1 

Comparative environmental fate of 

marine lubricants 

Stephen M Mudge 

Exponent UK 

Harrogate 

HG2 8RE 

UK 

CONTENTS 

Summary................................................................................................................................................. 2

1. Introduction to Marine Lubricants ...................................................................................................... 4 

Base oil types....................................................................................................................................... 7 

2. Assessment Approach.......................................................................................................................... 9 

Additives ........................................................................................................................................... 10 

3. Degradation and Biodegradation of Base Oils .................................................................................... 11 

Alkanes in Lubricants ..................................................................................................................... 11 

Polyalphaoelfins (PAOs) in Lubricants ............................................................................................ 13 

Polyalkylene (PAGs) and Polyethylene Glycols (PEGs) in Lubricants ................................................ 13 

Esters in Lubricants........................................................................................................................ 14 

Testing for Biodegradation of Marine Lubricants ............................................................................... 17 

Degradation & Biodegradation: Conclusions...................................................................................... 20 

4. Toxicity.............................................................................................................................................. 22 

Testing for Toxicity of Marine Lubricants ........................................................................................... 22 

Toxicity - Conclusions ........................................................................................................................ 23 

5. Bioaccumulation................................................................................................................................ 25 

Testing for Bioaccumulation of Marine Lubricants ............................................................................. 27 

Bioaccumulation - Conclusions .......................................................................................................... 27 

6. Additives in Marine Lubricants........................................................................................................... 29 

7. General Conclusions .......................................................................................................................... 30 

References ............................................................................................................................................ 34 
2 

 Summary 

Lubricants are used to reduce the friction between surfaces, reduce corrosion and isolate metal surfaces 

from water. They are extremely important for the safe and effective operation of most machines, 

including those found on board ships. The use of lubricants on board ship often results in the lubricant 

entering the sea through wash off, discharge, spills or leaks. These small, but frequent inputs result in a 

significant amount of chemicals entering the sea on an annual basis (estimated 38-62 million litres per 

year). The lack of legislation controlling these inputs and the nature of these chemicals can result in 

potentially persistent, bioaccumulative and toxic chemicals entering the marine environment and the 

food chain. To reduce the environmental impact of these inputs it is important to understand the 

chemical and biological processes these chemicals undergo in the marine environment and use this to 

select components with the lowest possible environmental impact. 

According to the American Petroleum Institute (API), the base oils, the major component of lubricants,

can be made from petroleum or oleochemical (biological) sources with >95% of the market currently 

dominated by the petrochemical sources. The oil can be simple fractions from refined crude oil or be 

synthesised from monomers provided by the petrochemical industries. Biologically sourced oils tend to 

be from vegetable seed crops in the form of esters.

The biodegradability of the base oils depends on the chemical formulation with many of the mineral oil

components including alkanes having the slowest rates while the esters have the fastest rates of 

removal in the OECD tests. The single end points in the OECD tests at 28 and 56 days are not sufficient 

to differentiate between some oils as the initial rate and proportion that is ultimately degraded may be 

missed. Naturally occurring marine organisms are able to degrade many oil constituents although the 

time taken to complete the process is dependent on the induction of enzyme systems. The degradation 

rate of the base oil depends to an extent on the presence of oxygen in the constituent molecules which

also increases the water solubility of these chemicals. 

Chemicals are taken up by organisms (bioaccumulated) in the marine environment with those 

compounds that are least water soluble being more readily accumulated. The process is called 

bioaccumulation and will depend upon the environmental and biological half life of the compounds; 

those chemicals that degrade quickly will not bioaccumulate to any great extent. In this regard, the 

mineral oil components are accumulated to a greater extent than the esters which also degrade the 

fastest. Switching to base oils that are more water soluble, degrade faster and have larger molecular 

weights will all serve to reduce the bioaccumulation potential. 

Some chemicals are inherently toxic and the base oil components will exhibit a degree of toxicity 

towards marine organisms. The magnitude of this toxicity is also dependent on the fraction or cut of 

mineral oil used in the lubricant products. Those containing aromatic hydrocarbons such as unrefined or 

partly refined crude oil will have an inherently higher toxicity. In general, however, all crude oil derived 

fractions have the higher toxicity than those derived from oleochemicals. 

The nature and quality of the base oil will also determine which compounds need to be present in 

addition to the base oil to ensure a suitable performance during use. These additives may only be 
3 

present in small amounts but may be toxic. Minimising the use of additives through choice of good 

quality base oil or through switching to non-toxic additives would also be desirable. 

On the basis of the three categories, degradability, bioaccumulation potential and toxicity, the mineral 

oil derived base oils have the greatest environmental effects; they also currently have the largest share 

of the marine lubricant market. In contrast, the oleochemical base oils only make up a small part of the 

current market although their environmental impact will be significantly lower. Reduced marine 

environmental effects may be achieved through a shift in the choice of base oil from petroleum derived

to oleochemicals. 

Irrespective of whether a base oil is mineral oil or oleochemical based, its environmental characteristics 

should be assessed to ensure base oils with the best environmental performance are selected. This is 

equally true for the additives used in lubricant formulations. A small concentration of highly toxic 

additive may completely change the toxicity of the final lubricant. It is therefore important to assess the 

marine biodegradation, bioaccumulation and toxicity of all base oils and additives within a lubricant 

formulation to ensure that components with the best environmental performance are selected. Test 

methods that mimic the marine environment must be used to ensure representative testing is carried 

out. 
4 

1. Introduction to Marine Lubricants 

Concerns about the environmental impacts of lubricants used at sea are growing but as yet there is no 

international legislation in place to monitor or control operational discharges of lubricants in the open 

ocean. The International Maritime Organization (IMO) recommends lubricants with high 

biodegradability for Arctic seas, while under the OSPAR Convention for the North East Atlantic offshore 

industry, including oil and gas platforms, lubricants must meet environmental standards under the 

HMCS (Harmonised Mandatory Control Scheme) programme. There are no such standards for the 

shipping industry and, in general, no discharges are recorded unless a prosecution for a large scale 

spillage is made. 

According to industry figures, the total global market for marine lubricants is around 2.8 x 109 litres per 

year and this can be broken down into the various sectors as shown in Table 1. 

Table 1. Annual Sales of Lubricants by Sector / Type. 

Lubricant Usage Volume 

(x103 litres) 

Cylinder Oils 1,500,000 

System Oils1 400,000

Trunk Piston Eng. Oils (HFO) 580,000

Marine Diesel Oils (Gas Oil) 180,000

Multi-Grades 25,000 

Hydraulic Oils 100,000

Mineral Gear Oils 30,000 

Synthetic Gear Oils 2,000 

Synthetic Compressor Oils 4,000 

Mineral Compressor Oils 3,000 

Turbine & Heat Transfer Oils 15,000 

Refrigeration Oils 2,000 

Greases 8,000 

Others 2,000 

Total 2,851,000 

1

 Stern tube oils tend to be engine oils (~90% of the total) with dedicated stern tube oils only used when 

leaks are occurring from the seals. 

Etkin (2009) reported that between 38 – 62 x 106 litres of lubricant are lost to the environment1 each 

year with a significant proportion occurring in ports and harbours; the remaining losses occur while the 

vessels are underway and the lubricants are lost to the open ocean and coastal seas where they are less 

 

1

 See Appendix One: Lubricant pathways from shipping to the Marine Environment 
5 

visible. The environmental impact will usually be less offshore as there are fewer organisms for the 

compounds to come into contact with and the benthic region may be many kilometres away. The larger 

body of water also means that compounds can be widely dispersed which aids in the degradation 

process. 

The difference between the total market for lubricants (2.85 x 109 litres, see Table 1) and the 

environmental losses (~1.2 x 108 litres, (Etkin, 2009)) suggests that 2.7 x 109 litres (95%) are “consumed” 

annually, with a proportion being recycled or reused as something else (e.g. fuel) with the rest being 

converted to a product (e.g. CO2) by processes such as combustion. In a wide ranging review of oil 

entering the marine environment, the Joint Group of Experts on the Scientific Aspects of Marine 

Environmental Protection (GESAMP) indicated that some small two stroke engines e.g. those used on 

small fishing and leisure vessels, may emit up to 25% of the fuel – lubricating oil mixture while running 

(GESAMP, 2007). Combustion will produce unburned hydrocarbons, partially oxidised products and soot 

which enter the marine environment through atmospheric deposition from stack emissions or direct 

injection with sub-surface exhausts. Outboard motors using the two stroke principle only make a small 

contribution to the total overall impact compared to other sources. Large two stroke marine engines, 

such as those used on container ships and tankers, are inboard and their exhaust is through the main 

stack of the ship although unburned hydrocarbons may be rained out or washed out of the atmosphere 

into the sea as well. 

