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 .........................................

................................................... ................................................ 342



## Summary Lubricants are used to reduce the friction between surfaces, reduce corrosion and isolate metal surfac es from water. They are extremely important for the sa fe and effective operation of most machines, including those found on board ships. The use of l ubricants on board ship often results in the lubric ant entering the sea through wash off, discharge, spill s or leaks. These small, but frequent inputs resul t in a significant amount of chemicals entering the sea on an annual basis (estimated 38-62 million litres pe r year). The lack of legislation controlling these i nputs and the nature of these chemicals can result in potentially persistent, bioaccumulative and toxic c hemicals 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 u ndergo in the marine environment and use this to select components with the lowest possible environm ental impact.
According to the American Petroleum Institute (API) , the base oils, the major component of lubricants, can be made from petroleum or oleochemical (biologi cal) 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 petrochem ical industries. Biologically sourced oils tend to be from vegetable seed crops in the form of esters.
The biodegradability of the base oils depends on th e chemical formulation with many of the mineral oil components including alkanes having the slowest rat es 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 sufficien t to differentiate between some oils as the initial r ate and proportion that is ultimately degraded may be missed. Naturally occurring marine organisms are ab le 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 pr esence of oxygen in the constituent molecules which also increases the water solubility of these chemic als.
Chemicals are taken up by organisms (bioaccumulated ) in the marine environment with those compounds that are least water soluble being more r eadily accumulated. The process is called bioaccumulation and will depend upon the environmen tal and biological half life of the compounds; those chemicals that degrade quickly will not bioac cumulate 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 bioaccumulatio n potential.
Some chemicals are inherently toxic and the base oi l components will exhibit a degree of toxicity towards marine organisms. The magnitude of this tox icity is also dependent on the fraction or cut of mineral oil used in the lubricant products. Those c ontaining aromatic hydrocarbons such as unrefined o r partly refined crude oil will have an inherently hi gher toxicity. In general, however, all crude oil d erived fractions have the higher toxicity than those deriv ed from oleochemicals.
The nature and quality of the base oil will also de termine which compounds need to be present in addition to the base oil to ensure a suitable perfo rmance during use. These additives may only be3

present in small amounts but may be toxic. Minimisi ng 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 miner al oil derived base oils have the greatest environment al effects; they also currently have the largest share of the marine lubricant market. In contrast, the o leochemical 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 shi ft in the choice of base oil from petroleum derived to oleochemicals.
Irrespective of whether a base oil is mineral oil o r oleochemical based, its environmental characteris tics should be assessed to ensure base oils with the bes t environmental performance are selected. This is equally true for the additives used in lubricant fo rmulations. A small concentration of highly toxic additive may completely change the toxicity of the final lubricant. It is therefore important to asse ss 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 u sed to ensure representative testing is carried
out.4



## 1. Introduction to Marine Lubricants Concerns about the environmental impacts of lubrica nts used at sea are growing but as yet there is no international legislation in place to monitor or co ntrol operational discharges of lubricants in the o pen ocean. The International Maritime Organization (IMO ) recommends lubricants with high biodegradability for Arctic seas, while under the O SPAR Convention for the North East Atlantic offshor e industry, including oil and gas platforms, lubrican ts must meet environmental standards under the HMCS (Harmonised Mandatory Control Scheme) programm e. There are no such standards for the shipping industry and, in general, no discharges ar e recorded unless a prosecution for a large scale spillage is made.
According to industry figures, the total global mar ket for marine lubricants is around 2.8 x 10 9 litres per year and this can be broken down into the various s ectors as shown in Table 1.

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

Lubricant Usage Volume (x10 3 litres) Cylinder Oils 1,500,000 System Oils 1 400,000 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 th e total) with dedicated stern tube oils only used w hen leaks are occurring from the seals.
Etkin (2009) reported that between 38 – 62 x 10 6 litres of lubricant are lost to the environment 1 each year with a significant proportion occurring in por ts and harbours; the remaining losses occur while t he vessels are underway and the lubricants are lost to the open ocean and coastal seas where they are les s

1 See Appendix One: Lubricant pathways from shipping to the Marine Environment5

visible. The environmental impact will usually be l ess 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 wide ly dispersed which aids in the degradation process.

