The effects of used ferrochrome lignosulphonate drilling muds from a Santa Barbara channel oil well on the development of starfish embryos

The effects of water-soluble fractions (WSF) of thirteen used ferrochrome lignosulphonate muds on developing embryos of Patiria miniata were studied. The muds were collected during the drilling of a single slant well from Platform Hondo in the Santa Barbara Channel, California, at drilling depths of 4220 to 9858 ft. None of the embryos survived 48 hours' exposure in 25 % WSF of the muds (25,000 ppm mud added (v/v)). Significant reduction in growth and high abnormalities (up to 100%) were observed in the 15% WSF. In lesser concentrations the effects varied from significant reduction of growth, down to 0·5% for three muds, to significant enhancement of growth for several muds in some dilutions. The EC₅₀'s ranged from 5% to greater than 15% WSF. In the 5% WSF, decreased embryo growth was correlated with increasing Cr concentrations and possibly also with total organic carbon (TOC). Although experiments carried out with NaOH addition to simulate the strong alkalinity of the muds showed increased abnormalities and decreased embryo growth with increasing pH, in the chemically complex WSF (5% dilution) the opposite effect occurred. Dissociation of chrome lignosulphonate molecules from particulates may occur with increasing acidity and explain the relationship between pH and toxicity in dilute WSF. The results of these experiments are discussed in terms of the effects of dispersions of drilling muds in the oceanic environment. It is concluded that water column effects on organisms during the dumping of such muds are only likely within short distances of the discharge pipes of offshore drill rigs.     

Comparative toxicity of drilling muds: role of chromium and petroleum hydrocarbons

Samples of used drilling muds collected during the course of a single well drilling operation exhibited different degrees of acute toxicity to sheepshead minnows and grass shrimp. For moulting grass shrimp, Palaemonetes pugio, the 96-h LC₅₀'s were 360 to 14 560 ppm (μl/litre); many of these values were considerably lower than those reported from previous drilling mud assays. However, when some of the muds used in this study were tested on sheepshead minnows, Cyprinodon variegatus, the resulting 96-h LC₅₀'s (6300 to 100 000ppm) were well within the range of previously reported values.Although a number of the drilling mud samples had relatively high amounts of chromium due to the addition of sodium chromate, there was a low correlation between chromium concentration and toxicity. In only three drilling muds could chromium content alone account for the observed toxicities. Furthermore, chemical analyses revealed the presence of No. 2 fuel oil like petroleum hydrocarbons in the mud samples. Based on the results of toxicity tests with No. 2 fuel oil and the concentrations of oil present in the muds, the toxicity of the mud samples to grass shrimp appears to be largely attributable to the petroleum hydrocarbon content.     

Acute toxicity of a used chrome lignosulphonate drilling mud to several species of marine invertebrate

The acute toxicity of a used seawater chrome lignosulphonate drilling mud to several species of marine annelids, crustaceans and molluscs was evaluated. The medium density mud (13·4 lb/gal, 1·57 kg/litre) was composed primarily of seawater, bentonite clay, chrome lignosulphonate, lignite, sodium hydroxide and barium sulphate. The toxicity of four mud/seawater preparations was determined. These were the layered solids phase (LSP), the suspended solids phase (SSP), the unfiltered mud aqueous fraction (MAF) and the filtered mud aqueous fraction (FMAF). Four species each of marine annelids and bivalve molluscs and five species of marine crustaceans were evaluated. The median lethal concentration of the MAF (96-h LC₅₀) varied from 32 to > 100% MAF for the different species. The FMAF was slightly less toxic than the MAF. Adult polychaetes, Neanthes arenaceodentata and Ctenodrilus serratus, one-day old juveniles of opossum shrimp, Mysidopsis almyra, and four day zoeae of grass shrimp, Palaemonetes pugio, were the most sensitive to the MAF. Juvenile N. arenaceodentata, adult polychaetes, Ophryotrocha labronica, and three bivalve molluscs were highly tolerant to the MAF. The SSP preparation at concentrations of 10-20 ml/litre was toxic to post-larvae and juveniles of the commercial shrimp, Penaeus duorarum and P. aztecus, respectively. Exposure to the LSP preparation caused greater than 50% mortality amongst adult N. arenaceodentata, juvenile and adult coquina clams, Donax variabilis texasiana and adult scallops, Aequipecten amplicostatus. Other species tested were quite tolerant. A sublethal response observed was the inhibition of reproduction in the marine annelids, Dinophilus sp. and Ctenodrilus serratus. Toxicity of the mud aqueous fractions appeared to be due primarily to volatile soluble organic materials in the extract, whilst that of the SSP and LSP preparations appeared to be due to the smothering action of fine particulates in the mud. Based on the results of this investigation and published observations of solids concentrations in the water column during drilling mud discharge, it is concluded that discharge of a used chrome lignosulphonate drilling mud, such as that used in the present investigation, from offshore platforms is not likely to cause measureable damage to benthic, demersal or pelagic marine animals.     