The mechanism by which oil or lubricant gets into the water will play a major part in determining its 

impact upon the species found within the sea. Oil or lubricant dispersed below the water line may prove 

to have a more toxic effect than if spilled on the surface due to its greater availability to organisms, 

particularly filter-feeders such as shellfish. Oil or lubricant in a separate layer on the surface may have 

fewer impacts on these species unless transferred on to the shore (particularly mudflats) by tidal action. 

Evidence of operational ship pollution in the Irish Sea and Anglesey 

Evidence of oil losses during normal operations can be seen in Figure 1. In this example, Advanced 

Synthetic Aperture Radar satellite images of the Irish Sea and Anglesey, the dark areas indicate regions 

where the surface roughness is less than the surrounding water. This could be caused by several 

phenomena including wind shadows, phytoplankton blooms or surface oil. In this case, the dark region 

leads from Holyhead Harbour towards the west; this is the route of several Irish Sea ferries and other

vessels. In the second figure, two parallel lines can be seen near the centre extending to the left of the 

figure which are likely to be ship’s tracks. It is possible that these dark zones are due to the loss of 

lubricants during normal vessel operation including through the stern tubes rather than spills or the 

pumping of bilge water which occur more intermittently. 
6 

Figure 1. ASAR images of a portion of the Irish Sea and Anglesey. The left hand image indicates the 

approximate ferry routing between Holyhead in Wales and Dublin in Ireland. The dark regions indicate 

zones with less surface roughness; this is caused by oil or lubricants on the surface lessening the surface 

roughness or, in the case of the area to the NW of the Lleyn Peninsular, wind shadow in the lee of 

mountains. The spread laterally is likely due to tidal excursion although several parallel tracks can be 

seen on the edges of the dark region. The right hand figure is a separate image of the region around the 

port of Holyhead and indicates how the bulk of the dark zone originates from the port of Holyhead and 

follows the route to Ireland. (Images from K. Gurion, M.Sc. Thesis, 2003). 

There are many different modes of action by which an oil or lubricant may adversely affect species and

these include: 

1. Direct toxicity of oil or lubricant components, especially to the liver and kidneys in mammals and 

fish, but also to the phytoplankton at the bottom of the food chain through reduction in 

photosynthesis. This may result in a reduction of food resources for higher trophic levels. 

2. Indirect toxicity by reducing the breeding success and by passage of compounds into the young 

or through suppression of the immune system. This may be through bioaccumulation or 

bioconcentration of compounds over a long period of time. 

3. Indirect effects induced through the increased Biochemical Oxygen Demand (BOD) from the 

organic matter. Bacteria may degrade the organic compounds and use oxygen at a faster rate in 

this process than it can be resupplied from the atmosphere leading to oxygen deficiency and 

anoxia. Animals require oxygen and will either need to migrate away from these zones or die. 

4. Smothering or irritation of gills, reducing their ability to pass oxygen across membranes. 

5. Removal of insulating properties, especially in marine mammals and birds. 
7 

The latter three effects might be common to both naturally derived and mineral oils, while the first two 

effects, essentially the most toxic effects, may be confined to mineral oils. Modes 1 and 2 are also 

relevant to lubricants discharged in operation, where the oil is emulsified within the water (and 

additives are more readily available for ingestion). Modes 3 to 5 are generally associated with gross oil 

contamination such as takes place with spills of crude oil cargoes or in regions of restricted water 

exchange. 

Lubricants consist of blends of base oils and additives, each with their own distinct chemical behaviour. 

It is, therefore, important to understand the chemical behaviour and environmental impact of all 

lubricant components (base oils and additives) released into the marine environment. The key aspects 

regarding the environmental impact of chemicals released into the sea can be broadly divided into three 

categories: 

• Biodegradation – the potential for a substance to break down in the environment due to biological 

action: is the chemical going to break down rapidly into harmless components in the sea? 

• Bioaccumulation – the tendency of a substance to permeate fatty tissue and enter the food chain: is 

the chemical going to accumulate in the fatty tissues of organisms and enter the food chain? 

• Toxicity – the ability of a substance to cause a harmful effect on an organism. 

All three aspects are directly related to the chemical structure of the molecules and so different 

formulations with different compositions will have different environmental effects in both the long and 

short term. 

This report reviews the environmental risk and fate of different types of base oils, which form the major 

part of the lubricant, on the basis of their biodegradability, toxicity and bioaccumulation potential.

Additives to the base oil are also addressed briefly. 

Base oil types 

When formulating a lubricant, it is necessary to take into consideration the intended application of the 

lubricant and the physical properties of the base oil such as its stability, the degree of corrosion 

protection offered, etc., all of which contribute to the effectiveness of the finished product. Some of 

these properties can be modified by treatment with additives, but the use of a base oil with good 

inherent properties results in a lower additive level and a more effective product. 

Conventional marine lubricants use a mineral oil base which is refined from crude oil. Occasionally 

synthetic hydrocarbon base oils are used, such as polyalphaolefins (PAOs) or polyglycols (PAGs), which

are again ultimately derived from crude oil. Alternatively, esters can be used as base oils and are 

frequently used for “biodegradable” lubricants. These may be naturally derived (e.g. rape seed, coconut 

oil, sunflower oil) or produced from petrochemical bases. All biologically sourced oils, whether animal or 

plants derived, are termed oleochemicals and this terminology will be used throughout. Practically, the 

majority of oleochemicals are from vegetable oils. 
8 

The base oils have been divided into groups by the American Petroleum Institute (API) according to their 

composition (see Appendix Two). The bulk (89.8%) of the base oils used are derived from the alkanes in

mineral oil although the exact chain length cut differs which will determine the viscosity. The synthetic 

oils derived from petroleum still only make up a small proportion of the total and the biologically based 

oleochemical base oils do not command a large share at present. The production routes for these oils 

are shown in Figure 2. The production routes also raise environmental concerns regarding the 

sustainability of source raw materials (Appendix Three), although this is not dealt with in detail in this 

review. 

Figure 2. Flow chart showing the production route for the Group V base oils. 
9 

2. Assessment Approach 

Published values for each of the toxicity, bioaccumulation and degradation rates are used where 

possible although data are not always available in the published scientific literature and remain within 

grey literature or the commercial sector. This review primarily considers the environmental properties

of lubricants based on the different types of base oil available. For the purposes of this review, base oil 

types are divided into their specific chemical groups, as follows: 

Petrochemicals 

1. Alkanes from partly refined crude oil. 

2. Alkanes from highly refined crude oil; these tend to have a narrower size range than the partly 

refined alkanes above. 

3. Polyalphaolefins (PAO) synthesised from highly refined components of crude oil. 

4. Polyalkylene Glygols (PAG) also synthesised from highly refined components of crude oil. 

5. Esters with component exclusively derived from highly refined crude oil components. 

Oleochemicals 

1. Esters synthesised with components derived principally from biological sources. 

2. Naturally occurring unmodified vegetable oils which are esters of fatty acids with glycerol. 

Degradation and biodegradation of these oil groups has been compared by considering their 

performance in standardised OECD (Organisation for Economic Co-operation and Development) tests. 

However, not all compounds have published results and comparative performance is used where 

necessary. Toxicity has been reviewed by considering the direct toxic effects of the chemicals on test

biota. These tests may be either acute or chronic in nature but are expressed in terms of the amount of 

chemical required to kill 50% of the test organisms. Bioaccumulation has been reviewed by reference to 

the water solubility and uptake into fatty tissue in model ecosystems or more usually through the 

octanol – water partition coefficient, an indirect measure of uptake. 

There are indirect toxic effects that may come into play in some areas, especially regions of restricted 

water exchange. The BOD associated with lubricant degradation may reduce the available oxygen in the 

water; this is of particular concern in harbours and ports which are sheltered and have less exchange 

with the oxygenated open sea water and also receive non-specific organic matter from urban runoff. 

This indirect toxicity is related to the degradability of the base oil rather than the direct chemical

toxicity. 
10 

Additives 

As well as the base oil, there are a range of additives in lubricants. Due to their diverse nature, it is 

beyond the scope of this report to cover these in any depth, however, a brief overview is presented 

since they form an important part of the product. 