The difference between the total market for lubrica nts (2.85 x 10 9 litres, see Table 1) and the environmental losses (~1.2 x 10 8 litres, (Etkin, 2009)) suggests that 2.7 x 10 9 litres (95%) are “consumed” annually, with a proportion being recycled or reuse d as something else ( **e.g.** fuel) with the rest being converted to a product ( **e.g** . CO 2 ) by processes such as combustion. In a wide rangin g review of oil entering the marine environment, the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) indicated that so me small two stroke engines **e.g.** those used on small fishing and leisure vessels, may emit up to 2 5% of the fuel – lubricating oil mixture while runn ing (GESAMP, 2007). Combustion will produce unburned hy drocarbons, partially oxidised products and soot which enter the marine environment through atmosphe ric deposition from stack emissions or direct injection with sub-surface exhausts. Outboard motor s using the two stroke principle only make a small contribution to the total overall impact compared t o 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 ma y be rained out or washed out of the atmosphere into the sea as well.
The mechanism by which oil or lubricant gets into t he water will play a major part in determining its impact upon the species found within the sea. Oil o r lubricant dispersed below the water line may prov e to have a more toxic effect than if spilled on the surface due to its greater availability to organism s, 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 o n to the shore (particularly mudflats) by tidal act ion.
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 Ir ish Sea and Anglesey, the dark areas indicate regio ns where the surface roughness is less than the surrou nding water. This could be caused by several phenomena including wind shadows, phytoplankton blo oms 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 c an 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 intermitten tly.6

Figure 1. ASAR images of a portion of the Irish Sea and Angl esey. 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 b y oil or lubricants on the surface lessening the su rface 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 ti dal excursion although several parallel tracks can be seen on the edges of the dark region. The right han d figure is a separate image of the region around t he 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. Gurio n, M.Sc. Thesis, 2003).

There are many different modes of action by which a n oil or lubricant may adversely affect species and these include:

1. Direct toxicity of oil or lubricant components, esp ecially to the liver and kidneys in mammals and fish, but also to the phytoplankton at the bottom o f the food chain through reduction in photosynthesis. This may result in a reduction of f ood 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 m ay be through bioaccumulation or bioconcentration of compounds over a long period of time.
3. Indirect effects induced through the increased Bioc hemical Oxygen Demand (BOD) from the organic matter. Bacteria may degrade the organic co mpounds and use oxygen at a faster rate in this process than it can be resupplied from the atm osphere 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 a bility to pass oxygen across membranes.

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

The latter three effects might be common to both na turally derived and mineral oils, while the first t wo effects, essentially the most toxic effects, may be confined to mineral oils. Modes 1 and 2 are also relevant to lubricants discharged in operation, whe re 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 cr ude oil cargoes or in regions of restricted water exchange.

Lubricants consist of blends of base oils and addit ives, each with their own distinct chemical behavio ur. It is, therefore, important to understand the chemi cal behaviour and environmental impact of all lubricant components (base oils and additives) rele ased into the marine environment. The key aspects regarding the environmental impact of chemicals rel eased into the sea can be broadly divided into thre e categories:

• Biodegradation – the potential for a substance to b reak down in the environment due to biological action: is the chemical going to break down rapidl y into harmless components in the sea?

• Bioaccumulation – the tendency of a substance to pe rmeate fatty tissue and enter the food chain: is the chemical going to accumulate in the fatty tissu es of organisms and enter the food chain?

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

All three aspects are directly related to the chemi cal structure of the molecules and so different formulations with different compositions will have different environmental effects in both the long an d short term.
This report reviews the environmental risk and fate of different types of base oils, which form the ma jor part of the lubricant, on the basis of their biodeg radability, toxicity and bioaccumulation potential. Additives to the base oil are also addressed briefl y. Base oil types When formulating a lubricant, it is necessary to ta ke into consideration the intended application of t he lubricant and the physical properties of the base o il 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 lev el and a more effective product.

Conventional marine lubricants use a mineral oil ba se which is refined from crude oil. Occasionally synthetic hydrocarbon base oils are used, such as p olyalphaolefins (PAOs) or polyglycols (PAGs), which are again ultimately derived from crude oil. Altern atively, esters can be used as base oils and are frequently used for “biodegradable” lubricants. The se may be naturally derived ( **e.g** . rape seed, coconut oil, sunflower oil) or produced from petrochemical bases. All biologically sourced oils, whether anima l or plants derived, are termed oleochemicals and this t erminology will be used throughout. Practically, th e majority of oleochemicals are from vegetable oils.8

The base oils have been divided into groups by the American Petroleum Institute (API) according to the ir 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 dif fers which will determine the viscosity. The synthe tic oils derived from petroleum still only make up a sm all proportion of the total and the biologically ba sed 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 r aise environmental concerns regarding the sustainability of source raw materials (Appendix Th ree), although this is not dealt with in detail in this review.

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



## 2. Assessment Approach Published values for each of the toxicity, bioaccum ulation and degradation rates are used where possible although data are not always available in the published scientific literature and remain with in grey literature or the commercial sector. This revi ew primarily considers the environmental properties of lubricants based on the different types of base oil available. For the purposes of this review, bas e oil types are divided into their specific chemical grou ps, as follows:

Petrochemicals

1. Alkanes from partly refined crude oil. 2. Alkanes from highly refined crude oil; these tend t o have a narrower size range than the partly refined alkanes above. 3. Polyalphaolefins (PAO) synthesised from highly refi ned components of crude oil. 4. Polyalkylene Glygols (PAG) also synthesised from hi ghly refined components of crude oil. 5. Esters with component exclusively derived from high ly refined crude oil components.

