Oil In Sediments Research Articles

Biodegradation of Fuel Oil Under Laboratory and Arctic Marine Conditions

The aerobic biodegradation of the components of a fuel oil under Arctic summer conditions follows a pattern that is indistinguishable from that exhibited under temperate conditions. Straight chain alkanes and small aromatics are degraded first, followed by branched alkanes and larger and alkylated aromatics. We present data on the biodegradation of heptadecane as a representative n-alkane, pristane as a representative iso-alkane, and naphthalene, phenanthrene, and chrysene and their alkylated forms as representative two-, three- and four-ring aromatic hydrocarbons. In particular, the pattern of degradation of the alkylated aromatics allows the identification of biodegradation in samples collected from the field and the estimation of the extent of biodegradation that occurred in the In-Situ Treatment of Oiled Sediment Shorelines Field Trials.

In-situ Treatment of Oiled Sediment Shorelines

Experimental oil spill studies were conducted to quantify the effectiveness of selected in-situ shoreline treatment options to accelerate natural oil removal processes on mixed-sediment (sand and pebble) shorelines. At each of three distinct shoreline sites, treatment test plots and control plots were established within a 40-, 80- and 143-m continuous stretch of oiled shoreline. A total of 5500 l of oil was deposited along a 3-m wide swath in the upper intertidal zone at each site. Approximately one week after oiling, a different treatment technique was applied to each plot. The treatment techniques were: sediment relocation (surf washing), mixing (tilling), bioremediation (fertilizer application), and bioremediation combined with mixing. One plot at each site was monitored for natural attenuation. The quantity of oil removed from the plots was measured six times up to 60 days post-treatment and then again one year later. Changes in the physical character of the beach, oil penetration, movement of oil to the subtidal environment, toxicity, and biodegradation were monitored over the 400-day period. The results verified quantitatively that relocation of oiled sediments significantly accelerated the rate of oil removal from the shoreline by more than one year. Microscopic observations and image analyses confirmed that the oil–mineral aggregate formation process was active and was increased by sediment relocation. Oil biodegradation occurred in this arctic environment, both in the oiled sediments and on the fine mineral particles removed from the sediment by natural physical processes. The biodegradation of oil in sediment was significantly stimulated by simple bioremediation protocols. Mixing (by tilling) did not clearly stimulate oil loss and natural recovery in the context of this experimental design. None of the treatment techniques elevated toxicity in the nearshore environment to unacceptable levels, nor did they result in consequential alongshore or nearshore oiling.

Response of estuarine meio- and macrofauna to in situ bioremediation of oil-contaminated sediment

Numerous studies have demonstrated the efficacy of bioremediation for enhancing oil removal but the ecological effect on shoreline biota is unclear. Therefore, a field experiment was designed at an intertidal sandflat in SW England to assess the effects of nutrient addition to oiled sediments on meio- and macrofauna for a period of up to 45 weeks. Natural assemblages were exposed to different types of experimental treatments (no oil, oil alone, oil treated with slow-release fertiliser or liquid fertiliser). Bioremediation stimulated the microbial population and increased oil biodegradation. This, however, did not result in faster recolonisation rates of fertilised versus non-fertilised oiled sediments. Mild effects of oil and bioremediation treatments on benthic fauna were observed, including short-term shifts in dominance patterns. Decreased abundance of dominant species in the oiled compared to unoiled sediments resulted in significantly higher evenness of benthic assemblages within the first 11 weeks of the experiment.

RAPD-PCR AMPLIFICATION OF DNA FROM VIRGIN OLIVE OIL

The characterization of the genetic identity of DNA recoverable from olive oil could facilitate the identification of the source cultivar. This requires that intact DNA or large fragments suitable for amplification by polymerase chain reaction (PCR) should be recovered from olive oil. This paper presents the preliminary results of an experiment evaluating the extent to which DNA recoverable from the veiled virgin olive (cv. Carolea) oil would allow PCR amplification useful for random amplified polymorphic DNA (RAPD) fingerprinting. Only residual DNA from olive oil sediments obtained by protease treatment was useful in RAPD-PCR amplification.