Depending upon the intended use, between 1-30% of most lubricants are additives which enhance the 

performance of the product by increasing the contact between the metal surfaces and the lubricant, 

provide additional protection against corrosion and oil degradation, and improve operating performance

at extreme temperatures and pressures. These added compounds may include metals (e.g. zinc and 

molybdenum) or other organic compounds as antioxidants, rust inhibitors, viscosity modifiers, or 

surfactants. 
11 

3. Degradation and Biodegradation of Base Oils 

The major component of any lubricant is the base oil which may be obtained from a range of sources, 

including mineral and naturally-derived oils. The base oils may be a simple cut taken from the source 

material or may be synthesised from refined components; each composition will behave differently and 

have a range of environmental outcomes, depending on both physical (see Appendix Four) and chemical 

or biological processes. 

The chemical and biological degradation of oils are important processes which may ultimately control 

the environmental impacts of marine lubricant loss to the sea. These processes tend to start several 

days after introduction into the marine environment and may continue for many months or years 

afterwards, depending on the size of the discharge and chemicals involved (See Appendix Four). 

Ultimately the chemical composition of the base oil has an important role to play. The different 

formulations are discussed below. 

Alkanes in Lubricants 

The major components of base oils used in conventional mineral oil-based lubricants are alkanes in the

C15 to C50 range derived from crude oil. The base oils are not single compounds but groups of alkanes 

within specific size ranges where the shorter chain molecules are less viscous than the longer chain 

compounds. These straight chain alkanes (Figure 3) will degrade after the induction of a series of 

enzymes, according to the scheme shown in Appendix Four. Experiments with pure alkanes and crude 

oils (Binazadeh et al., 2009) showed that with an initial alkane loading of 150 g.l-1, 37% of the 

compounds were degraded in seven days. GC-MS analysis of the cultures of the bacteria Rhodococcus

had ketones, alcohols and aldehydes present, confirming the proposed degradation pathway. With 

crude oils and products including long chain waxes, there would be an apparent increase in the 

concentration of these longer chain compounds and the non-degradable components, as the shorter 

chain compounds are metabolised (see Figure 4). 

C15

C25

Figure 3. Alkanes of 15 and 25 carbons that may be present in base oils of this type. 

Some of the carbon present in the alkanes would become part of new microbial biomass while a smaller 

proportion may become more refractory with a slower degradation rate. These latter compounds, 

although not initially present in the base oil, may form part of the UCM (Figure 4) and persist beyond the 

28 days used in part of the OECD tests. 
12 

Experimentation has shown that the unsaturated compounds are most readily degraded followed by 

acids, straight chain alkanes, aromatics, and finally branched chain compounds. It is this differential 

degradability that leads to the characteristic hump of unresolved complex mixture (UCM) in the gas 

chromatograph (GC) profile of weathered oil which contains these branched materials. An example of 

weathering oil in the form of a GC trace can be seen in Figure 4. 

Figure 4. Change in gas chromatograph profile with weathering (from Philp and Kuder, 2008). In the 

initial figure, the alkane profile is readily apparent, peaking at a relatively short chain length of C12. After 

weathering, the short chain alkanes have been lost and there is a shift in the peak alkane in the sample 

to more waxy compounds (C28). After four months, a large Unresolved Complex Mixture (UCM, the 

hump) is apparent with few resolved alkanes visible. 
13 

Polyalphaoelfins (PAOs) in Lubricants 

PAOs are synthetic oils made from monomers such as 1-hexene (Figure 5) obtained from mineral oils. 

Figure 5. 1 -hexene, a typical monomer used in the manufacture of PAOs. Notice the absence of oxygen 

atoms in the molecule. The final product would be a polymer using several of these monomers joined 

together. 

The final base oils may be constructed of many monomers and have chain lengths up to 50 carbons long. 

It is possible to choose the chain length for a lubricant application, so high purity compounds tend to be 

the result for this base oil type. It is also likely that there will be side chains (branched structures) which 

have some of the longest degradation times of any group of hydrocarbons. 

Some industry studies (INEOS2) demonstrate that the shorter chain polymers with low viscosity degrade 

more quickly than the higher viscosity PAOs which may have longer chain lengths and more branching. 

Their results also indicated that degradation was slow within the first 21 days (<20%) and only achieved 

greater than 50% degradation after 40 days. There was also a stepwise change in the degradability, with 

only the two lowest viscosity products exhibiting greater than 50% degradation over the timescale of 

the test. Therefore, only the lowest viscosity products would pass the OECD degradability test although 

a considerable amount would still remain in the environment as 51% is still a pass. 

Polyalkylene (PAGs) and Polyethylene Glycols (PEGs) in Lubricants 

Polyalkylene glycols (PAGs) and polyethylene glycols (PEGs) are also synthesised from refined mineral oil 

components and fall into the petroleum sourced group of base oils. They may be synthesized to satisfy 

the application for which they are designed and may range from water soluble to water insoluble as 

required. Therefore, the environmental properties will depend on the chemical structure used (Figure 

6). 

Figure 6. Generic structure of a PAG. The carbon chain R may typically comprise of 10 – 20 carbons and 

the number of repeating units (n) may range from 4 – 7 in lubricant formulations. 

 

2

 http://www.ineosoligomers.com/media/files/pao/Durasyn%20Environmental%20Bulletin%202009.pdf 
14 

The water solubility and degradability of the PAGs and PEGs will be dependent to an extent on both the

number of carbon atoms, R, and the number of repeating sub-units, n. In general, the longer the carbon

chain, the lower the degradability. Long chain compounds with high molecular weight may also be nondegradable but may also be excluded from bioaccumulation as the molecules are too big to be taken up 

by biota (see below). 

Esters in Lubricants 

Naturally sourced vegetable oils 

The biologically sourced compounds used as replacements for crude oil-derived base oils may be based 

on esters with several different carbon chain lengths and structures. In some cases it is possible to used 

unmodified naturally-derived oils which are made from three fatty acids esterified to glycerol 

(triacylglycerol or triglycerides); this is the natural state of fatty acids in most vegetable seed oils. The 

generic structure can be seen in Figure 7 with three side chains of myristic acid (C14). 

O

O

O

O

O

O

Figure 7. Trimyristin, three C14 fatty acids joined to glycerol by ester linkages. This is the natural state for 

most fatty acids in seed oils. 

Vegetable oils and animal fats have different suites of fatty acids depending on the source; some are 

rich in short chain fatty acids (e.g. coconut oil) while others may be rich in unsaturated compounds (e.g. 

Canola oil). A summary of several common biologically sourced fats and oils can be seen in Table 3. 

Rapeseed oil (including Canola) is most frequently used in base oil formulations (LLINCWA, 2003). There 

are performance issues (e.g. oxidation and thermal stability) with vegetable oils related to the degree of 

unsaturation in the fatty acids and the overall stability of the lubricant. This would lead to the addition 

of more additives into the lubricant formulation to reduce the degree of oxidation and extend the 

operating temperatures. However, if in the sea, these triacylgycerols may be more readily assimilated by 

the marine biota (see Appendix Four). The presence of the carboxylic acid groups enables bacteria to 

more rapidly degrade the molecule.
Table 3 Fatty acid composition of several vegetable oils and animal fats which may be used as lubricant base oils. The Sat indication of the degree of total unsaturated fatty acids in the oil or fat (Mudge et al., 2008). 

Oil / Fat Sat / UnSat 10:0 12:0 14:0 16:0 18:0 18:1ω9 18:2ω6 18:3ωBeef Tallow 0.9 - - 3 24 19 43 3 1 Butterfat (cow) 0.5 3 3 11 27 12 29 2 1 Canola (rapeseed) Oil 15.7 - - - 4 2 62 22 10 

Cod Liver Oil 2.9 - - 8 17 - 22 5 - 

Coconut Oil 0.1 6 47 18 9 3 6 2 - Corn Oil 6.7 - - - 11 2 28 58 1 Cottonseed Oil 2.8 - - 1 22 3 19 54 1 Flaxseed Oil 9.0 - - - 3 7 21 16 53 Lard (Pork fat) 1.2 - - 2 26 14 44 10 - Olive Oil 4.6 - - - 13 3 71 10 1 Palm Oil 1.0 - - 1 45 4 40 10 - Palm Kernel Oil 0.2 4 48 16 8 3 15 2 - Peanut Oil 4.0 - - - 11 2 48 32 - Safflower Oil 10.1 - - - 7 2 13 78 - Sesame Oil 6.6 - - - 9 4 41 45 - Soybean Oil 5.7 - - - 11 4 24 54 7 Sunflower Oil 7.3 - - - 7 5 19 68 1 
16 

Synthetic esters 

Another synthesised ester used as a base oil is trimethyolpropane (TMP) with a mix of fatty acids (e.g.

octanoic and decanoic acids, Figure 8). Key aspects of these compounds are molecular weight, which can

be tuned by the choice of fatty acid, water solubility (tuned in the same manner) and lubricant 

performance. Other compounds may use mixtures with esters of longer chain fatty acids and TMP. 