Oleochemicals

1. Esters synthesised with components derived principa lly 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 a nd comparative performance is used where necessary. Toxicity has been reviewed by considerin g the direct toxic effects of the chemicals on test biota. These tests may be either acute or chronic i n nature but are expressed in terms of the amount o f chemical required to kill 50% of the test organisms . Bioaccumulation has been reviewed by reference t o the water solubility and uptake into fatty tissue i n 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 restrict ed water exchange. The BOD associated with lubricant d egradation may reduce the available oxygen in the water; this is of particular concern in harbours an d 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 degradabil ity of the base oil rather than the direct chemical toxicity.10



### Additives As well as the base oil, there are a range of addit ives in lubricants. Due to their diverse nature, it is beyond the scope of this report to cover these in a ny 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 m ost lubricants are additives which enhance the performance of the product by increasing the contac t 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 antioxida nts, rust inhibitors, viscosity modifiers, or surfactants.11



## 3. Degradation and Biodegradation of Base Oils The major component of any lubricant is the base oi l which may be obtained from a range of sources, including mineral and naturally-derived oils. The b ase oils may be a simple cut taken from the source material or may be synthesised from refined compone nts; each composition will behave differently and have a range of environmental outcomes, depending o n 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 conventio nal mineral oil-based lubricants are alkanes in the C 15 to C 50 range derived from crude oil. The base oils are no t 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 i nitial alkane loading of 150 g.l -1 , 37% of the compounds were degraded in seven days. GC-MS analys is of the cultures of the bacteria **Rhodococcus** had ketones, alcohols and aldehydes present, confir ming 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 t he non-degradable components, as the shorter chain compounds are metabolised (see Figure 4).



### C 15



### C 25

Figure 3. Alkanes of 15 and 25 carbons that may be present i n base oils of this type.
Some of the carbon present in the alkanes would bec ome 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 comp ounds are most readily degraded followed by acids, straight chain alkanes, aromatics, and final ly branched chain compounds. It is this differentia l degradability that leads to the characteristic hump of unresolved complex mixture (UCM) in the gas chromatograph (GC) profile of weathered oil which c ontains these branched materials. An example of weathering oil in the form of a GC trace can be see n in Figure 4.

Figure 4. Change in gas chromatograph profile with weatherin g (from Philp and Kuder, 2008). In the initial figure, the alkane profile is readily appar ent, peaking at a relatively short chain length of C 12 . After weathering, the short chain alkanes have been lost and there is a shift in the peak alkane in the samp le to more waxy compounds (C 28 ). After four months, a large Unresolved Complex Mi xture (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 manufactu re 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 mono mers and have chain lengths up to 50 carbons long. It is possible to choose the chain length for a lub ricant application, so high purity compounds tend t o be the result for this base oil type. It is also likel y that there will be side chains (branched structur es) which have some of the longest degradation times of any g roup of hydrocarbons.
Some industry studies (INEOS 2 ) demonstrate that the shorter chain polymers with low viscosity degrade more quickly than the higher viscosity PAOs which m ay have longer chain lengths and more branching. Their results also indicated that degradation was s low within the first 21 days (<20%) and only achiev ed greater than 50% degradation after 40 days. There w as also a stepwise change in the degradability, wit h only the two lowest viscosity products exhibiting g reater than 50% degradation over the timescale of the test. Therefore, only the lowest viscosity prod ucts would pass the OECD degradability test althoug h a considerable amount would still remain in the env ironment as 51% is still a pass. 

### Polyalkylene (PAGs) and Polyethylene Glycols (PEGs) in Lubricants Polyalkylene glycols (PAGs) and polyethylene glycol s (PEGs) are also synthesised from refined mineral oil components and fall into the petroleum sourced grou p 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 w ill 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/Dura syn%20Environmental%20Bulletin%202009.pdf14

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 repeat ing sub-units, n. In general, the longer the carbon chain, the lower the degradability. Long chain comp ounds with high molecular weight may also be nondegradable but may also be excluded from bioaccumul ation 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 replacem ents for crude oil-derived base oils may be based on esters with several different carbon chain lengt hs and structures. In some cases it is possible to used unmodified naturally-derived oils which are made fr om three fatty acids esterified to glycerol (triacylglycerol or triglycerides); this is the nat ural state of fatty acids in most vegetable seed oi ls. The generic structure can be seen in Figure 7 with thre e side chains of myristic acid (C 14 ).

