on Early life Stages of Haddock

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SENSITIVITY OF LARVAE TO DRILLING WASTES (PART B): Effects of Produced Water on Eariy Life Stages of Haddock, Lobster and Sea Scallop

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SENSITIVITY OF lARVAEvTO~ DiRILll~G WASTES (PART B): Effects of.Proau·~'e~FWgte~,on Early life Stages of Haddock, LQbste'r~'ancFSe~fiScallop

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November, 1998

Cranford, P., K. Querbach, G. Maillet, K. Lee, J. Grant and C. Taggart. 1998. Sensitivity of Larvae to Drilling Wastes (Part B): Effects of produced water on early life stages of haddock, lobster and sea scallop. Report to the Georges Bank Review Panel, Halifax, NS, 24pp.

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54 1% of discharge concentration). Produced water is a chronic problem, with the total volume discharged greatly exceeding the volume of hydrocarbons produced. Furthermore, its discharge volumes typically increase as oil/gas reserves are depleted.' Chronic effects on scallop veliger larvae in this study· were limited. The chronic effects on haddock and lobster were not determined due to time and logistical constraints of our small-scale exposure facilities. The gradual ecological change of exposed marine systems resulting from the cumulative effects of all waste streams over the long life of a prod.l:lcing field, and the potential for chronic sublethal effects not measured in the present study could result in significant direct and indirect effects of production activities on fishery resources. This is a complex problem requiring considerably more research on the behaviour, fate and biological effects of produced water than could be accomplished in the short time available for this study. '

November, 1998

ID

Sensitivity of Larvae to Drilling Wastes: Part B

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1.0 INTRODUCTION

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Exploratory drilling for oil and gas has been conducted on the eastern Canadian continental shelf since 1966 and drilling activity is rapidly increasing .as reserves discovered on the Grand Banks and Scotian Shelf are developed for production. In 1987 a proposal was made by Texaco Canada Resources Ltd. to drill two exploratory wells on the Canadian sector of Georges Bank. Georges Bank is one of the most productive marine environments in temperate latitudes and, as a result, it supports a rich commercial fishery. The potential for environmental impacts from routine drilling operations has always been a concern as they inevitably result in a certain degree of pollution. Concerns about the potential risks to the valuable fishery resources resulted in the placement of a moratorium on petroleum exploration activities on the Canadian sector of Georges Bank until January 1, 2000.

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The moratorium agreement between the Canadian and Nova Scotia governments includes a public review of the environmental and socio-economic impacts of oil and gas exploration on Georges Bank. The Panel set up to carry out this review identified several issues that required further study so that any real or perceptual concerns could be addressed in a sound and balanced manner. One such concern was related to the limited understanding of the biological effects of operational drilling wastes on key finfish and shellfish species. Of particular concern was the general lack of knowledge on the toxicity of drilling fluid and produced water effluents to the early developmental stages of these species. Considering that the early life stages of many marine organisms are generally more sensitive to toxicants than adults (Lonning 1977; Britt et al. 1987; Linden 1975; Solbakken et al. 1984; Neff 1987), the potential for significant impacts on future fisheries may exist. Benthic organisms have generally been the focus of research into the environmental effects of offshore hydrocarbon exploration and production activities as the bulk of the wastes discharged from drilling platforms sediment rapidly. A viewpoint commonly held until recently was that impacts on fish should be restricted to the immediate vicinity of the drilling platform. However, fisheries biologists are now reconsidering the potential effects on fish and larvae following recent laboratory and field observations indicating detrimental effects at i much greater distances from drilling platforms than originally envisaged (Cameron and Berg 1992; Stagg and Mcintosh 1996; Raimondi et al. 1997). Similarly" zones of impact on some sensitive benthic species have been observed to extend to much greater distances around drilling platforms than previously reported (Olsgard and Gray 1995). Environmental impacts in regions of extensive oil and gas drilling activities 1ikely result from a combination of effects from the discharge of drilling fluids and production waters. The two types of operational drilling wastes identified by the Panel for study were drilling muds and produced water. The present report addresses the acute and chronic biological effects of produced water. Further research with water-based drilling mud is included in a separate report in this technical report series (Sensitivity of Larvae to Drilling Wastes: [Part AD. Produced water is the largest volume waste stream in the production process and over the life of a producing field' can exceed the volume of hydrocarbons produced by ten times. The formation-water component of production water is a brine which derives its salinity predominantly from the major ions found in seawater. In addition, it also contains a number of metal and organic constituents,