These biologically-derived compounds may be liquids at room temperature due to the unsaturation of 

the alkyl chain and be significantly greater than 700 Daltons in molecular weight. 

Figure 8. One of the many biologically sourced ingredients to replace mineral oil components in the base 

oil. Note the similarity between this compound and the triacylglyceride shown in Figure 7. 

As with the natural triacylglycerides, there is a common degradation pathway for these compounds. 

Details can be found in Appendix Four but is essence, an enzyme will cut the side chains of the central 

part of the molecule and then remove two carbon subunits at a time. These carbons are then converted 

to either CO2 or biomass. One of the key features of these and related compounds is the presence of the 

carboxylic acid group (-COOH) which provides a “handle” for the metabolism of these compounds by 

biological enzyme systems. This group will also increase the water solubility of the molecule. In many

systems with esters of fatty acids such as triacylglycerol, lipase is needed to cleave the fatty acid from 

the rest of the molecule. Lipase is a water soluble enzyme present in most living organisms and is 

produced extra-cellularly in many cases. There is an induction period of a few days (Mudge & Pereira, 

1999) which then allows the free fatty acids to be incorporated into microbial biomass. 
17 

There are a range of compounds available which use fatty acid esters with different adjuncts such as 

adipic acid, trimethyolpropane (TMP) or glycol. These compounds will be rapidly degraded in the 

environment as the fatty acids provide the route for C2 removal (β – oxidation) as part of the acyl – CoA 

pathway. Essentially, anything that has an oxygen atom in the molecule will shorten the degradation 

time, increase water solubility and facilitate a more complete metabolism. The typical base compounds 

esterified with fatty acids can be seen in Figure 9. 

Adipic Acid

Trimethylolpropane

Glycol

Figure 9. Key base compounds used in esters with fatty acids to produce lubricant base oil. The presence 

of oxygen in the molecules allows polymers and esters to be formed. The presence of multiple alcohol 

groups provides the generic name of polyol for these compounds. 

One of the interesting by-products of enzyme induction in the presence of esterified fatty acids is cometabolism of compounds such as alkanes that usually take longer to degrade by themselves. 

Laboratory experiments and mesoscale box trials have shown that the introduction of fatty acid methyl 

esters to crude oil leads to a rapid degradation of the formerly slowly degraded compounds (Mudge & 

Pereira, 1999, Pereira & Mudge, 2004). This aspect has been exploited in an oil spill remediation case

(Mudge, unpublished results). 

Testing for Biodegradation of Marine Lubricants 

The OECD 306 "Biodegradability in seawater - closed bottle test" and the Marine BODIS test – ISO 

TC/147/SC5/WG4, N141, are specifically designed to test the biodegradation of organic substances in 

seawater. There are many other biodegradation test methods for freshwater and soil testing e.g. OECD 

301B Modified Sturm Test (freshwater), however, generically these are easier to pass then marine 

biodegradation tests due to the higher concentration of microorganisms being present in the inocula. 

Seawater typically contains 103 - 108 cfu.ml-1 (colony forming units) and river water typically 10

6

 - 107 

cfu.ml-1. Ideally, at least 108 cfu.ml-1 are required to get a consistent biodegradation result, assuming 
18 

the test sample contains organisms with the ability to biodegrade the test substance. This is one of the 

reasons why seawater biodegradation testing can be highly variable. 

Examining the different oils’ degradability using the OECD method 306, the base oils produced with 

either crude oil-derived or partly biologically derived (the fatty acid component) components, degrade

by these methods; however, these two groups will have different degradation rates in the first few days 

due to the larger number of enzymes needed to degrade the alkanes, but over a longer period, like the 

28 days of the OECD test, degredation will probably be similar. Measured data from commercial sources 

supports this view with similar measured degradation percentages for mineral oil and biologicallyderived base oil components. In the longer term, most of the alkanes of the oil may be degraded by this 

route, but the fatty acid esters with TMP may be partly degraded by one process and the remaining 

molecule will have higher water solubility and may enter other degradation pathways leading to 

complete removal. This can be seen schematically in Figure 10. 

Figure 10. Schematic degradation rates indicating a delay in the beginning for the alkanes due to 

enzyme induction and a smaller total degradation over 56 days due to the refractory nature of some 

longer chain components. 

The structure of the OECD tests for degradability have end points which will miss the differential 

behaviour between the base oils; the mineral oils comprised of alkane cuts require the induction of a 

series of enzymes by the in situ bacteria before the hydrocarbons are degraded. In contrast, the 

oleochemicals will have a much shorter lag phase as the enzyme systems are already in place for fatty 

acid degradation. This could lead to the situation where two different base oils have identical 

degradation values after 28 days although the initial rates were very different and the amount 

remaining at some stage in the future can also be different. 

In general, compounds that degrade quickly will have a smaller overall environmental impact than those

that persist for long periods of time. In this regard, the OECD test used to assess degradability has end 
19 

points at 28 and 56 days. It may be possible for a compound to pass this test in terms of the amount of 

chemical removed within the stipulated time, but if it then does not degrade further, it will have a 

greater overall environmental impact than one that continues to degrade. Improvements could be made 

to the tests to capture these differential effects between oils. 

Notwithstanding the different rates within the OECD tests, valid comparisons can be made between 

compounds at a fixed time or indeed at a range of times. A good summary figure has been produced by 

(Battersby, 2000) (Figure 11) which demonstrates the range of possible degradation rates and the 

advantage of some base oils, notably the vegetable oils, over other petroleum derived compounds. 

Figure 11. Summary figure showing the range of degradation rates (CEC L-33-A-93 test) for the different 

base oil types. From (Battersby, 2000). 

Base oils made from mineral oil and biologically-sourced hydrocarbons may nominally pass the OECD 

test and degrade to “acceptable levels” within 28 or 56 days, although of the different types, the fatty 

acid esters will degrade faster in the short term and have a smaller residual component. This 

degradability is good from one standpoint in that compounds will be converted to biomass or CO2 and 

“removed”, although in doing so, oxygen will be consumed. In the general respiration equation 

(Equation 1), the organic matter (represented by CH2O) is consumed in the presence of oxygen to 

produce carbon dioxide and water. This is typically called ultimate degradation in the OECD tests. 

 Equation 1. 

This degradability may introduce areas of concern, especially where the water exchange is slow, such as 

in some coastal areas with poor flushing. If significant amounts of degradable organic matter are 
20 

introduced, the bacteria may well remove the organic matter and the oxygen at the same time. This rate

might exceed the rate at which new oxygen is supplied across the atmosphere – water interface, 

especially if there is a film of oil present. This whole process may be compounded by readily degradable 

matter from fish processing and other industrial discharges, surface water runoff and combined sewer 

overflows entering the water mass as well. Poor water quality in terms of oxygen saturation may lower 

the diversity in the water mass. These oxygen depletion effects may be considered as indirect toxicity

effects due to degradability of the compounds rather than a direct chemical effect on an organism. 

Degradation & Biodegradation: Conclusions 

Table 4 shows that ester based oils have a much greater inherent degradation rate due to the presence 

of carboxylic acid groups that bacteria can readily utilise. These compounds will also be more water 

soluble than their equivalents without the presence of oxygen; this will also affect their bioaccumulation 

potential. Minerals oils with straight chain alkanes and branched polymers will degrade significantly 

more slowly, and to a less complete level, than the oleochemicals. The OECD tests do not capture the 

differential rates that exist between the compounds in the intervening time periods; the only reported

result is the percentage removed at 28 or 56 days but within that period, several different processes 

may have occurred. At present, a compound that passes the 50% threshold may be considered a pass 

but if 49% then remains and it does not degrade further, greater environmental impact will arise. 
21 

Table 4. Summary of differential biodegradation rates. 

Lubricant base 

oil 

Base oil source Market 

Share (%) 

Biodegradation 

Mineral oil Petroleum Persistent / 

Inherently 

Highly refined 

mineral oil 

Petroleum 

89.8 

Inherently 

Polyalphaolefin 

(PAO) 

Petroleum - 

synthesised 

hydrocarbon 

0.9 

Inherently / 

Readily 

Polyalkylene 

glycols (PAG) 

Petroleum - 

synthesised 

hydrocarbon 

Persistent 

Petroleum - 

synthesised 

hydrocarbon 

Readily 

Synthesised 

from biological 

sources 

Readily 

Ester 

Naturally 

occurring 

vegetable oils 

9.3 

Readily 
22 

4. Toxicity 

The chemical composition of the final lubricant products is a key factor in determining its direct toxicity, 

as is the manner in which it is used and the environment that receives the material. It is possible to

reduce the impact that a product has by altering these conditions. In the case of lubricants, the major 

factor will be the choice of chemicals used in the product formulation, as the environmental and usage

aspects will remain essentially constant between products. 