Abrasive effects of Mount Saint Helens ash upon epidermis of yolk sac larvae of Pacific herring Clupea harengus pallasi

Larval Pacific herring Clupea harengus pallasi were exposed for 24 h to suspensions of estuarine sediment and volcanic ash from 0 to 8000 mg/litre. The effects of these suspensions on the epidermis of the yolk sac larvae were determined using light and scanning electron microscopy. Examination of the epidermis at specific locations on dorsal and ventral body surfaces showed that the effects were apparent with increasing concentrations of both sediment and ash. The effects of volcanic ash, however, occurred at lower concentrations and were of greater magnitude than those of sediment. Examination of the epidermis of these larvae under the scanning electron microscope revealed puncture-type damage associated with volcanic ash but not estuarine sediment. Thus, in addition to the possible effects of smothering which may occur with fine particulates, the ash particles result in direct mechanical damage to the delicate early larvae. The concentrations where effects were noted were greater than those likely to be observed in the lower Columbia River estuary where the larval herring occur. In upriver locations characterized by higher suspended particulates, delicate larvae of other species may suffer epidermal damage.     

Mixed-function oxygenases as biological monitors around petroleum hydrocarbon development sites: Potential for induction by diesel and other drilling mud base oils containing reduced levels of polycyclic aromatic hydrocarbons

The use of oil-based drilling muds has been discouraged in hydrocarbon exploration and production in the marine environment but these muds are presently being used to a considerable degree in the United Kingdom and Norwegian sectors of the North Sea. Field studies in the North Sea have demonstrated only localized impacts around individual drilling sites,^1,2 even including those sites where ‘toxic’ diesel oils were employed as base fluids in drilling muds. Yet the question of disposal of cuttings contaminated with oil from drilling muds remains somewhat controversial. The induction of mixed-function oxygenases (MFO) has been validated on a number of occasions in the field as a sensitive index of low level hydrocarbon exposure (reviewed by Payne),³ including sites in the North Sea where diesel-based muds were used.⁴ The present study demonstrates that any potential for induction by hydrocarbon contaminated cuttings will probably be reduced by substitution of low-aromatic base oils for diesel in drilling mud formulations.     

Time and density-dependent properties of fluid mud suspensions,NE brazilian continental shelf

Fluid mud suspensions, defined as containing between 10 to 480 g/liter, occur in numerous estuarine and nearshore continental shelf environments. The quantities of sediment incorporated in fluid mud are enormous, and they must be considered to be of major importance in the transport and deposition of fine-grained sediment in these environments.This study was performed on the NE Brazilian Continental Shelf, a muddy coastline that reaches from the Amazon to the Orinoco, a distance of 1600 km. The fluid mud forms a thick (3 to 5 m) boundary layer that extends 100-km offshore and generally coincides with the 10-m depth contour.The fluid muds appear well-adjusted to the current regime on the NE Brazilian continental shelf. Near-bottom current velocities were seldom greater than 50 cm/sec during the sampling interval. Consequently, yield stress in fluid muds of 1.20 × 10³ kg/m³ and greater was seldom exceeded, and consolidation proceeded without interruption.     