November, 1998

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depending on the nature of the formation from which they are withdrawn and the operations associated with a given facility (GESAMP 1993). The major components of environmental interest include the following: 1) hydrolysis metals, 2) heavy metals, 3) petroleum hydrocarbons, 4) nutrients, 5) radionuclides, and 6) treating chemicals. The hydrolysis metals, predominantly Fe, Mn, and AI hydrolyze readily in seawater to form inorganic metal oxide precipitates. While these precipitates are not toxic they can sequester contaminants within the produced water. The heavy metals most commonly associated with produced water include barium, cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc. While the elevated concentrations of these metals (100-10,000 times seawater) may be reduced rapidly by dilution, many are known to be highly toxic. Following produced wat~r discharge their transport to the benthic environment may be accelerated by adsorption onto particles or co-precipitation with particles. Petroleum hydrocarbons in produced water occur in a dispersed (oil droplets) or dissolved (soluble oil) form at 1000 times the ambient concentration. The hydrocarbon fraction of produced water has been shown to impact the species diversity of benthic communities in the area of shallow water discharges ~Neff, 1987). Elevated concentrations of the naturally occurring radionuclides 210 Pb, 23 U, 234Th and total Ra 26Ra and 228Ra) have been observed in produced waters. Of these, the two isotopes of radium 26Ra and 228Ra) probably make up the bulk of nuclide activity in produced water. In addition to human health considerations, radium is of major interest because of its high solubility, its potential for co-precipitation reactions in produced water, and its tendency to bioaccumulate in food chains. Large quantities of scale/corrosion inhibitors, biocides and emulsion breakers are also added to injection waters that are subsequently discharged in production water.

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Produced water has not been considered a major issue of environmental concern since it was presumed that it would be rapidly dispersed at sea. However, this issue has resurfaced based on observations of impacts on adult and larval fish in the North Sea (see above) and a recent study that has shown that produced water discharges may induce flocculation processes which concentrate the contaminant fraction and accelerate its transport to the benthic environment (Muschenheim et al. 1995). Mesocosm studies of the effect of produced water on several pelagic trophic levels have also observed indirect effects on fish larvae (COR and herring) resulting from direct impacts on phytoplankton and zooplankton (Gamble et al. 1987). To provide key scientific knowledge required for deliberations on the environment impacts associated with the development of offshore oil/gas resources, the Georges Bank Review Panel decided to fund the following research study on the toxicity of operational drilling wastes to early life stages of sea scallop (Placopecten magel/anicus) , lobster (Homarous americanus) and haddock (Melanogrammus aeglefinus). These species were chosen based on their economic importance and the availability of brood stock for concjucting laboratory experiments.

November, 1998

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2.0

MATERIAL AND METHODS

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2.1

Test Organisms

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Fertilized eggs from naturally spawning haddock (Me/anogrammus aeglefinus) were obtained at an age of 24-48 hours from a captive breeding stock maintained by the National Research Council facility at Sandy Cove, N.S., and transferred to an environmental chamber at Dalhousie University. Eggs and larvae were incubated at 8goC in static, 0.2-lJm filtered natural seawater in a 100 L tank with overhead fluorescent lighting that provided a surface irradiance of 25 prnol photons m-2 S-1 on a 12h light: 12h dark photoperiod; The insulated incubation tank was circular, with a black interior, and was covered witb clear acrylic. Aeration was provided with compressed air filtered at 0.2-lJm and passed through activated charcoal. Non-viable (negatively buoyant and opaque) eggs and dead larvae Were removed from the bottom of the tank every 1-3 days. First-feeding larvae were offered cultured algae (Nanochloris spp.) and a marine rotifer (Brachionus plicatilis) ad libitum. Female adult lobsters (Homarus americanus) containing fertilized eggs were collected from Georges Bank by commercial fishers and transferred to a continuousflow, 1500 L tank that Was maintained at ambient seawater temperatures (5-12°C) in the Aquatron facility at Dalhousie University. Adult lobsters were fed ad libitum a dry pellet formulation (Maine Lobster Technology Inc., Hancock, Maine). Adult sea scallops (Placopecten magellanicus) were collected using a commercial dragger from Georges Bank and from a mariculture facility in Chester Basin. Scallops were transferred to a continuous-flow seawater tank maintained at 13°C in the Aquatron facility. Addition of 10 L of the cultured algae T. Isochrysis galbana (T-iso) at 6 1 10 cells ml- was made daily to provide a food source. Spawning of adults was induced by thermal shock (4°C increase in temperature) . The marine diatom Thalassiosira pseudonana was grown at 20°C with an average light intensity of 35 urnol photons m-2 S-1. The light source was provided by a bank of 40W cool-white fluorescent fixtures on ct '16-hour light: 8-hour dark photoperiod.