Mineral oil toxicity is dependent on the quality and fraction of oil used. Fractions with higher 

concentrations of aromatic constituents are more toxic than those without and within the alkanes, the 

shorter chain will be more available and, therefore, more toxic to biota. Tests frequently use the Water 

Accommodated Fraction (WAF) as only these components are available to affect the biota. Longer chain 

compounds are less water soluble and so less toxic in these cases. Polyglycols including PEGs and PAGs

are reported as being non-toxic (Stepina and Vesely, 1992). 

It is often stated that vegetable oils are benign and non-toxic in the environment. However this may not 

take into account the indirect effects of vegetable oil polymerisation. For example, after a spill of 

sunflower oil in the marine environment, the oil polymerised forming a stable material that bound the 

intertidal sediments together. The resulting mixture was stable for a considerable period of time 

(Mudge, 1997). Subsequent experiments indicated a variety of pathways for the degradation of this 

vegetable oil, and there was indirect toxicity associated with the formation of an impermeable cap over 

the sediments leading to oxygen deficits. This led to the death of many molluscs and invertebrates in the 

sediments (Pereira et al., 2003b). 

One of the key aspects regarding the toxicity was whether the oil went down the degradation or 

polymerisation route (Pereira et al., 2003a) which may be controlled by numerous factors including the 

quantity of oil in the environment and the degree of unsaturation of the fatty acids. Indirect toxic effects 

are possible due to the polymerised oil isolating the sediments from the atmosphere and causing the 

area underneath to become anoxic. The BOD associated with the degradation of the compounds can 

cause the same effect. 

Testing for Toxicity of Marine Lubricants 

When testing for toxicity, methods should be selected that represent the relevant trophic levels in the 

marine food chain. Typical test methods used are: 

• EN ISO 10253:1998 Water Quality – Marine Algal Growth Inhibition Test, 

• ISO 14669:1999(E) Water Quality – Determination of Acute Lethal Toxicity to Marine Copepods, 

• PARCOM method 1995 - Protocol for Fish Acute Toxicity test, 

• PARCOM 1995 - A sediment bioassay using an amphipod. 
23 

Using freshwater toxicity data may not may not accurately reflect the toxicity of a substance in the 

marine environment. The degree of correlation between freshwater and saltwater species is influenced 

by the three main factors (Wheeler et al., 2002): 

• biological differences between saltwater and freshwater organisms, 

• chemical differences in each medium, especially speciation and bioavailability, 

• methodological differences in tests that could lead to systematic differences in toxicity 

estimates. 

There is also a misconception that food grade additives are always safe to use in the marine 

environment. Many finished products that claim to be “food grade” are approved to the United States 

Department of Agriculture (USDA) H2 standard, which is for use in situations within food processing 

facilities where no food contact takes place – so toxicity is not of concern. Marine algae can be far more 

sensitive to a chemical than a human as their physiological mechanisms for dealing with toxins are very 

different. 

Toxicity - Conclusions 

In general, the oleochemical base oils have a low toxicity towards marine organisms (Table 5) with the

LC50 for fish toxicity reported as being ~10000 ppm for fatty acid esters and glycerol esters (LLINCWA, 

2003). Similarly, the polyol esters based on TMP and adipinic or oleic acid had LC50 of ~5500 ppm. As 

with many oily chemicals, the toxicity in some tests is not measureable as the LC50 exceeds the water 

solubility of the compound. In such cases, it is possible to induce physical effects such as smothering but 

this is not a chemical toxic effect. Some methodologies use the water-accommodated fraction, the part 

of the oil that will disperse or dissolve in water, although this is not a true reflection of the entire oil 

behaviour in the marine environment. 

In summary, the petroleum-based oils have a greater toxicity to biota in the marine food chain 

compared to the biologically sourced oils. This is related to the more rapid breakdown of the 

compounds once in the sea and ultimately affects the potential for bioaccumulation. This toxicity is 

independent of the degradation rate of the compounds (especially additives) and final products where 

there may be synergistic effects. Objective measures can be made between competing products with 

standard methods. 

The presence of additives is dependent on the choice of base oil and the intended function of the 

lubricant. However, several of the more toxic compounds in formulations are also the ones with poor 

degradability. The overall product toxicity may be significantly reduced by switching to a biologicallysourced base oil if used in conjunction with the use of low toxicity additives. 
24 

Table 5. Summary of comparative toxicity between base oils.

Lubricant base 

oil 

Base oil source Market 

Share (%) 

Toxicity 

Mineral oil Petroleum High 

Highly refined 

mineral oil 

Petroleum 89.8 Dependent 

on fraction 

Polyalphaolefin 

(PAO) 

Petroleum - 

synthesised 

hydrocarbon 

0.9 Low 

Polyalkylene 

glycols (PAG) 

Petroleum - 

synthesised 

hydrocarbon 

Low 

Petroleum - 

synthesised 

hydrocarbon 

Low 

Synthesised 

from biological 

sources 

Low 

Ester 

Naturally 

occurring 

vegetable oils 

9.3 

Low 
25 

5. Bioaccumulation 

The process of bioaccumulation is the build-up of chemicals within the tissues of an organism over time. 

Time is an important factor here as the longer the organism is exposed to the chemical and the longer 

the organism lives, the greater the accumulation of the chemical in the tissues. This may lead to higher 

exposures to that chemical over time. If the chemical has a slow degradation or depuration rate within

the organism (biological half life), concentrations within the tissues may eventually lead to adverse 

biological effects. It is, therefore, desirable to use compounds in formulations which do not 

bioaccumulate. It may not be possible to phase out all bioaccumulating compounds but it is feasible to

use chemicals which have a lower bioaccumulation potential, either through not being taken up as 

readily or by degrading more quickly both in the environment and in the organism. 

The bioaccumulation potential of a compound is directly related to its water solubility as chemicals that 

are not water soluble will tend to move into fatty tissues in preference to staying in water. These 

lipophilic chemicals include most of the compounds used in the manufacture of the base oil in 

lubricants. 

The water solubility of a compound is related to the type of atoms in the molecule and compounds 

comprised solely of carbon and hydrogen tend to have the lowest solubilities in water. This group 

includes the alkanes which form almost 90% of the current base oil in normal lubricant formulations. 

The inclusion of one or more oxygen atoms to a molecule will, in general, increase the water solubility 

and, therefore, lead to reduced bioaccumulation potentials. Compounds with oxygen also tend to be 

degraded more quickly in the environment or are excreted faster from organisms. 

In the context of naturally derived base oils used in lubricants, many of these are formulated around 

carboxylic acids and are both more water soluble and more readily degraded. Therefore, the 

bioaccumulation potential is reduced in comparison to alkane-based oils. The polyalphaolefins (PAOs) 

are also exclusively comprised of carbon and hydrogen and usually synthesised from mineral oil; one of

the common alphaolefins is 1-hexene and can be seen in Figure 5. The water solubilities of a series of six 

carbon compounds can be seen in Table 6. This illustrates how the molecular configuration and 

presence of oxygen affects the water solubility. It would be expected that the bioaccumulation potential 

will be greatest with the least soluble compound. 
26 

Table 6. The solubility of six carbon compounds in relation to the number of oxygen atoms in the 

molecule. The octanol – water partition coefficient (KOW) is often used as a proxy for bioaccumulation 

potential. 

Compound 

Number of oxygen 

atoms 

Water Solubility 

(mg.L-1) 

Log KOW

Hexane 0 10 3.90 

Hexene 0 50 3.39 

Hexanal 1 5640 1.78 

Hexan-1-ol 1 5900 2.03 

Hexanoic acid 2 11000 1.92 

Hexan-2-one 1 14000 1.38 

Values from www.chemspider.com

In comparative studies between the bioaccumulation of mineral oil and PAOs into a bottom dwelling fish

species (Rushing et al., 1991) the PAOs did not accumulate in the tissue at all while the mineral oil was 

found in all samples. In this study of drilling muds, effects could be seen 12 km from the initial source for 

the mineral oils and they related this to the overall adverse effects on the biota. 

It has been assumed for some time that larger molecules are not bioaccumulated as they are unable to 

physically pass through the membranes of cells and be incorporated into the living cells (Arnot et al., 

2010). Therefore, when designing lubricant formulations, the molecular size of the components of the 

base oil have been considered as they will directly affect the rate of uptake. However, there have been 

several criteria proposed over the past few years to describe the point at which chemicals are no longer 

taken up in the body and bioaccumulated (Arnot et al., 2010). The major physical properties that have 

been used previously are the maximum molecular diameter or the effective molecular diameter, the 

octanol – water partition coefficient (KOW) or water solubility and the molecular mass. 