Exploring ecological changes in Cook Inlet beluga whale habitat though traditional and local ecological knowledge of contributing factors for population decline

The Cook Inlet beluga whale, one of five Alaskan stocks, is genetically distinct and geographically isolated from other populations. Historically, Cook Inlet whales were hunted commercially, for sport, and for subsistence uses. The Marine Mammal Protection Act (MMPA) of 1972 ended commercial and sport hunting; in 1999, subsistence hunting voluntarily ended. In 2008, Cook Inlet beluga whales were listed as endangered under the Endangered Species Act after annual aerial surveys indicated the population was not recovering as expected. A combination of natural and anthropogenic factors may be affecting this population’s recovery. This study documented traditional and local ecological knowledge of Alaska Native subsistence hunters and fishers and commercial fishers through participatory research to explore ecological changes in Cook Inlet over time and to identify potential factors impacting this beluga whale population. Study results identified potential environmental and climate change factors including prey competition, health of beluga and their prey, and the presence of killer whales, the majority of which may indicate an ecosystem regime shift in the Cook Inlet region. Human-related factors included fisheries management and related prey reduction, water contamination, and anthropogenic-related noise. These results corroborate identified threats to beluga whales and also identify potential new areas of scientific investigation and management. As such this study demonstrates the value of incorporating traditional and local ecological knowledge into ongoing science and management.     

Parallel structure among environmental gradients and three trophic levels in a subarctic estuary

We assessed spatial and temporal variability in the physical environment of a subarctic estuary, and examined concurrent patterns of chlorophyll α abundance (fluorescence), and zooplankton and forage fish community structure. Surveys were conducted in lower Cook Inlet, Alaska, during late July and early August from 1997 through 1999. Principle components analysis (PCA) revealed that spatial heterogeneity in the physical oceanographic environment of lower Cook Inlet could be modeled as three marine-estuarine gradients characterized by temperature, salinity, bottom depth, and turbidity. The gradients persisted from 1997 through 1999, and PCA explained 68% to 92% of the variance in physical oceanography for each gradient-year combination. Correlations between chlorophyll α abundance and distribution and the PCA axes were weak. Chlorophyll was reduced by turbidity, and low levels occurred in areas with high levels of suspended sediments. Detrended correspondence analysis (DCA) was used to order the sample sites based on species composition and to order the zooplankton and forage fish taxa based on similarities among sample sites for each gradient-year. Correlations between the structure of the physical environment (PCA axis 1) and zooplankton community structure (DCA axis 1) were strong (r = 0.43-0.86) in all years for the three marine-estuarine gradients, suggesting that zooplankton community composition was structured by the physical environment. The physical environment (PCA) and forage fish community structure (DCA) were weakly correlated in all years along Gradient 2, defined by halocline intensity and surface temperature and salinity, even though these physical variables were more important for defining zooplankton habitats. However, the physical environment (PCA) and forage fish community structure (DCA) were strongly correlated along the primary marine-estuarine gradient (#1) in 1997 (r = 0.87) and 1998 (r = 0.82). The correlation was poor (r = 0.32) in 1999, when fish community structure changed markedly in lower Cook Inlet. Capelin (Mallotus villosus), walleye pollock (Theragra chalcogramma), and arrowtooth flounder (Atheresthes stomias) were caught farther north than in previous years. Waters were significantly colder and more saline in 1999, a La Niña year, than in other years of the study. Interannual fluctuations in environmental conditions in lower Cook Inlet did not have substantial effects on zooplankton community structure, although abundance of individual taxa varied significantly. The abundance and distribution of chlorophyll α, zooplankton and forage fish were affected much more by spatial variability in physical oceanography than by interannual variability. Our examination of physical-biological linkages in lower Cook Inlet supports the concept of “bottom-up control,” i.e., that variability in the physical environment structures higher trophic-level communities by influencing their distribution and abundance across space.     