2.2

Acute Toxicity Evaluations

Several 2 L samples of produced water (PW) from an operational discharge line were collected ln sealed polyethylene containers by PanCanadian Petroleum Ltd. from their CoPan production operations near Sable Island on the Scotian Shelf: The samples were shipped to Dalhousie University and kept at 8-13°C until use in the experimental studies. Acute toxicity test conditions for each species are summarized in Table 1. All tests were carried out in 24 ml glass scintillation vials that were capped with Teflon-lined lids. Before use, all glassware was soaked in 10% HCI for 24 h, rinsed with Nanopure water and dried at 60°C. Produced water concentrations of 0 (control), 0.1, 1, 10, and 25% were prepared using glass volumetric pipettes to dispense the produced water to each vial. All treatments were allowed to weather in filtered seawater for 48-72 h at

November, 1998

6


Table 1. water.

Summary of experimental conditions for acute toxicity tests with produced

Species Condition

Placopecten magellanicus (sea scallop)

Homarus americanus (lobster)

Melanogrammus a eglefin us (haddock)

Test type: Dilution water: Age oj organism:

Static Filtered sea water 1-2 hour gametes 5-7 day veliger

Static Filtered sea. water 7-10 day larvae 14-17 day larvae

Test duration:

gametes - 48 hours veligers - 96 hours 13°G 12 h light:12 h dark

96 hours

Static Filtered sea water 1-4 day embryo (ESE) 8-12 day embryo (LSE) 3~7 day larvae (YSL) 13-17 day larvae (OSL) 96 hours

8°C 12 h light:12 h dark

8°C 12 h Iight:12 h dark

25 0,0.1,1,10, and 25 10 3 24ml 24ml 7-10 day fed 14-17 day not fed none 3 Death

25 0,0.1,1,10, and 25 10 10 24ml 20-24 ml algal cells and rotifers none 3 Death

Oxygen pH Salinity

Oxygen pH Salinity

Temperature: Photoperiod: Light lrradiance (urnol photons m-2 S-1): Dilution (%): No. of Replicates: Organisms/Replicate: Vessel Volume: Water Volume: Feeding: Aeration: Rotations per minute: Effects Measured: Other Measurements:

25 0, 0.1, 1, 10, and 25 10 150.-200 24 ml 24ml T. Isocrysis galbana none 3 Gametes - Fertilization Veligers - Death, Size Oxygen pH Salinity

experimental temperatures before addition of organisms. This period of time was to allow for chemical equilibration of the produced water (including flocculation reactions) prior to exposure to test organisms. This facilitates the simulation of natural conditions encountered with chronic produced water discharges. Ten replicate vials were used for each PW dilution, species and life-stage. Life-stages tested for haddock included early stage embryo (ESE) at 1-4 days old, late stage embryo (LSE) at 8-12 days old, yolk sac larvae at 3-7 days post-hatch (YSL), and older (feeding) stage larvae (OSL) at 13-17 days post-hatch. Lobster larvae tested were in the first stage as described by Aiken and Waddy (1989). Lobster used in tests in which where they were fed a ground dry lobster feed (same as above) were 7-10 days old, while the unfed lobster test was performed on 14-17 day old larvae. Tests with sea scallops were performed on 1-2 hour old sperm SInd eggs and on 5-7 day old veligers.