O O O O

O

O

Figure 7. Trimyristin, three C 14 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 suite s 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 unsaturat ed compounds ( **e.g.** Canola oil). A summary of several common biological ly sourced fats and oils can be seen in Table 3. Rapeseed oil (including Canola) is most frequently used in base oil formulations (LLINCWA, 2003). Ther e are performance issues ( **e.g** . oxidation and thermal stability) with vegetable o ils related to the degree of unsaturation in the fatty acids and the overall sta bility of the lubricant. This would lead to the add ition of more additives into the lubricant formulation to reduce the degree of oxidation and extend the operating temperatures. However, if in the sea, the se 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.15Table 3Fatty acid composition of several vegetable oils and animal fats which may be used as lubricant baseoils. The Sat / Unsat ratio gives anindication of the degree of total unsaturated fattyacids in the oil or fat (Mudge**et al.**, 2008).Oil / FatSat /UnSat10:012:014:016:018:018:1ω918:2ω618:3ω3Beef Tallow0.9--324194331Butterfat (cow) 0.5 3 3 11 27 12 29 2 1Canola (rapeseed) Oil15.7 - - - 4 2 62 22 10Cod Liver Oil 2.9 - - 8 17 - 22 5 -Coconut Oil0.1647189362-Corn Oil 6.7 - - - 11 2 28 58 1Cottonseed Oil2.8--122319541Flaxseed Oil 9.0 - - - 3 7 21 16 53Lard (Pork fat) 1.2 - - 2 26 14 44 10 -Olive Oil4.6---13371101Palm Oil 1.0 - - 1 45 4 40 10 -Palm Kernel Oil0.24481683152-Peanut Oil 4.0 - - - 11 2 48 32 -Safflower Oil10.1---721378-Sesame Oil 6.6 - - - 9 4 41 45 -Soybean Oil5.7---11424547Sunflower Oil 7.3 - - - 7 5 19 68 116

Synthetic esters
Another synthesised ester used as a base oil is tri methyolpropane (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 solubil ity (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 7 00 Daltons in molecular weight.

Figure 8. One of the many biologically sourced ingredients t o 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 c ommon degradation pathway for these compounds. Details can be found in Appendix Four but is essenc e, an enzyme will cut the side chains of the centra l part of the molecule and then remove two carbon sub units at a time. These carbons are then converted to either CO 2 or biomass. One of the key features of these and r elated compounds is the presence of the carboxylic acid group (-COOH) which provides a “han dle” for the metabolism of these compounds by biological enzyme systems. This group will also inc rease the water solubility of the molecule. In many systems with esters of fatty acids such as triacylg lycerol, 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 a n 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. The se compounds will be rapidly degraded in the environment as the fatty acids provide the route fo r C 2 removal ( β – oxidation) as part of the acyl – CoA pathway. Essentially, anything that has an oxygen a tom in the molecule will shorten the degradation time, increase water solubility and facilitate a mo re 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 este rs 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 induct ion in the presence of esterified fatty acids is co

metabolism of compounds such as alkanes that usuall y take longer to degrade by themselves. Laboratory experiments and mesoscale box trials hav e 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, gen erically these are easier to pass then marine biodegradation tests due to the higher concentratio n of microorganisms being present in the inocula. Seawater typically contains 10 3 - 10 8 cfu.ml -1 (colony forming units) and river water typically 1 0 6 - 10 7 cfu.ml -1 . Ideally, at least 10 8 cfu.ml -1 are required to get a consistent biodegradation re sult, assuming18

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 t he OECD method 306, the base oils produced with either crude oil-derived or partly biologically der ived (the fatty acid component) components, degrade by these methods; however, these two groups will ha ve different degradation rates in the first few day s due to the larger number of enzymes needed to degra de 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 degradatio n percentages for mineral oil and biologicallyderived base oil components. In the longer term, mo st of the alkanes of the oil may be degraded by thi s route, but the fatty acid esters with TMP may be pa rtly 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 ov er 56 days due to the refractory nature of some longer chain components.

The structure of the OECD tests for degradability h ave end points which will miss the differential behaviour between the base oils; the mineral oils c omprised 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 initi al rates were very different and the amount remaining at some stage in the future can also be d ifferent.
In general, compounds that degrade quickly will hav e a smaller overall environmental impact than those that persist for long periods of time. In this rega rd, the OECD test used to assess degradability has end19

points at 28 and 56 days. It may be possible for a compound to pass this test in terms of the amount o f 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 t imes. A good summary figure has been produced by (Battersby, 2000) (Figure 11) which demonstrates th e 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 ra tes (CEC L-33-A-93 test) for the different base oil types. From (Battersby, 2000).

Base oils made from mineral oil and biologically-so urced hydrocarbons may nominally pass the OECD test and degrade to “acceptable levels” within 28 o r 56 days, although of the different types, the fat ty acid esters will degrade faster in the short term a nd have a smaller residual component. This degradability is good from one standpoint in that c ompounds will be converted to biomass or CO 2 and “removed”, although in doing so, oxygen will be con sumed. In the general respiration equation (Equation 1), the organic matter (represented by CH 2 O) 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 a s in some coastal areas with poor flushing. If signif icant amounts of degradable organic matter are20

introduced, the bacteria may well remove the organi c matter and the oxygen at the same time. This rate might exceed the rate at which new oxygen is suppli ed across the atmosphere – water interface, especially if there is a film of oil present. This whole process may be compounded by readily degradab le matter from fish processing and other industrial di scharges, surface water runoff and combined sewer overflows entering the water mass as well. Poor wat er quality in terms of oxygen saturation may lower the diversity in the water mass. These oxygen deple tion effects may be considered as indirect toxicity effects due to degradability of the compounds rathe r than a direct chemical effect on an organism. 