Microbial Population Analysis as a Measure of Ecosystem Restoration

During a controlled oil spill study in a freshwater wetland, four methods were used to track changes in microbial populations in response to in situ remediation treatments, including nutrient amendments and the removal of surface vegetation. Most probable number (MPN) estimates of alkane and aromatic hydrocarbon degraders showed divergence of the alkane and aromatic degrading populations during the first summer of the experiment. Alkane degraders increased in all plots by 1.5 orders of magnitude and aromatic degraders increased in oiled plots by 3.5 orders of magnitude. Phospholipid fatty acid (PLFA) analysis of biomass and community composition showed no essential differences among treatments. Denaturing gradient gel electrophoresis (DGGE) analysis of the sediment microbial community showed some differences in specific populations of organisms with respect to oiled and unoiled plots. Some organisms were only found in the oiled plots. Sediment toxicity measured against single celled algae showed that the oiled sediments were toxic into the second year of the study, but that nutrient addition relieved the toxicity more rapidly than natural attenuation of the oil.

Bioavailability to Fish of Sediment PAH as an Indicator of the Success of In Situ Remediation Treatments at an Experimental Oil Spill

A weathered medium crude oil was applied to experimental plots of Scirpus pungens (Three-square Bulrush) in a freshwater wetland to determine the efficacy of strategies for shoreline oil spill bioremediation based on nutrient enrichment (bioremediation) and plant growth (phytoremediation). Plots were unoiled, oiled with no added nutrients, or oiled with repeated applications of phosphate and nitrate fertilizers. Following initial treatments, the experimental plots were raked to simulate the activity of wave action on oil penetration, and plants in one fertilized plot were cut repeatedly. The sediments were sampled at regular intervals for 15 months after oiling, and the loss of oil was assessed by 4-day laboratory tests of polynuclear aromatic hydrocarbon (PAH) bioaccumulation by trout, as demonstrated by increases in activity of liver cytochrome P450 (CYP1A) enzymes. Oil alone, oil mixed with sediments in the lab, and oiled sediments from treated plots all induced CYP1A activity relative to untreated controls, indicating the presence and bioavailability of PAH. Induction did not vary with nutrient treatments, but declined by 80% within 15 months of oiling, and chemical analyses indicated equivalent losses of hydrocarbons in sediment. These results demonstrate that bioavailable PAHs persisted in measurable quantities for at least 1.25 years following oiling, and that stimulation of plant growth did not affect the rate of oil disappearance. The controlling factors were likely weathering and sediment movement.

The OSSA II Pipeline Oil Spill: the Character and Weathering of the Spilled Oil

On January 30, 2000, an accidental oil release occurred from a fracture in the OSSA II pipeline where it crosses over the Rı́o Desaguadero in Bolivia, South America. This paper addresses the composition of the spilled oil and the unique weathering processes that occurred after the spill. Samples of oil, oiled sediment, water, and vegetation were collected from the riverbank and surrounding areas for approximately one year after the initial release. The samples were analyzed by gas chromatography with a flame ionization detector and by gas chromatography coupled with mass spectrometry to characterize the weathered product. Laboratory studies were also performed to evaluate the maximum extent of evaporation of the pipeline oil, and the extent of water solubility. Based on these chemical analyses, several conclusions were reached: • There was a rapid and substantial loss of the benzene, toluene, ethylbenzene, and xylenes (BTEX) and polycyclic aromatic hydrocarbons (PAH) oil fractions. • The BTEX and PAH losses were due primarily to evaporation. • The stranded residual oil consisted primarily of heavy, immobile hydrocarbons. • Photooxidation of PAHs, including benzo(a)pyrene, was observed. • A unique weathering mechanism was observed that selectively removed mid-range hydrocarbons (C20 through C39) from the bulk oil. • The overall environmental risk of the spilled oil has been reduced due to the extensive weathering of the oil.

Application of Petroleum Hydrocarbon Chemical Fingerprinting in Oil Spill Investigations––Gulf of Suez, Egypt