November, 1998

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The number of individuals added to each vial is given in Table 1. Haddock eggs were individually placed in the vials using soft aluminum forceps while the larvae were added using Pasteur pipettes to reduce stress induced by transfer. Lobster were transferred individually to vials using soft forceps. Scallop embryos, sperm and eggs were added using an Eppendorf Repeater pipette and additional triplicate samples were added to vials containing buffered formaldehyde for determination of initial numbers. At the start of the test, all vials were randomly placed in a rotator that was set at three revolutions per minute for the duration of the experiment to maintain produced water particulates in suspension. All acute toxicity tests were run for 96-h, except for the scallop gamete fertilization test (see below), that was terminated after 48-h as the embryos degraded quickly after death. The oxygen content (Strathkalvin Oxygen Meter fitted with a Radiometer electrode), pH, temperature and salinity (Orion conductivity meter) in vials wa~ monitored periodically during the exposure period. After the incubation period, the vials were removed from the rotator and the numbers of live and dead individuals in each replicate were determined. Mortality for all tests was determined by direct observation using a Wild dissecting microscope. The clarity and buoyancy of haddock eggs was used to differentiate between live and dead embryos as they turn opaque and become negatively buoyant upon death. Both haddock and lobster were assessed for mortality based on examination of heart activity. Sea scallop veligers were evaluated for mortality based on observations of the motility of flagella and cilia, which are normally in continuous motion. To allow for changes in motility as a result of disturbance, ciliary motion was assessed after an initial 1-min waiting period. In addition to determining the lethal effects of each PW treatment on scallop veligers, the effect on growth was determined by measuring changes in veliger size distribution. The size distribution of initial and final samples of scallop larvae from each treatment were determined using a Coulter Multisizer /I Particle Analyzer equipped with a 400-lJm aperture tube. Fertilization success of sea scallop eggs during 48-h incubation of eggs and sperm with each PW concentration was assessed by determining the ratio of the mean number of live veliger larvae in five replicate 0.5 ml subsamples to the estimated number of fertilized eggs (using the preserved samples) added to each vial.

2.3

Chronic Toxicity Evaluations

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Chronic toxicity test conditions for each species are summarized in Table 2. All tests were carried out in 1 L glass bottles that were capped with Teflon-lined lids, Before use, all glassware was soaked in 10% HCI for 24 h, rinsed with Nanopure water and dried at 60°C. Produced water concentrations of 0 (control), 0.01, 0.1, 1, and 10% were prepared using glass volumetric pipettes to dispense the PW to each bottle. All treatments were allowed to weather in filtered seawater for 48-72 h at experimental temperatures before addition of organisms. Duplicate bottles were used for each PW concentration. High mortalities of haddock and lobster control populations during the tests prevented an evaluation of the chronic effects of PW. Sea scallop proved easier to maintain and approximately 13,000, 5-7 day old larvae were added to each bottle by pipette at the beginning of an 18-day exposure period along with the T-iso food source. The bottles were placed on a rotator at 3 rpm for the 18-day exposure,

November, 1998

8


At approximately 2-day intervals, 20 ml subsamples were collected from each bottle for determination of chlorophyll-a concentration (see below), veliger mortality (assessed as above) and preservation in formaldehyde. On days 5, 8, 12, 15, and 18, 80 ml subsamples were collected for veliger size distribution analysis (as above). All subsamples removed from exposure bottles were replaced with a similar volume of seawater containing the PW concentration and fresh T-iso food particles. To assess the potential for indirect effects of PW on finfish and shellfish larvae resulting from direct effects on phytoplankton, a 10-day chronic exposure experiment was conducted with a marine diatom. An inoculum of Thalassiosira pseudonana in an enriched f/2 seawater media (Guillard, 1975) was added to each bottle containing the desired, PW concentration (0, 0.01, 0.1, and 10%). .The bottles were rotated during exposure as above. On every second day of the exposure, duplicate subsamples were collected without replacement for determination of chlorophyll-a concentration, and cellular fluorescence capacity (CFC) using a Turner Designs fluorometer (model 10001). Samples for chlorophyll-a analysis were filtered (Whatman GF/F) and extracted in 10 ml of 90% acetone for 24 h at 20°C before measurement. CFC is a physiological index of relative photosynthetic efficiency, and was· estimated according to Vincent (1980).

Table 2. Summary of experimental conditions for chronic toxicity tests with produced water. Species

Placopeeten magellanicus

Condition

Thalassiosira pseudonana (algae, diatom)

(sea scallop) Test type: Dilution water: Age of organism: Test duration: Temperature: Photoperiod: Light Irradiance (prnol photons m-2 S-1): Dilution (%): No. of Replicates: Organisms/Replicate: Vessel Volume: Water Volume: Feeding: Aeration: Rotations per minute: Effects Measured: Other Measurements:

Static Filtered sea water 5-7 day veliger 18 days 13 °C ; 12 h Iight:12 h dark

Static Filtered sea water 10 days 20°C 12 h light:12 h dark

25

35

0, 0.01, 0.1,1, and 10

0, 0.01, 0.1, 1, and 10

2 18,000 1000 ml 1000 ml (small air space)

