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Use environmentally adapted hydraulic fluids

In the 1980's new hydraulic fluids were developed for the forestry industry. The health issues associated with the traditional mineral oil based lubricants enhanced this development. Users suffered from eczema, oil acne, oil blackheads, respiratory irritation and also from the unpleasant odour of the oils. Environmental problems were also observed. Mineral oil can spoil the taste and smell of groundwater in concentrations as low as 1 ppm (parts per million) (1)(2)(3).

The hydraulic fluids based on mineral oils contained viscosity improvers (polymethacrylates) in quantities up to 20%. In tests on such oils, 9 out of 13 machinery users developed skin irritation (4). Such products could only be released on the market because there simply were no regulations covering the composition and properties of hydraulic fluids.


High consumption
Motor oil is the only lubricant sold in greater quantities than hydraulic fluid in Sweden. The total annual consumption in recent years of hydraulic fluids, has steadily been just over 30 000m3 (5). One of the main contributors to this high consumption is the forestry industry. In practice, the quantity of oil used in hydraulics is considerably higher than the figure above, because many people use cheap motor oil (especially in old machinery).

Despite improvements in recent years, large quantities of used hydraulic fluids are not recovered for proper disposal. It is expensive to properly dispose of waste oil and many people just 'top up' when the fluid level is low. Considerable quantities finally end up in the environment.

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Rena Smörjan - Clean lubricants
In 1992 the Swedish Chemicals Inspectorate published a comprehensive chemical, technical and toxicological assessment of lubricants ('Rena Smörjan', KemI Report 8/92 ). One important conclusion from the report was that the situation with hydraulic fluids is especially alarming. This was based on the large flow of the oil into the environment combined with poor biodegradability and also the uncontrolled addition of health and environment threatening additives.

The 'Ren Smörja' project started in Göteborg Sweden, where, in consultation with the forestry and haulage industry, a model was drawn up for a fluid that was better for health and the environment which did not compromise performance. The biodegradability of the oils and the toxicity of both the oils and the additives were considered to be the most important factors for health and the environment. Oils where a high proportion of the mixture originated from renewable sources were also favoured but this was not one of the main assessment criteria.

These criteria were later used as a basis for the voluntary environmental requirements in the Swedish technical standard for hydraulic fluids SS155434.


All oils are damaging to the environment. Oils can cause long term damage and also exert direct physical effect. The concentration of oil compounds in the sediment around the Swedish coastline has increased over the last few decades. This accumulation is mainly due to general, constant use of oil products (90%) rather than from major accidents (2)(7),

The oil that ends up on beaches and seabeds can cause extensive damage in concentrations of just a few grams per m3. The oil changes the properties of the sediment, rendering it unattractive for flora and fauna. Oils biodegrade especially slowly in the cold Swedish climate (2)(7)(8).

In reality, many factors influence the rate of biodegradation of oils in nature. However, in a report recently published by the EU, so-called environmentally adapted oils were found to biodegrade between 3 and 10 times faster than traditional mineral oils (9).

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Toxic additives
Hydraulic fluids contain a range of performance-enhancing additives to minimise oxidation, engine wear, corroision, foaming and to improve viscosity and to lower the pour-point. In conventional fluids many of these additives present a risk to health and the environment. Some are sensitizers, skin irritants, carcinogens or toxic to other organisms in the environment (6).

The voluntary environmental requirements in the Swedish standard has lead to a strong reduction in the use of high-risk additives. The standard has been a major contributing factor to the fact that international additive manufacturers have developed alternative, effective additives which carry a much lower risk for humans and the environment.


Used oils
Whether 'green' oils really are environmentally adapted was recently questioned in a newspaper article. The main basis for the article was a toxicological study of the changes undergone by hydraulic fluids during use. The study was undertaken by Västerås Petroleum AB (10).

The study suffered from a number of shortcomings and unclarities. The toxicological results (Mikrotox) were reported at different pH values. The bacteria in the test are extremely sensitive to changes in pH and if the pH has not been regulated in the study then the results simply cannot be interpreted or compared.

Another observation in the study worth noting is that that only copper was investigated, despite other toxic substances being present (zinc, calcium sulphonate). The presence of these substances suggests that motor oil or conventional hydraulic fluid was present in the mixtures tested. All of the oils tested showed high toxicity both before and after "ageing" with the exception of one of the environmentally adapted fluids that was found to have lower toxicity after "ageing" despite higher copper concentrations.

The study raises a number of questions: How much relevance do laboratory-based, clearly 'home-made' ageing tests have to reality? Why is a non-standard toxicity test chosen and was that test correctly carried out? How is it that several environmentally adapted fluids were found to be contaminated with motor oil or conventional hydraulic fluid? How is it that metals that should not even be present increase in concentration during the ageing process?

In summary, this study has such serious scientific shortcomings that no general conclusions can be drawn from the material. Other comprehensive studies undertaken on environmentally adapted fluids used under actual working conditions show the opposite result - little change over a long period of use (11)(12)(13).

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The function is important
Problems arose when environmentally adapted hydraulic fluids were first used in forestry machinery in the 1980's. Leaking seals, oil spills which hardened in sunlight on the machinery, immiscibility issues - especially with motor oils, the water content of the fluid rose and in some case machinery components were even damaged.

The forestry industry set up a group made up of representatives from the major forestry companies and commissioned machinery experts to jointly study what the sources of the problems were and how they could be mitigated. This group also included haulage industry representatives. Contact was made with the machinery manufacturers and oil suppliers in an attempt to improve the situation.

One by one most of the problems described above have been solved and after 15-20 years on the market, almost 90% of hydraulic fluids used in forestry are environmentally adapted oils. This result could not have been achieved if the products were not up the standard of conventional oils.