In an attempt to examine the suitability of chemical fingerprinting methods in oil spill investigations, multiple parameters sensitive to both sources and degree of weathering were used to characterize spilled oil samples and to distinguish spilled hydrocarbons from sources unrelated to the spill in shoreline of the Gulf of Suez, Egypt. The characterizations of individual aliphatic and aromatic compounds were based on gas chromatography and gas chromatography/mass spectrometry analyses. The distribution of n-alkanes, polynuclear aromatic hydrocarbons (PAHs) and alkyl PAHs in the source oil and an oil slick collected 72 h after the spill were very similar. Major compositional changes observed in a weathered oiled sediment collected nine months after the spill from the shoreline at the spill location were consistent with previous studies. Molecular parameters of hopane and sterane biomarkers were very similar in the source oil, the spilled oil and the highly weathered oiled sediment. The similarity in biomarker compositions provided a strong evidence for a close genetic association of these samples. Ratios of C 2-chrysenes/C 2-phenanthrenes and C 2-chrysenes/C 2-dibenzothiophenes, the pregnane index (sum of the concentrations of C 21 and C 22 steranes over total concentration of steranes×100), and the tricyclic terpane index (sum of the concentrations of C 19 and C 30 tricyclic terpanes over total concentration of terpanes×100) clearly differentiated the refined oil products from crude oils. The composition of bilge oil indicated enrichment of late eluting steranes and terpanes and showed biomarker distributions similar to natural petroleum. The results further support that sterane and terpane biomarker analyses could differentiate oil samples of different sources even though they were sometimes indistinguishable in PAH and alkane compositions.

Formation and Characterization of Oil–Mineral Aggregates

Oil associates with fine mineral particles in an aqueous medium not only as molecules adsorbed onto mineral surfaces, but also as a discrete phase to form microscopic oil–mineral aggregates (OMA). As it promotes the dispersion of stranded oil, this process is now believed to be instrumental in the natural recovery of oiled shorelines and in the efficacy of spill countermeasure techniques such as surf-washing (relocation of oiled sediment into the zone of wave action). To predict the fate of residual oil following spills and the effectiveness of such countermeasures, an improved understanding of the nature and properties of OMA and of the factors influencing their formation is required. Laboratory protocols and microscopical methods have been refined for the detection and classification of OMA. Three OMA types have been identified: droplet, solid and flake aggregates. Droplet aggregates are oil droplets (usually a few μm in diameter) surrounded by individual or flocculated mineral particles. Solid aggregates are mixed oil and mineral bodies of various shapes (scale of tens of μm). Flake aggregates are thin sheets that can reach the mm size range in which mineral and oil are arranged in an ordered configuration. The parameters controlling the quantity, type and size of OMA include mineral type and surface properties, quantity, viscosity and composition of the oil, and oil/mineral ratio. It is also evident that water turbulence (i.e. breaking waves, strong flood currents) greatly enhances OMA formation. Once formed, OMA appear to be very stable structures the buoyancy of which depends on the ratio of oil to mineral in each individual aggregate. OMA being on average less dense than mineral-only aggregates and even buoyant, they will be kept in suspension longer and be dispersed further than unoiled sediment. Mineral particles in OMA act as a surfactant preventing the oil from recoalescing. As OMA formation increases the surface to volume ratio of spilled oil, it prolongs and enhances oil weathering processes such as dissolution, evaporation and biodegradation.

Influence of moisture content and cooking on screw pressing of crambe seed

AbstractThe cooking and drying conditions for oilseeds preparatory to screw pressing are some of the most important factors that influence screw‐press performance. Screw‐press oil recovery, residual oil, pressing rate, and oil sediment content were measured for uncooked crambe seed and crambe seed cooked at 100°C for 10 min, pressed at six moisture contents ranging from 9.2 to 3.6% dry basis. Oil recovery significantly increased (P≤0.01) from 69 to 80.9% and 67.7 to 78.9% for cooked and uncooked seeds, respectively, as moisture content decreased. Residual oil significantly decreased (P≤0.01) from 16.3 to 11.1% and 16.9 to 11.9%, respectively, as moisture content decreased. The reduced oil loss due to only drying the seed from 9.2 to 3.6% was 32% for cooked seed, whereas cooking contributed only 3.6 to 7% reduced oil loss. Pressing rate decreased from 5.81 to 5.17 kg/h and 6.09 to 5.19 kg/h for cooked and uncooked seeds, respectively, whereas sediment content increased from 0.9 to 7.8% and 1.1 to 5.4%, respectively, as moisture content decreased. The effects of moisture content on pressing rate and sediment content were significant at P≤0.05. All relationships of screw‐press performance to moisture content were fitted to a second‐order polynomial.

The Influence of Salinity on Oil–Mineral Aggregate Formation

The formation of microscopic oil–mineral aggregates (OMA) has been linked to the natural removal of stranded oil in coastal marine environments and to the efficacy of surf washing (relocation of oiled sediment into the zone of wave action) as an oil spill remediation procedure. To predict the significance of this process in estuarine and freshwater environments, OMA formation was tested in the laboratory with seawater diluted to obtain a salinity range of 0–35. Quantification of the amount of oil incorporated into OMA shows that the extent of OMA formation is not significantly different from that of seawater for salinity values as low as 1.5–0.15 (1/20 to 1/200 of pure seawater). The precise value of this threshold depends on parameters including oil type and the nature of the mineral present. Below this salinity threshold, there is a linear decrease in the amount of oil incorporated in OMA, to practically zero in distilled water. It is concluded that oil spill remediation by natural or induced OMA formation (i.e. surf washing) is applicable to marine, estuarine and possibly inland hyper-saline environments.