T. Isochrysis galbana at 2-day intervals none

3 Death, Growth Oxygen pH Salinity Chlorophyll-a

2

50 IJg Chi L-1 1000 ml 1000 ml (small air space) enriched f/2 media

none 3 Chi-a, Condition (CFC) Oxygen pH Salinity

November, 1998


2.4

9

Calculations and Statistical Analysis

The lethal concentration for 50% of the initial population (LC so) was computed using the Toxstats program (created by Charles Stephan in 1996 and upgraded to Windows by Gary Westlake of the Ontario Ministry of Environment and Energy in 1997). The program computes LC so values using three methods, with theprobit method best suiting our data. LC so values were calculated only when the percent survival in the control populations averaged 90 or above. Prior to conducting statistical analysis all data were tested for normality using the Kolmogorov-Smirnov test in Graphpad Prism (San Diego, CA). Percent (proportional) data generally violated the normality assumption and all data were normalized using an arcsine transformatio-n: arcsin U::j)·s), where P is the proportion in question. Analysis of variance (ANOVA) were used to assess exposure time and/or treatment (PW concentration) effects on biological response variables (survivorship, growth or fertilization success) from acute and chronic exposure experiments. Where significant treatment effects were observed, multiple comparison tests (Bonferroni corrected) were performed to find which treatments were significantly different. The hypothesis tested was that mean response values were equal between treatments. The hazard function as described by Ouellet et al. (1992) was used to compare the percent mortality of scallop veliger larvae between treatments during the chronic exposure. Kruskal-Wallace distribution comparisons were conducted to observe where significant differences occurred between size distributions of scallop veligers and for CFC data from the T. pseudonana chronic exposure. A significance level of a = 0.05 was used for all tests.

3.0

RESULTS

3.1

Acute Toxicity Evaluations "

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Haddock - The percent survival of the four haddock life-stages after exposure to the five PW treatments is presented in Figure 1a. Survival of control (untreated) animals was high (>80%) for late stage embryos (LSE) and yolk-sac larvae (YSL), but was relatively low (-50%) for the eariy-stage embryos (ESE) and older feeding-stage larvae (OSE) (Fig. 1a). Decreased survival for all 'life-stages examined was observed at the 25% produced water (PW) concentration (Fig. 1a). The yolk-sac larvae were particularly sensitive with decreased survival apparent at the 10% PW level (Fig. 1a). LC so values were not calculated for most life-stages owing to less than 90% survival in the controls, but was determined to be 21.8% PW for feeding-stage larvae; One-way ANOVA showed significant effects (P < 0.05) of PW on survival of late-stage embryos, yolk-sac larvae, and older feeding-stage larvae. The early-stage embryo appears to be relatively insensitive as no significant effect on mortality was observed over the experimental test concentration range. The results of multiple comparison tests are shown in Table 3. The late-stage embryo and feeding stage larvae showed significant reductions in survival in

I November, 1998


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November, 1998


4.0

17

DISCUSSION

Acute toxicity test results indicated that the early life stages of haddock, sea· scallop, and lobster are sensitive to produced water (Fig. 1). Very few of the haddock embryos and larvae survived acute exposure to 25% produced water and 96':h LC so values of 22% and 21% were calculated for feeding-stage larvae and scallop veligers, respectively. The 2: 10% concentration resulted in significant mortalities of fed stage one lobster larvae, scallop veligers, and yolk-sac haddock larvae (Fig. 1). For haddock, the most sensitive life-stage tested appears to be the yolk-sac larvae. Although it is not appropriate to calculate an LCso value tor tests in which mortalities in control populations are high, we observed a 50% reduction in the survival of yolk-sac larvaeat the 10% PW concentration, compared to the control (Fig; 1a). The lower sensitivity of early-embryonic stage haddock to PW, compared with older embryos and yolk-sac larvae, may have resulted from protection offered by the egg chorion layer, which can act as an effective barrier against entry of toxic substances. Britt et al. (1987) found that the larval stages of caplin (Mallotus villosus) and lumpsucker (Cyclopterus lumpus) were more sensitive to a toxicant (hydrocarbons) than embryonic stages. However, the relatively large variability in survival data between replicates for earlystage embryos (Fig. 1a) may have limited our ability to detect significant differences in survival between treatments. This greater variability in results for early-stage embryos may have resulted from not completely filling the vial with seawater (20 ml added to 24 ml vial). Consequently in some cases, mortality may have increased as a few larvae were observed to become lodged in the corner of the Teflon-lined lids. The air space was eliminated from all other tests. The relatively high survival of feeding stage larvae in the 10% PW concentration (Fig. 1a) indicates that the acute toxicity of PW is reduced, but not eliminated, as haddock develop. The acute toxicity of produced water to first-stage lobster larvae varied considerably between tests, apparently depending on whether they were starved or fed (Fig. 1b). Significant reductions in the survival of larvae in the 10 and 25% PW treatments were observed only when the animals were provided a diet consisting of a ground dry pellet formulation. The elevated mortalities in tests where food was provided may have resulted from higher metabolic rates' and/or ingestion of produced water contaminants adsorbed to food particles. Direct uptake of contaminants may have resulted in the 96-h LCso value of 0.9% (9,000, ppm) PW, which is suggestive of exposure to a toxic substance «10,000 ppm; Neff 1987). A problem for interpretation of mortality results from the lobster larvae tests is the cannibalistic nature of these animals. Mortalities from cannibalism should beconsistent between the different PW treatments, but prevents us from attributing observed mortalities solely to PW exposure. Relatively little information is available on the acute lethal toxicity of produced water to marine organisms' (Neff 1987). However, the available data show a wide range of toxicity depending on the species tested and the source of the produced water. Schiff et al. (1992) compared the toxicity of three samples of produced water to several species. The most sensitive test was with silversides larvae, Menidia beryl/ina, which gave LC50 values between 1.1 and 5.5% PW. Tests with mysids, Mysidopsis bahia, produced LCso values ranging from 4.9% to 11.4%. The polychaete, Neanthes arenaceodentata, was the least sensitive species with LC50 values between 18.1 and 28.6% (Schiff et al. 1992r Moffitt et al. (1992) tested the toxicity o~ 24 produced water