### Degradation & Biodegradation: Conclusions

Table 4 shows that ester based oils have a much gre ater 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 bioaccumula tion potential. Minerals oils with straight chain alkane s 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 b ut within that period, several different processes may have occurred. At present, a compound that pass es the 50% threshold may be considered a pass but if 49% then remains and it does not degrade fur ther, 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

Readily22



## 4. Toxicity The chemical composition of the final lubricant pro ducts is a key factor in determining its direct tox icity, as is the manner in which it is used and the enviro nment that receives the material. It is possible to reduce the impact that a product has by altering th ese conditions. In the case of lubricants, the majo r factor will be the choice of chemicals used in the product formulation, as the environmental and usage aspects will remain essentially constant between pr oducts.
Mineral oil toxicity is dependent on the quality an d fraction of oil used. Fractions with higher concentrations of aromatic constituents are more to xic than those without and within the alkanes, the shorter chain will be more available and, therefore , more toxic to biota. Tests frequently use the Wat er Accommodated Fraction (WAF) as only these component s 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 a nd non-toxic in the environment. However this may n ot take into account the indirect effects of vegetable oil polymerisation. For example, after a spill of sunflower oil in the marine environment, the oil po lymerised forming a stable material that bound the intertidal sediments together. The resulting mixtur e was stable for a considerable period of time (Mudge, 1997). Subsequent experiments indicated a v ariety of pathways for the degradation of this vegetable oil, and there was indirect toxicity asso ciated with the formation of an impermeable cap ove r 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 w hether the oil went down the degradation or polymerisation route (Pereira **et al.** , 2003a) which may be controlled by numerous factor s including the quantity of oil in the environment and the degree o f unsaturation of the fatty acids. Indirect toxic e ffects are possible due to the polymerised oil isolating t he sediments from the atmosphere and causing the area underneath to become anoxic. The BOD associate d with the degradation of the compounds can cause the same effect. 

### Testing for Toxicity of Marine Lubricants When testing for toxicity, methods should be select ed that represent the relevant trophic levels in th e marine food chain. Typical test methods used are:

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

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

• PARCOM method 1995 - Protocol for Fish Acute Toxici ty test,

• PARCOM 1995 - A sediment bioassay using an amphipod

.23

Using freshwater toxicity data may not may not accu rately reflect the toxicity of a substance in the marine environment. The degree of correlation betw een freshwater and saltwater species is influenced by the three main factors (Wheeler **et al.** , 2002):

• biological differences between saltwater and freshw ater organisms,

• chemical differences in each medium, especially spe ciation and bioavailability,

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

There is also a misconception that food grade addit ives are always safe to use in the marine environment. Many finished products that claim to b e “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 t oxicity is not of concern. Marine algae can be far more sensitive to a chemical than a human as their physi ological mechanisms for dealing with toxins are ver y different. 

### Toxicity - Conclusions In general, the oleochemical base oils have a low t oxicity towards marine organisms (Table 5) with the LC 50 for fish toxicity reported as being ~10000 ppm for fatty acid esters and glycerol esters (LLINCWA, 2003). Similarly, the polyol esters based on TMP an d adipinic or oleic acid had LC 50 of ~5500 ppm. As with many oily chemicals, the toxicity in some test s is not measureable as the LC 50 exceeds the water solubility of the compound. In such cases, it is po ssible to induce physical effects such as smotherin g but this is not a chemical toxic effect. Some methodolo gies 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 enti re 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 th e potential for bioaccumulation. This toxicity is independent of the degradation rate of the compound s (especially additives) and final products where there may be synergistic effects. Objective measure s can be made between competing products with standard methods.
The presence of additives is dependent on the choic e of base oil and the intended function of the lubricant. However, several of the more toxic compo unds in formulations are also the ones with poor degradability. The overall product toxicity may be significantly reduced by switching to a biological lysourced base oil if used in conjunction with the us e 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

Low25



## 5. Bioaccumulation The process of bioaccumulation is the build-up of c hemicals within the tissues of an organism over tim e. 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 high er exposures to that chemical over time. If the chemic al 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 po tential, either through not being taken up as readily or by degrading more quickly both in the en vironment and in the organism.
The bioaccumulation potential of a compound is dire ctly related to its water solubility as chemicals t hat 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 th e type of atoms in the molecule and compounds comprised solely of carbon and hydrogen tend to hav e the lowest solubilities in water. This group includes the alkanes which form almost 90% of the c urrent base oil in normal lubricant formulations. The inclusion of one or more oxygen atoms to a mole cule will, in general, increase the water solubilit y and, therefore, lead to reduced bioaccumulation pot entials. Compounds with oxygen also tend to be degraded more quickly in the environment or are exc reted 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 an d 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 hydrog en 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 illus trates how the molecular configuration and presence of oxygen affects the water solubility. It would be expected that the bioaccumulation potenti al 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 (K OW ) is often used as a proxy for bioaccumulation potential.