Correct handling
Environmentally adapted fluids are somewhat more sensitive to water than conventional hydraulic fluids and it is important that they are not mixed with motor oils. Old forestry machinery that have run on mineral oils for many years can develop leaky seals if environmentally adapted fluids are used instead. This is mainly due to the fact that environmentally adapted fluids are part of a new generation of products whose properties differ from those of the mineral oil. They require new knowledge in order to handle them in the best way so to ensure that problems don't arise.

According to Sören Bergek, manager responsible for machinery technology at the large forestry company SCA Skog in Sundsvall, Sweden: "The products work well now that everyone has learnt how to handle the oils' properties. That involves choice of fluid and checking the condition of the oil amongst other things. This type of product is here to stay and other lubricants and oil products will go through the same environmental adaptations in the future".

A Finnish study found skin irritation problems amongst forestry machinery operators compared to a control group. These skin problems were mild and no correlation was found with which type of fluid was used (14). Another Finnish study concluded that environmentally adapted fluids caused skin irritation, but the examining methods proved to be questionable (15). However, it must be pointed out that no hydraulic oils are good for skin and one should protect skin from contact with all types of hydraulic fluids.

In the second study mentioned above, a dramatic increase in motor and machine damage is claimed to have occurred, due to environmentally adapted fluids. After making direct contact with a large number of oil companies and the major machinery manufacturers, this could not be confirmed.

The machinery manufacturers said that they had no issues to raise with the environmentally adapted fluids, which they use in their new products, and which come with a guarantee. Most oil companies said that they were not aware of any increased machinery damage due to environmentally adapted fluids either. Few complaints had been received regarding these oils. Where is the scientific documentation of the dramatic increase in damage?

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Choose the right kind of environmentally adapted fluid
Environmentally adapted fluids can have very different compositions. They can be made from purely vegetable-based esters, synthetic esters based on vegetable or animal fatty acids, or from synthetic esters based on petroleum products. The composition affects the technical properties of the oil.

The so-called 'SP list' of approved environmentally adapted hydraulic fluids can give the impression that also performance is tested and approved by SP. This is not the case; rather it is the manufacturers' responsibility to ensure that the oils fulfil the technical requirements. A complementary study that checks that an oil is appropriate for a particular use is undertaken by some machinery manufacturers and haulage companies these days. There are environmentally adapted fluids on the market today that well match the technical standards of mineral oils and that meet the high demands on function and stability.


Follow the forestry example
If the health and environmental requirements on hydraulic fluids are dropped then there is a risk that 20 years of positive development will be lost and the market will be open to cheap, poorly biodegrading oils with additives that risk human health and the environment. A bad alternative!

Why not follow the example set by the forestry industry instead and gather the haulage and machinery industry to try to define the problems that their branches have with environmentally adapted fluids. How does one resolve these issues together and which environmentally adapted fluids best suit the equipment used in these branches?

Jan Ahlbom | Environmental Engineer, Västra Götaland County Administration
Ulf Duus | Toxicologist, Ren Smörja Project
Göran Värmby | Project manager, Business Region Göteborg

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(1) Gellerstedt, S. 1988. Hydrauloljor i skogsmaskiner: Kemi - Hälsorisker - Skydd. Sveriges Lantbruksuniversitet, Institutionen för skogsteknik. Uppsatser och resultat nr 102.

(2) Petterson, I. Broman, D. 1990. Effekter av kontinuerliga utsläpp av olja till den akvatiska miljön. SNV Rapport 3697, Stockholm.

(3) Central Institute for Water and Food Research: Compilation of odour threshold values in air and water. Zeist, Holland.

(4) Carlson, I. 1983. Anförda hudbesvär pga hydraulolja hos SCAs maskinförare anslutna till Skogshälsan i Boden.

(5) Statistik från Svenska Petroleum Institutet(SPI).

(6) Ahlbom,J. Duus,U. 1992. Rena Smörjan. Smörjmedel - möjlighet till förändring. KemI Rapport 8/92.

(7) Lindén, O. 1992. Oljeskador Miljö A till Ö. Svenska Folkets Miljölexikon, pp 198-199. Det Naturliga Steget, Bokförlaget Bra Böcker, Nationalencyclopedin.

(8) SOU. 1998. Att komma åt oljeutsläppen. Betänkande av olje-utsläppsutredningen. Kommunikationsdepartementet. Sthm.

(9) European Commission. 2003. Technical Guidance Document on Risk Assessment. Part II. European Chemicals Bureau.

(10) Arvidsson, L. 2003. Studie av hydrauloljors egenskapsförändring från oanvänt till använt tillstånd med speciell fokus på giftighet. Västerås Petroleum Kemi AB.

(11) Viktor et al. 1997. Miljöfarlighetsbedömning av hydrauloljor för arbets- och skogsmaskiner. IVL-rapport B 1267.

(12) Värmby, G. Duus, U. 1994. Ren Smörja i Göteborg - fälttest av hydrauloljor. Miljönämnden, Göteborg Stad.

(13) Battersby et al. 2003. Environmentally Acceptable Hydraulic Fluids - Field performance in mobile equipment. Shell Global solutions, United Kingdom

(14) Kallunki et al. 2002. Exposure to and health effects of chemical and biological agents in mechanical wood harvesting. Kuopio Regional Institute of Occupational Health. Finland

(15) Svensk Maskinprovning. 2003. Miljöanpassade oljor - är dom farliga? Litteraturstudie av Louise Johansson., SMP, Umeå.

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ansvarig utgivare: projekt GRÖN KEMI