Physical Appearance of Oil in Oil-Contaminated Sediment

The physical appearance of oil was investigated in three types of oil-contaminated sediment: (1) natural harbour sediment, (2) laboratory samples of sediment prepared by simulating the natural oil–sediment interaction processes and (3) laboratory samples of spiked sediment prepared by direct mixing of large volumes of oil and sediment. Microscopic observations show the possible presence of three oil phases in the sediment: (1) distinct oil droplets, (2) oil coating on sediment particles and (3) ‘oil patches’. Through quantitative investigations, it was concluded that the division of oil in the different phases is affected by the oil–sediment interaction processes, oil type, and oil concentration. As far as the droplet phase is concerned, these processes and parameters also influence the droplet size distribution.

Oil Weathering and Sediment Toxicity in Shorelines Affected by the Exxon Valdez Oil Spill in Prince William Sound, Alaska

ABSTRACT Beginning in 1989, scientists supported by ExxonMobil conducted a number of scientific studies to assess the fate and effects of the Exxon Valdez oil spill on shorelines in Prince William Sound (PWS), Alaska. The 1990, 1991, and 1993 field programs included concurrent sediment sampling for hydrocarbon chemistry and sediment toxicity. This sediment quality assessment found that spill residues on the oiled shorelines rapidly lost toxicity through weathering. The relative amounts of naphthalenes and chrysenes in the polycyclic aromatic hydrocarbons (PAH) in the sediments were found to be good indicators of weathering and toxicity. Using a standard sediment amphipod bioassay on the field samples increased mortality above background was found at exposure levels above approximately 2,600 ng/g total PAH (TPAH) for oil that had weathered a year or more. For samples with TPAH > 2,600 ng/g, fractions of naphthalenes (R = +0.76) and chrysenes (R = −0.63) significantly correlated with amphipod mortality where samples with high mortalities (> 80%) were dominated by relatively high fractions of naphthalenes (median = 0.26), and the low mortality category (< 30%) was dominated by relatively high fractions of chrysenes (median = 0.24). The amphipod mortality data fit significantly to a logistic model. Estimated LC10 and LC50 values were approximately 4,100 and 10,750 ng/g TPAH, respectively. Sediment grain size and total organic carbon were also found to contribute to increased amphipod mortality and were covariates in the data analysis. As petroleum weathers through exposure to the environment and lighter hydrocarbon fractions are lost, the results of this study show that the Exxon Valdez spill oil rapidly lost toxicity as the fractions of chrysenes increased and fractions of naphthalenes decreased.

Effect of Bioremediation on the Microbial Community in Oiled Mangrove Sediments

Bioremediation was conducted in the field on a mature Rhizophora stylosa mangrove stand on land to be reclaimed near Fisherman’s Landing Wharf, Gladstone Australia. Gippsland crude oil was added to six large plots (>40 m 2) and three plots were left untreated as controls. Bioremediation was used to treat three oiled plots and the remaining three were maintained as oiled only plots. The bioremediation strategy consisted of actively aerating the sediment and adding a slow-release fertilizer in order to promote oil biodegradation by indigenous micro-organisms. Oil addition stimulated the numbers of alkane-degrading bacteria slightly to levels of 10 4–10 5/g sediment. Bioremediation of the oiled sediment had a marked effect on the alkane-degrading population, increasing the population size by three orders of magnitude from 10 5 to 10 8 cells/g of sediment. An effect of bioremediation on the growth of aromatic-degraders was detected with numbers of aromatic-degraders increasing from 10 4 to 10 6 cells/g of sediment. Active aeration and nutrient addition significantly stimulated the growth of hydrocarbon-degraders in oiled mangrove sediment in the field.