November, 1998


18

samples using standard sheepshead minnow and mysid tests and found a range of 96-h LC50 values between 2% and 28% PW. Sauer et al. (1997) tested the toxicity of 14 PW samples using the mysid and sheepshead minnow tests and observed LCso values of 5% and greater. Neff (1987) compiled acute toxicity data from previous studies and found observed LCso values to be less than 1% PW in only i i % of 108 samples. It would appear from the relatively high acute toxicity observed for fed lobster larvae (LCso of 0.9% PW), that this species and life stage is sensitive to toxic constituents in produced water. Although only a few species have been used to test the acute toxicity of drilling wastes, lobster larvae have previously been identified as being one of the more sensitive test organisms (Neff 1987). In addition to the reduced survival of sea scallop veliqers during acute exposure _to 10% produced water, other significant effects were observed. The mean size of veligers decreased during exposures to ?:10% PW (Fig. 2a). Examination of individual size distributions indicates that this decrease in mean size was not the result of negative growth, but was caused by selective mortality of larger veligers. It may be that the effects of produced water exposure are only manifested once the larvae grow to a certain size or that it impacts the most metabolically active organisms (i.e. the rapid growers). The scallop fertilization test resulted in significant reductions in fertilization success for the 1% PW treatment (Fig. 1d) and the median effect concentration (EC so) value was estimated at 1% PW. Toxicity testing with sea urchins, Strongylocentrotus purpuratus, based on the fertilization success of eggs after sperm are exposed to PW for 60-min, resulted in a similar toxic response with ECso values between 0.74% to 1.2% for different samples of produced water (Schiff et al. 1992). Krause et al. (1992) conducted tests on the acute effects of PW on S. purpuratus and found that 10-min exposure to 0.0001% (1 ppm) significantly reduced fertilization success, and ranked the sensitivity of early life stages as: sperm> eggs »zygotes. An important observation from that study was that effects resulting from sperm exposure to PW can be delayed and expressed as abnormalities in a later life stage. They concluded that a virtually instantaneous exposure of urchin sperm to low concentrations of produced water reduces fertilization success and that the eggs that are fertilized can manifest impairments later in development. Chronic lethal and sublethal toxicity tests with sea scallop veligers showed significant effects on survival at 10% PW (Fig. 3), which is the same as was observed in the acute exposure (Fig 1c). It appears that prolonged exposure to relatively low « 10%) concentrations of produced water does not increase mortalities of scallop veligers. Based on this fact, the toxic threshold for produced water is between 1 and 10%. Veligers in all treatments except 10% PW showed similar changes in population size at age. (Fig. 2b) and had a similar effect on available food supplies (presumably similar feeding behaviour) as the control (Fig. 2c). However, the apparent decrease in size at age (perhaps reflecting slow growth) after Day 8 of the chronic toxicity test (Fig. 2b) may indicate the presence of a 'bottle effect' that constrained larvae growth in all experimental treatments. The potential for indirect effects of drilling wastes on larvae, that may result from direct effects on their food resources, was investigated by monitoring changes in the biomass and condition of a phytoplankton species during chronic exposure to produced water, Observed changes in the chlorophyll-a concentration and cellular fluorescence capacity (CFC) of the marine diatom T. pseudonana during the exposure were similar for all treatments except the 10% concentration, which produced a significant reduction in