In an evaluation of data for esters, there was a strong link between the log KOW and the log 

Bioconcentration Factor (BCF) while the other factors had less well-defined relationships. The selection 

criteria chosen by the Canadian Government and United Nations Environment Programme (UNEP) 

(Canada, 2000; UNEP, 2001) and the United States Environmental Protection Agency (USEPA, 1999) led 

to cut-off log KOW values of ~5. Of the 300 chemicals studied, only 12 appear to be greater than the 

European Union’s preferred value of 700 Daltons. What is clear from this review is that there is no single 

criterion to adequately describe the BCF and a holistic approach integrating several factors including

measured uptake and elimination rates has been proposed by Arnot et al. (2010). 
27 

Testing for Bioaccumulation of Marine Lubricants 

The two most common test methods for establishing bioaccumulation potential are OECD 117 and 107. 

The test substance is added to a mixture of octanol and water and its dissolution in each phase detected 

using generally gas chromatography or an infra red detector. The bioaccumulation of the substance is 

measured by establishing its partition coefficient (expressed as log Kow) in octanol and water. The 

octanol mimics the fatty tissue in an organism and the water, the seawater. Substances that have a 

tendency to bioaccumulate will preferentially dissolve in the octanol rather than the water. Therefore, 

the greater the log Kow, the greater the likelihood that the substance will bioaccumulate. 

Partition coefficients for the marine environment are normally measured on a log scale between 0-6. 

Substances with log Kow <3 are deemed not to bioaccumulate and those with log Kow >3 are deemed to 

be bioaccumulating. 

Seawater may increase the likelihood of uptake by organisms in comparison to freshwater due to 

“salting out” of lipophilic substances. Therefore, although freshwater is used in these test methods, as 

long as conservative acceptance limits are set then they can be used as an indicator of bioaccumulation 

potential in the marine environment. The use of these test methods as an indicator of a substance’s 

bioaccumulation potential can negate the need to carry out in vivo or in vitro fish or mussel testing. 

Bioaccumulation - Conclusions 

In summary, the level to which a component of the product is bioaccumulated in an organism or 

biomagnified up the food chain will be dependent on the environmental and biological half-lives of the

compounds (some will degrade before being incorporated into an organism and some will be 

metabolised within the organism) as well as the lipophilic nature of the compounds (as measured by 

water solubility). Any component that has low water solubility will potentially bioaccumulate in an 

organism and in this case, fatty acid-containing components will have an advantage due to greater 

water solubility and faster short term degradation. Therefore, there is a distinct advantage in using 

esters over the other carbon and hydrogen alone base oil types (Table 7). 
28 

Table 7. Summary of bioaccumulation potential of the different base oil types. 

Lubricant base 

oil 

Base oil source Market 

Share (%) 

Potential for 

Bioaccumulation 

Mineral oil Petroleum Yes 

Highly refined 

mineral oil 

Petroleum 89.8 

Yes 

Polyalphaolefin 

(PAO) 

Petroleum - 

synthesised 

hydrocarbon 

0.9 Yes 

Polyalkylene 

glycols (PAG) 

Petroleum - 

synthesised 

hydrocarbon 

No 

Petroleum - 

synthesised 

hydrocarbon 

No 

Synthesised 

from biological 

sources 

No 

Ester 

Naturally 

occurring 

vegetable oils 

9.3 

No 
29 

6. Additives in Marine Lubricants 

Although this report reviews the fate of the base oil components of marine lubricants, it is important to 

consider these ingredients as the different base oils demand different suites of additives in the final 

product formulation. Additives have many functions and may be necessary for the product to work as 

described; the quality of the base oil directly affects the composition of the additive package used. Some 

compounds provide corrosion inhibition, for example, while others prevent the oxidation of the major 

base oil components or impart other desirable properties of the lubricant. 

The greatest proportion of additives are found in engine oil formulations which contain large amounts of 

detergents which also act as an alkali reserve to neutralise acidic combustion products e.g. sulphonates, 

phenates and salicylates. Dispersants, anti-wears, anti-oxidants and corrosion inhibitors are also added. 

These formulations may also be used in other applications and most notably engine oils are commonly 

used as stern tube lubricants. These lubricants readily emulsify with water, which may affect their 

toxicity, with the additive component readily available to marine life. 

Among this group of chemicals are surfactants which may be present at the 5 – 25% level. Since this 

class of compounds may well be manufactured or sourced from biological materials, these could be 

considered environmentally sustainable themselves. Indeed, some clothes detergents and liquid laundry 

products market themselves on this basis by sourcing the alkyl part of the surface active agent from 

vegetable oils. These compounds will have appreciable water solubility by definition and can frequently 

be degraded rapidly in the environment. Polyethoxylates are less likely to have a biological source 

compared to alkyl sulphates although the first biologically sourced ethoxylate was announced in the first 

quarter of 2010. 

Many trace additives (<1%) are relatively small (<700 Daltons) and have measureable toxicity toward 

lower level food chain organisms but not towards fish. Despite being present at low concentrations in

the lubricant, the additives used in some formulations may continue to have a deleterious effects on the 

basis of a combination of their high water solubility (Kow >4 in most cases), low molecular weight, and 

slow degradability as measured by the OECD methods.

The chemical composition of these compounds indicates that there may be biologically-derived 

alternatives (e.g. succinic acid with a single fatty acid as an ester) although there would need to be some 

fine-tuning of the chain length in order to satisfy performance requirements as well as providing 

desirable Kow and degradability characteristics. 
30 

7. General Conclusions 

The majority of lubricants produce a sheen when on water, although some products with high 

concentrations of detergents are more likely to emulsify and not produce a sheen. This is not surprising 

as the base oil, whether from natural or oil based sources, will still produce sheen, unless the viscosity is 

too great to facilitate spreading. The presence of sheen on the water indicates a leakage or spill has

occurred. Therefore, there are benefits to having sheen to assist in noticing a loss, but in the case of the 

loss of lubricants from the stern tube, emulsification of the lubricant at the propeller prevents excessive 

lubricant forming sheen under seal failure conditions, with the result that larger amounts of oil can be 

released without external detection. There is some evidence of routine loss of lubricants in shipping 

lanes that leave materials on the surface capable of being detected by satellites. 

A summary of major factors, biodegradation, toxicity and bioaccumulation potential, for each of the 

base oil types can be seen in Table 8. In this table, the three major criteria are presented for each base 

oil and colour coded to indicate the environmental outcome. Those base oils that degrade quickly are 

considered better than those that do not rapidly degrade, although there is a trade-off with regard to

the depletion of oxygen during compound metabolism. Those compounds that do not bioaccumulate 

and are relatively less toxic are considered better than those that bioaccumulate and have higher 

toxicities. 

From this table it can be seen that currently the majority of the base oils are of the type with the 

smallest biodegradation rate, a high potential for bioaccumulation and have a measureable toxicity 

towards marine organisms. In contrast, the base oils derived from oleochemicals degrade faster and 

have a smaller residual, do not bioaccumulate appreciably and have a lower toxicity to marine 

organisms. On the basis of this simple comparison, lower environmental impacts will arise if a greater

proportion of base oils were manufactured from biologically sourced materials. 
31 

Table 8. Comparative environmental behaviour of lubricants based on the base oil type. The 

biodegradation rate refers to aerobic degradation measured by OECD 301B (LLINCWA, 2003); the 

anaerobic rates are ca. 5x less than the aerobic rates. 

Lubricant base 

oil 

Base oil source Market 

Share (%) 

Biodegradation Potential for 

Bioaccumulation 

Toxicity 

Mineral oil Petroleum Persistent / 

Inherently 

Yes High 

Highly refined 

mineral oil 

Petroleum 

89.8 

Inherently Yes 

Dependent 

on fraction 

Polyalphaolefin 

(PAO) 

Petroleum - 

synthesised 

hydrocarbon 

0.9 

Inherently / 

Readily 

Yes Low 

Polyalkylene 

glycols (PAG) 

Petroleum - 

synthesised 

hydrocarbon 

Persistent No Low 

Petroleum - 

synthesised 

hydrocarbon 

Readily No Low 

Synthesised 

from biological 

sources 

Readily No Low 

Ester 

Naturally 

occurring 

vegetable oils 

9.3 

Readily No Low 

While lubricants can and have been made from crude oil-derived base stocks for many years, there are 

viable alternatives with biologically-sourced components that have a reduced environmental impact. 