A field experiment of the physical and chemical effects of two oils on mangroves

The effects of two different types and five levels of oil on some physical and chemical characteristics of sediments and plants were investigated in four mangrove species under field conditions. The sediments in which four mangrove species ( Rhizophora stylosa, Rhizophora mucronata, Ceriops tagal and Avicennia marina) were growing, were treated with Kuwait Crude Oil (KCO) and North West Shelf Condensate (NWSC) at application rates of 0, 1375, 2750, 5500 and 11 000 g m −2. The effects varied with species. The oil treatments usually increased concentrations of most nutrient elements in R. stylosa and R. mucronata, had mixed effects on C. tagal and mostly decreased concentrations in A. marina. KCO significantly decreased concentrations of every element examined in A. marina. The effects on sediments also varied with oil type. NWSC decreased concentrations of about half of the elements tested in the sediments and had no significant effect the others. In contrast, KCO increased concentrations of about half of the elements tested in the sediments and had no significant effect on most of the others. The concentrations of hydrocarbons in leaves increased with increasing oil application to the sediments, but the effects varied in the different species. A. marina accumulated between two and six times more hydrocarbons in leaves than the other species. The concentration of hydrocarbons in sediments treated with NWSC decreased by about an order of magnitude in the 24 weeks after application, but the rate of decrease was less for KCO than for NWSC. Sediment pH, dissolved oxygen concentration, redox potential and the salinity of interstitial water were decreased by oil treatments, causing the oiled sediments to become poorly oxygenated with strongly reducing conditions. It was concluded that these experimental oil treatments in the field caused changes in sediment characteristics and uptake of oil components by mangroves, depending on the characteristics of the oil and the mangrove species.

A Field Demonstration of the Efficacy of Bioremediation to Treat Oiled Shorelines Following the Sea Empress Incident

Bioremediation was investigated as a method of treating a mixture of Forties Crude Oil and Heavy Fuel Oil stranded on Bullwell Bay, Milford Haven, UK after the grounding of the Sea Empress in 1996. A randomised block design in triplicate was used to test the efficacy of two bioremediation treatments: a weekly application of mineral nutrients dissolved in seawater and a single application of a slow-release fertilizer. Each treatment supplied an equivalent amount of nitrogen and phosphorus. Concentrations of residual hydrocarbons normalised to the biomarker 17α(H),21β(H)-hopane showed that after two months the oil was significantly (p<0.001) more biodegraded in the treated plots than in the controls. On average, the oil in the nutrient amended plots was 37% more degraded than that found in the controls. There was no evidence that the bioremediation treatments increased the toxicity of the oiled sediment. The results confirm that bioremediation can be used to treat a mixture of crude and heavy fuel oil on a pebble beach. In particular, the data suggest that the application of a slow-release fertilizer alone may be a cost-effective method of treating low-energy, contaminated shorelines after a spill incident.

A Field Experimentation on Bioremediation: Bioren

Most shoreline bioremediation strategies are based on the addition of limiting nutrients to contaminated environments to cause an acceleration of the natural biodegradation process. Before approval for operational use, these products designed to be used in the environment, should be validated in field trials to assure their efficiency in reducing residual contaminant concentrations and toxicity. This paper describes the design, implementation and preliminary results of an experimental field study to evaluate the effectiveness of the bioremediation agents BIOREN 1 and BIOREN 2 of interest to the EUREKA BIOREN program. The agents BIOREN 1 and 2 are proprietary formulations of nutrients synthesised from fish meal and they were proven effective in laboratory studies of the two granular nutrient formulations. BIOREN 1 is unique in that it is augmented with a biosurfactant. To provide equivalent nitrogen concentrations the quantities of BIOREN 1 and 2 added were respectively 10 and 14.4 % of the oil quantity. The results showed a “starter effect” for the formulation BIOREN 1: biodegradation was significantly enhanced during the first five weeks of the experiment; after that the enhancement was weaker and significant differences were not observed between treatments. These results may be attributed to the fact that significant nutrient depletion may not occur in small scale controlled spill experiments. In addition, it has been proven that oxygen availability limited biodegradation. There is a need to develop aeration techniques, such as raking, that aerate the sediment without further burying the pollutant. Final oil balance assessment proved to be very instructive as it is the main practical factor taken into consideration by the operational team: the aim of the shoreline cleaning operation remains to reduce oil sediment content.