Compound Number of oxygen atoms Water Solubility

(mg.L -1 ) Log K OW

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 a t all while the mineral oil was found in all samples. In this study of drilling mud s, effects could be seen 12 km from the initial sou rce for the mineral oils and they related this to the overa ll adverse effects on the biota.
It has been assumed for some time that larger molec ules 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 formulat ions, 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 bee n several criteria proposed over the past few years t o describe the point at which chemicals are no long er taken up in the body and bioaccumulated (Arnot **et al.** , 2010). The major physical properties that have been used previously are the maximum molecular diam eter or the effective molecular diameter, the octanol – water partition coefficient (K OW ) or water solubility and the molecular mass.
In an evaluation of data for esters, there was a st rong link between the log K OW and the log Bioconcentration Factor (BCF) while the other facto rs had less well-defined relationships. The selecti on criteria chosen by the Canadian Government and Unit ed Nations Environment Programme (UNEP) (Canada, 2000; UNEP, 2001) and the United States En vironmental Protection Agency (USEPA, 1999) led to cut-off log K OW values of ~5. Of the 300 chemicals studied, only 1 2 appear to be greater than the European Union’s preferred value of 700 Daltons. Wh at is clear from this review is that there is no si ngle criterion to adequately describe the BCF and a holi stic approach integrating several factors including measured uptake and elimination rates has been prop osed by Arnot et al. (2010).27



### Testing for Bioaccumulation of Marine Lubricants The two most common test methods for establishing b ioaccumulation potential are OECD 117 and 107. The test substance is added to a mixture of octanol and water and its dissolution in each phase detect ed using generally gas chromatography or an infra red detector. The bioaccumulation of the substance is measured by establishing its partition coefficient (expressed as log K ow ) 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 disso lve in the octanol rather than the water. Therefor e, the greater the log K ow , the greater the likelihood that the substance wil l bioaccumulate.

Partition coefficients for the marine environment a re normally measured on a log scale between 0-6. Substances with log K ow <3 are deemed not to bioaccumulate and those with log K ow >3 are deemed to be bioaccumulating.
Seawater may increase the likelihood of uptake by o rganisms 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 bioaccumulatio n potential in the marine environment. The use of the se test methods as an indicator of a substance’s bioaccumulation potential can negate the need to ca rry out **in vivo** or **in vitro** fish or mussel testing.



### Bioaccumulation - Conclusions In summary, the level to which a component of the p roduct 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 incorpora ted into an organism and some will be metabolised within the organism) as well as the lip ophilic 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 co mponents 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 bas e oil types (Table 7).28

Table 7. Summary of bioaccumulation potential of the differ ent 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

No29



## 6. Additives in Marine Lubricants Although this report reviews the fate of the base o il components of marine lubricants, it is important to consider these ingredients as the different base oi ls demand different suites of additives in the fina l product formulation. Additives have many functions and may be necessary for the product to work as described; the quality of the base oil directly aff ects 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 prope rties of the lubricant.
The greatest proportion of additives are found in e ngine oil formulations which contain large amounts of detergents which also act as an alkali reserve to n eutralise acidic combustion products **e.g.** sulphonates, phenates and salicylates. Dispersants, anti-wears, anti-oxidants and corrosion inhibitors are also add ed. These formulations may also be used in other applic ations and most notably engine oils are commonly used as stern tube lubricants. These lubricants rea dily emulsify with water, which may affect their toxicity, with the additive component readily avail able 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 sour ced from biological materials, these could be considered environmentally sustainable themselves. Indeed, some clothes detergents and liquid laundry products market themselves on this basis by sourcin g the alkyl part of the surface active agent from vegetable oils. These compounds will have appreciab le water solubility by definition and can frequentl y be degraded rapidly in the environment. Polyethoxyl ates are less likely to have a biological source compared to alkyl sulphates although the first biol ogically sourced ethoxylate was announced in the fi rst quarter of 2010.
Many trace additives (<1%) are relatively small (<7 00 Daltons) and have measureable toxicity toward lower level food chain organisms but not towards fi sh. Despite being present at low concentrations in the lubricant, the additives used in some formulati ons may continue to have a deleterious effects on t he basis of a combination of their high water solubili ty (K ow >4 in most cases), low molecular weight, and slow degradability as measured by the OECD methods.
The chemical composition of these compounds indicat es that there may be biologically-derived alternatives ( **e.g** . succinic acid with a single fatty acid as an este r) although there would need to be some fine-tuning of the chain length in order to satisfy performance requirements as well as providing desirable K ow 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 emu lsify and not produce a sheen. This is not surprisi ng as the base oil, whether from natural or oil based sources, will still produce sheen, unless the visco sity 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 s heen to assist in noticing a loss, but in the case of the loss of lubricants from the stern tube, emulsificat ion of the lubricant at the propeller prevents exce ssive lubricant forming sheen under seal failure conditio ns, 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 o f being detected by satellites.
A summary of major factors, biodegradation, toxicit y and bioaccumulation potential, for each of the base oil types can be seen in Table 8. In this tabl e, 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 de grade, 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 m ajority 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 oil s derived from oleochemicals degrade faster and have a smaller residual, do not bioaccumulate appre ciably 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 biol ogically sourced materials.31