November, 1998

Sensitivity of Larvae to Drilling Wastes: Part

B

19

CFC, compared to the control (Fig. 4). While it is not evident in the chlorophyll-a data, this change in CFC resulting from exposure to 10% PW indicates a reduction in the photosynthetic efficiency of the algal cells that would result in reduced productivity. The reduction in CFC during all treatments is likely related to SUb-saturating light irradiance for this species. Very few studies on produced water toxicity have been conducted with marine plants. Brendehaug et al. (1992) and Stmmgren et al. (1995) examined growth inhibition in Skeletonema costatum exposed to produced water from different sources and reported a range of EC so values from 2.1% to 50% PW. The effects of produced water on marine organisms will depend on actual exposure concentrations and duration at the oil/gas production site. Much of the total discharge occurs during its initial descent throuqh the water column dilution of the as turbulence entrains seawater into the jet/plume. During the initial dissent phase, PW discharges are diluted 1 to 5% in the immediate vicinity of the discharge (Brandsma et al. 1992). Currents and turbulence continue to disperse the waste plume, which is diluted to 0.1 % within 0.5 to 4 km of the discharge (Somerville et al. 1987: Stremqren et al. 1995). Any larvae entrained in the convective descent plume would be exposed to high waste concentrations for only a short period of time. Increasing numbers of larvae will enter the plume during the diffusion phase, but these will also experience limited exposure to PW concentrations that can cause acute mortalities (> 1%). However, contaminants are known to accumulate in the surface microlayer and may also accumulate in convergence zones at tidal fronts. Embryos and larvae may also become concentrated in these zones, increasing their exposure to PW contaminants.

pw.

Although it would appear from the high dilution rate of produced water that there. should be no major effects on larvae (or other pelagic organisms) in high energy offshore environments, it is important to note that this analysis was based on limited acute toxicity data and does not take into account physical/chemical interaction of' produced water (e.g. flocculation) which may alter its transport kinetics. These shortterm tests are useful for detecting immediate biological responses to PW, but discharges over many years might result in substantial contaminant bioaccumulation in some species or subtle environmental changes that could potentially affect fishery resources. The observation that brief exposure of early life stages to low PW concentrations (0.0001 %) could result in a developmental response at a later life stage (Krause et al. 1992) is also not considered in this analysis. Population effects may be realized as a result of induction of chromosomal aberrations and morphological defects. These defects, which have been observed to be widespread in several regions, have been attributed to anthropogenic factors including oil pollution, and may result from exposure of the embryos or their parents to the contaminant (Cameron and Berg 1992). Experimental work has established that a high proportion of these 'abnormal' larvae do not survive. For simplicity and cost considerations, regulatory acute toxicity tests exclude particularly sensitive life stages and/or transition phases that can have a large influence on the future strength of a fishery (Raimondi and Schmitt 1992). Long-term field studies of biologic:al effects provide the best indication of responses to contaminants as the organisms are exposed to all drilling waste streams at environmentally realistic levels for long periods. Field studies have focused primarily on produced water effects on the benthos, and relatively little information is available on possible effects on the life history of pelagic organisms (Neff 1987). Krause (1994) demonstrated that urchins held in cages downcurrent from a produced water outfall suffer a decrease in gamete performance

November, 1998

20


(egg fertilizabillty and sperm attack rate) that is directly related to the distance from the outfall. The potential of produced water from the Scotian Shelf (same PW as used in the current study) to impact sea urchin fertilization has also been confirmed (K. Lee, DFO, unpublished data). Significant effects on performance were detected to a distance of 80 m from the outfall. Raimondi and Schmitt (1992) conducted field experiments on abalone, Haliotis rufescens, larvae and the viability of larvae (based on survivorship, settlement ability and metamorphosis) was reduced at all distances up to 100 m from the PW outfall. Osenberg et al. (1992) studied the growth and survivorship of mussels, Mytilus edulis and M. californianus, held in cages in the water column at different distances from a PW outfall, and detected biological effects to at least 100 rn from the discharge. All of these field studies detected biological impacts at distances from the outfall that were similar to the zone of impact predicted using waste dilution models and acute toxicity data (e.g.; LCso and EGso concentrations of PW predicted within 500 m from discharge): The residual effects on organisms resulting from acute exposure to drilling wastes is a concern and the potential to resolve this issue with available information is quite limited (Boesch et al. 1987). Factors controlling stock recruitment are also poorly known, limiting our ability to predict the consequences of larval mortalities to fisheries. This does not indicate that effects on fisheries are absent, only that with our present data base and knowledge, we are unable to fully address the environmental significance of produced water impacts. It has been suggested that the exposure of sensitive earlylife stages to drilling wastes may be limited by conducting drilling operations during less sensitive periods. This may be difficult to achieve given the limited overlap in the spawning times of important commercial species (Table 4). Larvae of different resource species are present in the water column at most times of the year.

