coated with organohalogen compounds (such as HSM) are considered problematic wood waste and must be disposed of thermally in an authorized waste incineration plant (KVA) or in a cement plant. However, a limit value (> 5 mg/kg) is only specified for PCP for classification as problematic wood waste (VVEA, Annex 7, Paragraph 2). There are no explicit limit values for other wood preservatives. According to common practice, however, contamination with comparable HSMs such as lindane, DDT or dieldrin is usually assessed analogously.
Nevertheless, it must be noted that according to the VVEA, only analyses for PCP are prescribed prior to the disposal of wood. In the object in question, the concentration of PCP was a maximum of 0.2 mg/kg. If the wood had been analyzed for the individual substance PCP, it would have been classified as untreated according to the VVEA and could have been sent for recycling.
In addition to demolition, the owner is also considering converting the barn into living space. This raises the question of whether the contamination detected in the wood could lead to a potential health risk for future occupants. This question could not be answered conclusively for the client on the basis of the results of the investigation.
To assess a possible health risk, it is necessary to carry out indoor air measurements and then compare them with toxicologically derived guide values. However, when barns or attics are converted into living spaces, the air exchange rate is usually drastically reduced. This means that based on air measurements in the currently uninsulated and heavily ventilated barn, no qualified statements can be made about possible future indoor air pollution after the conversion. For this reason, air measurements were not carried out in the current phase.
The assessment values according to ecobau can be used for the indicative assessment of HSM contamination in house dust and material samples. Exceeding the intervention value means that remediation must be carried out immediately. After remediation, the exposure should not exceed the remediation target value in order to rule out a health risk.
With maximum concentrations of 26 mg/kg in wood and dust, the intervention values according to ecobau are undercut in this property. However, the remediation target values are clearly exceeded. If the values are between the intervention and remediation target values, the pollutant situation should be improved for precautionary reasons so that the remediation target value is ultimately achieved as far as possible.
In the report, the customer was informed that additional investigations into the contamination situation would be necessary in the event of a planned renovation (e.g. determination of HSM penetration depth). However, based on the available results and the full-surface treatment of all beams, it can be assumed that professional remediation of the wood preservative contamination will most likely be required as part of a renovation. The depth of the remediation measures depends on the planned subsequent use, the presence of exposed wooden beams in living spaces, the air exchange rate and other factors and cannot currently be estimated precisely.
This practical example shows what consequences the uncritical use of chemicals can still have decades later. From our point of view, the following conclusions can be drawn:
Even 50 years after the ban on various organochlorine pesticides, such contamination is still relevant. According to the report on plant protection and the environment [1], several hundred barns were contaminated with wood preservatives during these "barn whitewashing campaigns". In addition, wood preservatives were also used preventively or after an infestation in many other buildings or attics. Older buildings with a relevant proportion of wooden components should be systematically tested for wood preservatives, particularly if a change of use is planned.
By taking material or dust samples, the use of wood preservatives in the building can usually be detected quickly and cost-effectively. When taking material samples, however, it is important to ensure that composite samples are always taken from several beams. This reduces the risk of a false negative analysis in the event of local treatment of individual beams. As wood preservatives accumulate on dust particles and these are subsequently distributed indoors, HSMs can usually be detected in dust samples even when applied locally. Further specialist knowledge is required to carry out air measurements. The measurement conditions (temperature, air exchange, etc.) have a decisive influence on the results.
According to the VVEA, wooden components must be tested for PCP before disposal or reuse. There are no binding specifications for analysis prior to conversion work. In our experience, the wood is usually tested for PCP, lindane and DDT. However, the investigations and research presented here show that dieldrin and possibly other insecticides were also used extensively in Switzerland. Especially when barns or attics are converted into living space, a comprehensive analysis program is recommended to exclude a possible health risk, which contains at least Dieldrin in addition to PCP, Lindane and DDT. This can prevent contaminated wood from posing a potential health risk in inhabited interior spaces or from being recycled into building materials.
Bibliography:
[1] Bosshardt, H.-P. (1972). Plant protection and the environment. Swiss Journal of Forestry, Volume 123, Issue 10. Available at: https://doi.org/10.5169/seals-765074
[2] Interpellation Curt Signer - Wädenswil of February 3, 1969 on pesticide residues in foodstuffs, StAZH MM 24.78 KRP 1969/063/0483
[3] ARGEBAU (1997). Guideline for the assessment and remediation of pentachlorophenol-contaminated building materials and components in buildings (PCP Guideline). Version October 1996
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