Table 8. Comparative environmental behaviour of lubricants based on the base oil type. The biodegradation rate refers to aerobic degradation m easured 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 compo nents that have a reduced environmental impact. Even within the biologically sourced or partially b iologically-sourced components, there are differenc es 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 im pact. The current OECD tests are useful but with en d points of just 28 and 56 days, improvements are req uired to establish the longer term effects.32

Base chemicals comprising alkanes currently have th e largest share of the market and yet also have the slowest degradation rates, greatest potential for b ioaccumulation 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 b est in these regards. The opportunity now exists fo r a shift in base oil composition as products with be tter environmental credentials fulfil all the roles that lubricants are currently used for.
It is widely accepted that all forms of base oil de rived 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 bio logical sources are still ultimately better in the long term. One caveat may be the rapid loss of readily d egradable 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 e xample 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 satell ite images (Figure 1) though quantifying the magnitude of individual routes will require near real time satellite images to guide sampling transects. Surfa ce waters could be collected and gas chromatographi c analysis would be able to identify and quantify the losses. This could form an important research proj ect that demonstrates the current situation and delimit s 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 ove r time.
All the mineral oil components are generally more t oxic than the biologically sourced base oils and although it may be argued that concentrations of th ese 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 leve l inputs may shed light on these deleterious effect s, if present. Linked to toxicity, is the potential fo r bioaccumulation which is related to the chemical structure, water solubility, degradation and depura tion rates. Although there are some questions about the exact cut off between chemicals that can bioacc umulate 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 e nvironmentally 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 one s that have the slower degradation rates (<20% in t he OECD tests and classed as persistent) and may be mo re 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 toxic ity. In some cases, the chemical structures lend themselves to substitution with biologically-derive d 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 environment al performance **i.e** . high biodegradability, low toxicity and low bioaccumulation potential. Howeve r, selecting a base oil with good technical33

performance should reduce the total additive load n eeded 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 meth ods employed should reflect this. This however should not be to the detriment of their technical p erformance, as any environmentally responsible lubricant should have at least the same technical p erformance as a conventional product. This will he lp ensure that equipment functions efficiently, minimi sing failure. An environmentally responsible lubricant with good technical performance will mini mise the potential for any leaks, however, in the event of an incident will minimise the environmenta l impact of any lubricant leaked into the sea.34



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### APPENDIX ONE. Lubricant pathways from shipping to the Marine Envi ronment
Lubricants from shipping make their way into the ma rine 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 s ystems may be drained, refilled or levels topped up

. Many small spills occur when handling oils during t hese operations. All of this oil will make its way into the scuppers and over the side of the vessel, formi ng 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 ru dder shaft bearing, tunnel or azimuth thrusters use d for manoeuvring or propulsion, and horizontal stabi lizers on passenger ships. In these systems, the lubricant is maintained at a higher pressure than t he water outside (to prevent ingress) and is separa ted by an elastomer seal. Normal operation sees a gradu al discharge across barrier seals into the sea. Lubricants used in these systems generally form emu lsions 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 l eakage occurs and no oil film is evident on the wat er surface. This discharge takes place, to a greater o r lesser degree, all the time that the vessel is af loat. It is not obvious, unlike a spill from the deck and is , therefore, often overlooked.
Within the machinery spaces of a vessel are the eng ines and ancillary equipment such as air compressors, hydraulic systems, pumps, **etc** . These are in a sealed environment so spills and l eaks should not be able to make their way into the sea. Engines contribute to discharges into the environment in another way, however. Four-stroke en gines use a sealed lubricant system where the lubricant is re-circulated and has a long service l ife. 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 be ing part of a closed crank case system, the lubrica nt is directly injected into the engine cylinder to lubri cate and seal the piston. There is evidence (Tang e t 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 environm ent by this route. This is also true of small outboard motors, although this constitutes a small loss compared to the larger fixed engine installati ons. 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 machin ery spaces should not normally be able to make its way into the sea since in the event of a spill or l eak it goes into the vessel’s bilge, where intercep tors capture the oil and separate it from bilge water wh ich is discharged overboard. A large volume spill o r equipment malfunction, however, could potentially o verwhelm an oil interceptor resulting in a spill.37



### APPENDIX TWO. American Petroleum Institute (API) grouping of lubr icants

Table A1. The five major base oil groups according to the AP I together with their market share. Groups I, II and III are cuts of refined mineral oil and grou p IV is synthesised from mineral oil precursors. On ly group V contains non-petroleum based oils along wit h 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 9.338



### APPENDIX THREE : Sustainability Of Sources
Renewability of the components in lubricant formula tions, especially the base oil, has an indirect environmental impact. Sourcing of renewable base s tocks from verified sources can minimise the overall environmental impact of the lubricant. The re is a perception that incorporation of biological ly derived materials into products has a lower CO 2 charge and does not deplete scarce resources like crude oil. There is some debate as to the benefit of usin g vegetable oils instead of mineral oils, depending on how they are produced (Mudge, 2008). Full life-cycl e analysis of individual sources and processes may be appropriate in the medium term to assess the ove rall sustainability of using vegetable sources. However, there are benefits from using renewable ma terials rather than non-renewable crude oil in the long term.