The Toxicity of Oil-Contaminated Sediments During Bioremediation of a Wetland

ABSTRACT Inorganic nutrients were applied to oiled wetland sediments during an experiment to assess the effect of enhanced bioremediation on petroleum degradation and toxicity reduction. For a period of 6 months after the controlled application of oil to experimental plots, oiled wetland sediment samples were tested for acute toxicity. The three treatments evaluated were an oiled control, inorganic nutrient addition, and inorganic nutrient addition plus an alternate electron acceptor. Sediment toxicity was assessed using Microtox® and amphipod bioassays. The Microtox® 100% Test detected significant sediment toxicity up to 29 days after oil and treatment application while the Solid-Phase Test detected significant sediment toxicity up to Day 15. The Microtox 100%® Test showed elevated toxicity on Day 8 for nutrient plus alternate electron acceptor plots and reduced toxicity on Day 15 for nutrient plots, relative to oiled controls. The observed decrease in sediment toxicity from the Microtox® assays correlated with petroleum losses. Oiled sediments were initially highly toxic to amphipods with average mortality rates ranging from 86 to 92%. Amphipod mortality decreased significantly 71 days after treatment to between 47 and 28%. However, a significant increase in mortality was observed at Day 140 in plots receiving nutrient amendments, possibly due to elevated ammonia levels.

Evaluating The Addition of Fine Particles To Enhance Oil Degradation

ABSTRACT Natural biodegradation rates of oil within the marine environment are partly controlled by surface availability, as microbial attack primarily occurs at the oil-water interface. Therefore, increasing the surface area of residual oil by the addition of fine oleophilic particles may prove to be an effective bioremediation strategy. Considering commercial availability and cost, heat-treated peat was identified to be a promising particle source as it has high oil absorption properties and does not compete with oil as an alternative carbon source to oil-degrading bacteria. A preliminary laboratory experiment conducted with a respirometry system demonstrated the feasibility of nutrient and peat additions to enhance the metabolic activity of bacteria within oil-contaminated sand beach sediments. Field trials were conducted with similar peat and nutrient concentrations in a north-temperate beach environment with weathered Scotian Light crude oil over a 138-day period. The rates of microbial respiration and productivity were enhanced significantly above unoiled and oiled control sediments with the addition of inorganic nutrients with and without peat amendments. Treatment of sediments with inorganic nutrients and peat did not increase the toxicity of the residual oil. Gas chromatography/mass spectroscopy analysis was used to quantify bioremediation success by normalizing the loss of individual components to the conserved marker 17?(H), 21?H)-hopane. While there is evidence of a stimulatory effect with the addition of peat, results suggest that nutrient availability in the interstitial water limited optimal rates of oil bioremediation.

Optimizing Hydraulic Cleaning Techniques for Oiled Coarse Sediment Beaches: Meso-Scale Field Trials

ABSTRACT The objectives of this ongoing study are to: (1) determine the biological effects on intertidal biota associated with the use of hydraulic cleaning techniques, and (2) develop data on environmentally optimum combinations of hydraulic cleaning parameters for use by oil spill responders. This report presents the initial results of the meso-scale field trials phase of the project. Hydraulic cleaning parameters examined in the meso-scale field trials were: (1) water pressures from deluge to approximately 10.0 psi (69.0 kPa), (2) water temperatures from ambient to 60°C. In 1997, groups of colonized cobbles were collected from a donor beach in Lizzie Cove on Hunter Island, British Columbia, dosed with Bunker C fuel oil, and treated at various combinations of water pressure and temperature. Species monitored included the algae Fucus spp. and Mastocarpus papillatus; the barnacle Balarus glandula, limpets (Lottiidae) and snails (Littorina spp.). Un-treated oiled and unoiled controls were also established. The treated and control sets of cobbles were returned to the original donor beach and allowed to recover subject to natural environmental conditions, including predation and recruitment. Biological observations of abundance and mortality were made immediately post-treatment (48 to 72 hours) and 1 year post-treatment. These data were then statistically compared within treatment groups, between years and to control cobble data. Among the main findings of the meso-scale field trials were: (1) greater mortality at all treatment levels 1 year post-treatment for Fucus spp., Balanus glandula, Lottiidae and Littorina spp. (with some exceptions), than seen immediately post-treatment. Trends in the data over increasing temperatures and pressures seen immediately post-treatment are not apparent 1 year post-treatment; (2) dramatic increases in the percent coverage of Mastocarpus papillatus were observed 1 year post-treatment as compared with pre-treatment coverage, including the unoiled control; (3) 1 year post-treatment, no significant differences were seen between mortalities in the various treatment combinations and the untreated, oiled control for Fucus spp. and Balanus glandula; and (4) preliminary evidence exists that pressure washing of oiled cobbles at high pressures and temperatures has negative effects on recruitment in Balanus glandula.