Even within the biologically sourced or partially biologically-sourced components, there are differences 

in overall environmental fate. While there is not a big difference in degradability between some oil 

based materials and biologically-sourced base oils over the 28 days of the OECD degradation methods, 

there are measurable improvements when it comes to 56 days and when considering the molecular size 

and water solubility, and ultimate environmental impact. The current OECD tests are useful but with end 

points of just 28 and 56 days, improvements are required to establish the longer term effects. 
32 

Base chemicals comprising alkanes currently have the largest share of the market and yet also have the

slowest degradation rates, greatest potential for bioaccumulation and toxicity. More refined products 

and synthesised hydrocarbons such as PAOs and PAGs have a better environmental performance but 

those entirely derived from oleochemicals perform best in these regards. The opportunity now exists for 

a shift in base oil composition as products with better environmental credentials fulfil all the roles that 

lubricants are currently used for. 

It is widely accepted that all forms of base oil derived from mineral oil degrade more slowly in the 

environment and with a smaller ultimate conversion to carbon dioxide and water than base oils from 

vegetable sources. The more refined compounds have faster degradation rates than simple alkane cuts 

from crude oil but those base oils derived from biological sources are still ultimately better in the long 

term. One caveat may be the rapid loss of readily degradable compounds leading to reduced 

oxygenation in regions of restricted exchange. The role of lubricants in this process has yet to be 

established, as frequently ports and harbours, an example of a region of restricted exchange, also 

receive municipal wastes which confound the issue. 

In the open sea, the routine loss of lubricants as part of normal operations can be seen in the satellite 

images (Figure 1) though quantifying the magnitude of individual routes will require near real time 

satellite images to guide sampling transects. Surface waters could be collected and gas chromatographic 

analysis would be able to identify and quantify the losses. This could form an important research project 

that demonstrates the current situation and delimits the surface water concentrations of the different

base oil types. A similar study could be undertaken in ports and harbours with restricted exchange 

where surface water concentrations may build up over time. 

All the mineral oil components are generally more toxic than the biologically sourced base oils and 

although it may be argued that concentrations of these components are globally small from this source,

there are additive effects from other oils released or lost and the potential for sub-lethal eco-toxic

effects. Long term mesocosm studies of the low level inputs may shed light on these deleterious effects, 

if present. Linked to toxicity, is the potential for bioaccumulation which is related to the chemical 

structure, water solubility, degradation and depuration rates. Although there are some questions about

the exact cut off between chemicals that can bioaccumulate and those that cannot, the move to larger 

molecules such as biologically sourced esters would alleviate any issues that arise. 

What may be harder to achieve is the selection of environmentally responsible additives, comprising 

surfactants, corrosion inhibitors, anti-oxidants etc. Although these components only make up a few 

percent of the final formulation, these are the ones that have the slower degradation rates (<20% in the 

OECD tests and classed as persistent) and may be more toxic (comparatively). They can also affect the 

overall environmental performance of the lubricant i.e. a low concentration of a highly toxic additive can

result in the final formulation having a high toxicity. In some cases, the chemical structures lend 

themselves to substitution with biologically-derived components, although these may need to be tuned 

to ensure that the right performance properties are maintained. As with base oils however, it is 

important to select additives with good environmental performance i.e. high biodegradability, low 

toxicity and low bioaccumulation potential. However, selecting a base oil with good technical 
33 

performance should reduce the total additive load needed in the product formulation resulting in a win

– win situation. 

Base oils and additives used in marine applications should be selected for their environmental 

performance in the marine environment and test methods employed should reflect this. This however 

should not be to the detriment of their technical performance, as any environmentally responsible 

lubricant should have at least the same technical performance as a conventional product. This will help 

ensure that equipment functions efficiently, minimising failure. An environmentally responsible 

lubricant with good technical performance will minimise the potential for any leaks, however, in the 

event of an incident will minimise the environmental impact of any lubricant leaked into the sea.
34 

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biodegradable water-cooling two-stroke engine oil. In Proceedings of the 2006 Spring Technical 

Conference of the ASME Internal Combustion Engine Division, pp. 693-699. New York: Amer Soc 

Mechanical Engineers. 

UNEP. 2001. Final Act of the Conference of Plenipotentiaries on the Stockholm Convention on Persistent

Organic Pollutants. . G. (CH), United Nations Environment Program. 

USEPA. 1999. Category for Persistent, Bioaccumulative, and Toxic New Chemical Substances. Fed Reg 64: 

60194-60204. 

Wang, Z.D. & Brown, C., 2008. Chemical Fingerprinting of Petroleum Hydrocarbons. In Methods in 

Environmental Forensics, (ed. S.M. Mudge): Taylor and Francis. 

Wheeler, J.R., Leung, K.M.Y., Morritt, D., Sorokin, N., Rogers, H., Toy, R., Holt, M., Whitehouse, P., Crane, 

M. , 2002. Freshwater to Saltwater Toxicity Extrapolation Using Species Sensitivity Distributions. 

Environmental Toxicology and Chemistry, 21(11), 2459–2467. 
36 

APPENDIX ONE. Lubricant pathways from shipping to the Marine Environment

Lubricants from shipping make their way into the marine environment in a number of ways. Cranes, 

winches, windlasses and other types of equipment on the decks of ships are all lubricated by oils and 

greases, or use hydraulic fluids to transmit power. These are nominally sealed systems but leaks may 

occur, or components such as hydraulic hoses fail, resulting in spills of oil onto the deck. During 

maintenance activities and equipment repairs, oil systems may be drained, refilled or levels topped up. 

Many small spills occur when handling oils during these operations. All of this oil will make its way into 

the scuppers and over the side of the vessel, forming a visible oil layer on the water surface. 

There are also many items of the vessel’s equipment which are located below the waterline and have a 

shaft or component projecting outside the vessel’s hull. The main examples are the stern tube where 

the propeller shaft passes through the hull, the rudder shaft bearing, tunnel or azimuth thrusters used 

for manoeuvring or propulsion, and horizontal stabilizers on passenger ships. In these systems, the 

lubricant is maintained at a higher pressure than the water outside (to prevent ingress) and is separated 

by an elastomer seal. Normal operation sees a gradual discharge across barrier seals into the sea. 

Lubricants used in these systems generally form emulsions with water, to prevent free water affecting 

equipment reliability in the event of water ingress to the lubrication system. A consequence is that the 

lubricant disperses or settles to the bottom when leakage occurs and no oil film is evident on the water 

surface. This discharge takes place, to a greater or lesser degree, all the time that the vessel is afloat. It 

is not obvious, unlike a spill from the deck and is, therefore, often overlooked. 

Within the machinery spaces of a vessel are the engines and ancillary equipment such as air 

compressors, hydraulic systems, pumps, etc. These are in a sealed environment so spills and leaks 

should not be able to make their way into the sea. Engines contribute to discharges into the 

environment in another way, however. Four-stroke engines use a sealed lubricant system where the 

lubricant is re-circulated and has a long service life. Consumption and top-up between planned oil 

replacements is minimal. Many large marine engines operate on the two-stroke principle. Two-stroke 

engines use oil as a lubricant but instead of it being part of a closed crank case system, the lubricant is 

directly injected into the engine cylinder to lubricate and seal the piston. There is evidence (Tang et al., 

2006) that a substantial amount of this oil remains unused within the engine (30 - 50%) and exits with

the combustion gases and enters the marine environment by this route. This is also true of small 

outboard motors, although this constitutes a small loss compared to the larger fixed engine installations. 

The losses from outboards also tend to be close to shore such as in harbours and other sheltered water. 

Lubricants from equipment located within the machinery spaces should not normally be able to make its 

way into the sea since in the event of a spill or leak it goes into the vessel’s bilge, where interceptors 

capture the oil and separate it from bilge water which is discharged overboard. A large volume spill or 

equipment malfunction, however, could potentially overwhelm an oil interceptor resulting in a spill. 
37 

APPENDIX TWO. American Petroleum Institute (API) grouping of lubricants 

Table A1. The five major base oil groups according to the API together with their market share. Groups I, 

II and III are cuts of refined mineral oil and group IV is synthesised from mineral oil precursors. Only 

group V contains non-petroleum based oils along with other non-alkane petroleum components. The 

market share is for 2007. 