Crude oil-derived ingredients are not renewable exc ept on geological timescales and cause environmental damage during the prospecting, extrac tion, transportation, storage and refining phases. In contrast, biologically-derived materials are ren ewable on human timescales, are carbon neutral or have a small carbon footprint, but may also cause e nvironmental issues with the extraction, transportation, storage and refining phases - as wi th crude oil. It has been argued in the past by som e vegetable oil producers that their products are les s damaging than crude oil and they had sought an exemption under the US Oil Pollution Act (1990), bu t this was denied by the US Environmental Protection Agency based on the behaviour of vegetab le oil spills in the marine environment (Mudge, 1995).39



### APPENDIX FOUR. Physical Processes for the Biodegradation of Oils i n the Marine Environment
Once in the marine environment, all oils may underg o 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 other s 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 t ype of oil spilled. For instance, light mineral oil s and refined fuels will undergo substantially more e vaporation, spreading and solubilisation than heavy crudes, vegetable oils and bunker fuel oils. For ma rine lubricants, the formulations have different properties and the two major release scenarios (ont o the surface of the water or sub-surface) will lea d to a range of rates for each process. A schematic d iagram summarising the timescales for the major processes can be seen in Figure A2. Subsurface loss es through stern tubes, for example, will emulsify quickly and tend to settle out of the water column and reach the benthos. Therefore, the surface relat ed processes will not occur and the sub-surface ones w ill 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. (Fro m ITOPF 3 )

In any surface spill, the oil or lubricant will spr ead across the surface of the water; the rate at wh ich 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 wate rs, the temperature extremes are ~5°C – 25°C (Nygard & Dring, 2008). At low temperatures, oils a nd lubricants will be considerably more viscous tha n at warmer temperatures and will spread much more sl owly.
The compounds on the surface of the water may be ex posed to the air and sunlight. Some of the hydrocarbons in the oil may react with oxygen in th e presence of sunlight to form either water soluble products or tars which may persist longer than the original compounds 4 . 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 depend ent on the chemical composition of the oil or oilderived product as the light short chain hydrocarbo ns will evaporate considerably more quickly than th e longer chain, more waxy components. The rate of los s of compounds to the atmosphere will also depend on the film thickness and, therefore, the sp reading 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. Lubrican t base oils are normally of a limited range of hydroc arbon chain lengths and are not volatile. Evaporati on is not likely to be a significant factor when consi dering 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 fractio n 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 DEGRADATI ON AND BIODEGRADATION OF OILS IN THE MARINE ENVIRONMENT
Degradation may occur through pure chemical process es, **e.g.** oxidation, but the most active processes are performed by micro-organisms in the water colum n or in the sediment. Seawater naturally contains a wide range of bacteria which are able to metaboli se oil and the compounds within oil as a carbon source (energy supply). However, oil hydrocarbons a re not the most readily available carbon source and require a series of enzymes to be induced before th e process can begin. This accounts for the delay in the start of biodegradation. Examples of one biodeg radation pathway (among many) that may occur on alkanes can be seen in Figure A3 and on aromatics i n 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. Ste ps 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 wit hin one month as shown here, although some of this loss may not be to biomass and CO 2 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 per iod of the OECD methods. Some ring structures and large complex chemicals are very resistant to degra dation and these compounds may persist for many years. A good example of such a group is the steran es and terpanes present in crude oil and frequently used as biomarkers to identify the source of the or iginal crude oil spillage (Wang & Brown, 2008). The se chemicals generally resist weathering and persist i n the environment for many years.
The fatty acids present in some base oils will unde rgo a series of degradation steps, depending upon t he chemical structure. In the case of most esters, the first stage would be the induction of a lipase enz yme to cleave the fatty acid from the rest of the molec ule. Once free, the fatty acid would undergo chain shortening through β -oxidation, another enzymatic process. The net resu lt of this process is the removal of two carbon subunits from the fatty acid sequenti ally 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 t he alkyl chain diminishes.



### + 2 CH 2 

### β -oxidation process OH O

OH O


### + 2 CH 2 

### β -oxidation process OH O

OH O

Figure A5. A summary of the β -oxidation process acting upon the closest two carb ons to the carboxylic acid group. The resulting smaller compounds are, in general, more water soluble than the parent compounds.