I I I

Table 4. Spawning periods of some commercial species on Georges Bank.

1 Species Lobster Scallop Haddock Cod Herrino

5.0

J

F

M

M

A

J

J

I

A

N

0

S

0

I

Spawn--

-

Spawn Spawn--

sPiwnl

/

I

-Spawn

-

I

- - Spawn-

SYNOPSIS

Acute toxicity Jests, generally based on a 96-h LC so (lethal concentration to 50% of the test population) protocol, have characterized produced water as slightly toxic (LC so = 0.1 to 1% PW) to practically non-toxic (LCso = 1% PW) (Neff 1987). These studies are generally conducted using a few standard species that are readily maintained in the laboratory (e.g. mysids, sea urchins, amphipods, sheepshead minnows). However, it is evident from the studies that have been conducted on a variety of marine organisms that the acute toxicity of produced water is highly species-specific (Neff 1987; Schiff et al. 1992). The sensitivity of or~anisms to toxins also depends on

November, 1998

I I I I (, ,

I,

~

1 oJ

:J


21

developmental stage, with early-life stages identified as particularly. susceptible to mortalities (Lonning 1977; Britt et a/. 1987; Linden 1975; Solbakken et al. 1984; Neff 1987). LC50 thresholds for the different haddock, lobster and sea scallop life-stages tested in the present study were comparable with the range of toxicity observed for other marine organisms. Stage one lobster larvae were the most sensitive with an observed LC50 of 0.9% PW. Feeding stage haddock larvae and scallop veligers were the least sensitive with a LCso value of approximately 22%. Inherent sensitivity of some early-life stages resulted in mortalities of laboratory control populations that exceed established "classical" lab-based criteria for assessing biotest results for regulatory compliance. Nevertheless, considering their economic importance, and that impacts were observed with increasing produced water concentrations, this factor should not preclude the use of important resource species and sensitive life stages for assessinq the potential for anthropogenic impacts. An integration of results from acute toxicity tests, drilling waste dispersion/dilution models and field observations suggest that impacts from produced water discharges to high energy offshore environments may have a highly localized impact on invertebrate and fish larvae. It is important to note that these analyses 'does not consider the potentially important chronic environmental effects of PW discharges or the cumulative biological effects that may result from exposure to mixtures of drilling wastes. Under current financial, logistical and time constraints, the present study was not able to examine the potential for impacts on the entire life history of important resource species. Critical stages and transition periods may have been missed and limited information is available in the literature that can be used to alleviate all concerns related to potential impacts on fisheries. Of particular concern is the limited knowledge of the persistence of biological effects resulting from short-term exposure to drilling wastes, residual effects that may not be manifested until a later life stage, and lethal and sublethal effects resulting from chronic exposure. Until further research into these topics has been conducted, a precautionary approach is recommended for the management and regulation of offshore drilling activities.

6.0

ACKNOWLEDGEMENTS

'. This study was sponsored by the Georges Bank Review Panel through a joint project agreement between Fisheries and Oceans Canada and the Oceanography Department of Dalhousie University. The combined efforts of researchers with a broad range of expertise permitted this ambitious project to be conducted on limited funding in a short period of time. Thanks are extended to Dave Knickle of Adams and Knickle Ltd. for providing adult sea scallops from Georges Bank. Mike Dadswell of the Great Maritime Scallop Trading Co. Ltd. also provided live scallops. Female lobsters containing fertilized eggs were collected by Captain Richard Aitkinson and the crew of the F.V. Ryan Atlantic on behalf .of Continental Seafoods Ltd. Fertilized haddock eggs were provided by Dr. Stewart Johnson and Brian Blanchard of the National Research Council. We also thank Steve McKenna of NRC for advice and assistance with spawning of scallops.

November, 1998


7.0

22

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"

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