Group Base Oil Source Chemical Composition Usages Market Share 

(%) 

I 

Light end alkanes with a 

minimum of 10% 

aromatic content 

Cylinder oils 

System oils 

Trunk piston engine oils 

Marine diesel oils 

Multigrades 

Hydraulic oils 

Mineral gear oils 

Turbine & heat transfer oils 

Refrigeration Oils 

Greases

64.4 

II 

Light end alkanes with a 

maximum of 10% 

aromatic content 

Multigrades 

Hydraulic oils 

Turbine & heat transfer oils

20.0 

III 

Petroleum 

base, from 

distillation 

Mid-range alkanes 

Multigrades 

Hydraulic oils 

Turbine & heat transfer oils

5.4 

IV 

Petroleum 

base, from 

synthesis 

PAO 

Multigrades 

Synthetic gear oils 

Synthetic compressor oils

0.9 

V 

Derived from 

either mineral 

oil (distillation) 

or synthesised 

from mineral 

and/or 

vegetable 

sources 

All other oils including 

naphthenics and esters 

Hydraulic oils 

Synthetic gear oils 

Synthetic compressor oils 

Turbine & heat transfer oils 

Refrigeration oils 

Greases

9.3 
38 

APPENDIX THREE: Sustainability Of Sources 

Renewability of the components in lubricant formulations, especially the base oil, has an indirect 

environmental impact. Sourcing of renewable base stocks from verified sources can minimise the 

overall environmental impact of the lubricant. There is a perception that incorporation of biologically 

derived materials into products has a lower CO2 charge and does not deplete scarce resources like crude 

oil. There is some debate as to the benefit of using vegetable oils instead of mineral oils, depending on 

how they are produced (Mudge, 2008). Full life-cycle analysis of individual sources and processes may 

be appropriate in the medium term to assess the overall sustainability of using vegetable sources. 

However, there are benefits from using renewable materials rather than non-renewable crude oil in the 

long term. 

Crude oil-derived ingredients are not renewable except on geological timescales and cause 

environmental damage during the prospecting, extraction, transportation, storage and refining phases. 

In contrast, biologically-derived materials are renewable on human timescales, are carbon neutral or 

have a small carbon footprint, but may also cause environmental issues with the extraction, 

transportation, storage and refining phases - as with crude oil. It has been argued in the past by some 

vegetable oil producers that their products are less damaging than crude oil and they had sought an 

exemption under the US Oil Pollution Act (1990), but this was denied by the US Environmental 

Protection Agency based on the behaviour of vegetable oil spills in the marine environment (Mudge, 

1995). 
39 

APPENDIX FOUR. Physical Processes for the Biodegradation of Oils in the Marine 

Environment 

Once in the marine environment, all oils may undergo a range of chemical and physical transformations 

which lead to a reduction in the total hydrocarbons with time. These processes are generic to all oil 

hydrocarbons, including those from natural sources. Some of these processes are physical, while others 

involve the indigenous biota (see below). A summary of these processes may be seen in Figure A1. 

Figure A1. A schematic diagram showing the processes that oil on water might undergo. 

The magnitude of each process is dependent on the type of oil spilled. For instance, light mineral oils 

and refined fuels will undergo substantially more evaporation, spreading and solubilisation than heavy

crudes, vegetable oils and bunker fuel oils. For marine lubricants, the formulations have different 

properties and the two major release scenarios (onto the surface of the water or sub-surface) will lead 

to a range of rates for each process. A schematic diagram summarising the timescales for the major 

processes can be seen in Figure A2. Subsurface losses through stern tubes, for example, will emulsify 

quickly and tend to settle out of the water column and reach the benthos. Therefore, the surface related 

processes will not occur and the sub-surface ones will dominate (sedimentation and biodegradation). 
40 

Figure A2. The timescales for the processes acting on spilled oil. After one week, only the sedimentation 

and biodegradation processes remain important. (From ITOPF3) 

In any surface spill, the oil or lubricant will spread across the surface of the water; the rate at which this 

happens is dependent on the viscosity and volume of the spilled oil and the environmental temperature.

Water temperature greatly affects the viscosity of the oil and determine the area which it will cover and 

the film thickness. The global seawater temperature may vary from ~-2°C in polar regions to ~32°C in 

tropical sheltered locations. In most European waters, the temperature extremes are ~5°C – 25°C 

(Nygard & Dring, 2008). At low temperatures, oils and lubricants will be considerably more viscous than 

at warmer temperatures and will spread much more slowly. 

The compounds on the surface of the water may be exposed to the air and sunlight. Some of the 

hydrocarbons in the oil may react with oxygen in the presence of sunlight to form either water soluble

products or tars which may persist longer than the original compounds4. In most crude oil spills, this is 

not an important process but it may have a greater significance with refined oil products such as 

lubricants. 

The rate of evaporation will also be greatly dependent on the chemical composition of the oil or oilderived product as the light short chain hydrocarbons will evaporate considerably more quickly than the 

longer chain, more waxy components. The rate of loss of compounds to the atmosphere will also 

depend on the film thickness and, therefore, the spreading of the oil. As these short chain compounds 

evaporate, the remaining oil becomes thicker (more viscous) and heavier. This may lead to some of the 

oil sinking out of the surface zone to the benthos, where it may accumulate in the sediments. Lubricant 

base oils are normally of a limited range of hydrocarbon chain lengths and are not volatile. Evaporation 

is not likely to be a significant factor when considering spills of most lubricants. 

As the oil sinks through the water column, the more water soluble components may dissolve into the 

water. These components tend to be the smaller ones (lower molecular weight) and include some of the 

 

3

 ITOPF – The International Tanker Owners Pollution Federation Limited (http://www.itopf.com) 

4

 http://www.itopf.com/marine-spills/fate/ 
41 

additives. In some cases, the water soluble fraction is the part of the oil or lubricant that has the highest 

toxicity associated with it, as these compounds may be readily taken up by organisms (Pollino & 

Holdway, 2002). 
42 

APPENDIX FOUR. CHEMICAL AND BIOLOGICAL PROCESSES OF THE DEGRADATION AND 

BIODEGRADATION OF OILS IN THE MARINE ENVIRONMENT 

Degradation may occur through pure chemical processes, e.g. oxidation, but the most active processes 

are performed by micro-organisms in the water column or in the sediment. Seawater naturally contains 

a wide range of bacteria which are able to metabolise oil and the compounds within oil as a carbon 

source (energy supply). However, oil hydrocarbons are not the most readily available carbon source and

require a series of enzymes to be induced before the process can begin. This accounts for the delay in

the start of biodegradation. Examples of one biodegradation pathway (among many) that may occur on 

alkanes can be seen in Figure A3 and on aromatics in Figure A4. 

1

2

3

4

alkane (octane)

aldehyde (octanal)

acid (octanoic acid)

octanoyl - CoA

alcohol (octanol)

1

2

3

4

alkane (octane)

aldehyde (octanal)

acid (octanoic acid)

octanoyl - CoA

alcohol (octanol)

Figure A3. A schematic degradation pathway for an alkane. Steps 1 – 4 are catalysed by the following 

enzymes, respectively: 1. alkane monooxygenase; 2. alcohol dehydrogenase; 3. aldehyde 

dehydrogenase; 4. acyl-CoA synthetase (Ishige et al., 2003). 

Figure A4. Part of the pathway for the aqueous degradation of aromatic ring structures. The resulting 

compounds have greater water solubilities than the parent compounds. Polyaromatic compounds with 

more than four rings are generally considered to be refractory and do not degrade by these mechanisms 

(Mudge & Seguel, 1997). 
43 

The short chain alkanes typically used in lubricant base oils would be lost through biodegradation within 

one month as shown here, although some of this loss may not be to biomass and CO2 but to 

intermediate compounds which may be more refractile. These would contribute to the UCM and result 

in incomplete degradation over the 56 days test period of the OECD methods. Some ring structures and 

large complex chemicals are very resistant to degradation and these compounds may persist for many 

years. A good example of such a group is the steranes and terpanes present in crude oil and frequently

used as biomarkers to identify the source of the original crude oil spillage (Wang & Brown, 2008). These 

chemicals generally resist weathering and persist in the environment for many years. 

The fatty acids present in some base oils will undergo a series of degradation steps, depending upon the 

chemical structure. In the case of most esters, the first stage would be the induction of a lipase enzyme 

to cleave the fatty acid from the rest of the molecule. Once free, the fatty acid would undergo chain 

shortening through β-oxidation, another enzymatic process. The net result of this process is the removal 

of two carbon subunits from the fatty acid sequentially until the fatty acid has been fully utilised (Figure 

A5). The fatty acids would gradually become smaller and, therefore, more soluble as the influence of the 

alkyl chain diminishes. 

+ 2 CH2

β-oxidation process

OH

O

OH

O

+ 2 CH2

β-oxidation process

OH

O

OH

O

Figure A5. A summary of the β-oxidation process acting upon the closest two carbons to the carboxylic 

acid group. The resulting smaller compounds are, in general, more water soluble than the parent 

compounds.