An assessment model for the fate and environmental effects of offshore drilling mud discharges

The benthic boundary layer transport (bblt) model was developed to assess potential impact zones from drilling mud discharges from offshore oil and gas drilling. The model focuses on the drift, dispersion and concentration levels of the suspended fraction of the drilling mud fines in the benthic boundary layer with the assumption of a spatially homogeneous environment. The current version of the model includes a wave boundary layer, a breakup module for drilling mud flocs, a dose–response module for scallops, and a graphical user interface (GUI). The GUI was written in Java which makes the code largely platform independent. Simulations of suspended barite concentration near Sable Island on the Scotian Shelf during drilling in the fall of 1999 reproduce the very low concentrations (generally less than 1 μg L⁻¹) observed during the Environmental Effects Monitoring program. However, the simulations also exhibited concentrations in excess of the no-effects concentration for scallops (100 μg L⁻¹) prior to the sampling program. The model estimates that the potential impact on scallops in the vicinity of the drilling is a few days of lost growth over scales of a few kilometers.     

饵料对锯缘青蟹大眼幼体生长发育的影响

以不同比例的轮虫和卤虫无节幼体搭配成各种饵料组合，分别喂养不同发育期的锯缘青蟹幼体，重点研究大眼幼体的存活、生长发育、变态和干重及化学元素(C、H、N)含量的情况.结果表明饵料搭配得当，适时适量的投喂，其幼体的生长发育和变态都正常，并可获得较高的存活率，若饵料搭配不当不仅会导致幼体出现高死亡率，而且还能诱发发育期变化的现象；不同饵料搭配对大眼幼体干重及化学元素(C、H、N)含量的影响很显著，相差60％～70％，约一个发育期，而这差异可以通过该期幼体投喂足量卤虫无节幼体来加以弥补，大眼幼体的C、H、N占干重的百分比仅次于溞V，这表明青蟹幼体在这两次变态前需在体内积累高比例的有机营养物质来保证变态的顺利进行.     

潮间带盐沼植物黏附悬浮颗粒物的差异性研究

为了研究潮间带盐沼植物黏附悬浮颗粒物的差异性,在长江口选择了三种盐沼植物群落对它们黏附的颗粒物质量进行测定,结果表明:(1)植物群落距潮沟或光滩越近,生长位置的滩面高程越低,则黏附颗粒物越多,而在盐沼前缘单位滩地面积上植物黏附颗粒物的质量以1%~3%/m(单位水平距离)的速率从水体悬浮颗粒物含量相对较高的盐沼外缘光滩或潮沟向盐沼内部减小;(2)植物黏附的颗粒物量在垂向上从上到下急剧增大,通常在靠近滩面5~10 cm的部分植物的黏附量占植物黏附总量的三分之一以上;(3)相邻群落单位滩地面积的互花米草[(220.6±172.7)g/m2]的总黏附量明显多于芦苇[(64.9±38.1)g/m2]和海三棱藨草[(45.2±31.7)g/m2],而按单位生物量来说单位滩地面积上三种盐沼植物黏附的颗粒物以海三棱藨草最多[(150.5±134.8)g/kg],芦苇最少[(28.8±22.8)g/kg],互花米草介于两者之间[(57.5±32.9)g/kg];(4)海三棱藨草的黏附量在季节上差异性明显,秋初(9月)是春末(5月)的6倍,在冬季该植物消失,其黏附颗粒物的功能也消失。造成盐沼植物黏附悬浮颗粒物差异的根本原因是生物量、悬浮颗粒物含量和淹没条件(淹没的深度、时间、频率)的不同。     

The influence of particle size of the dispersed mineral fraction on the settlement of marine and estuarine muds

Considering the sedimentation behaviour of suspensions, four states of different sediment-water mixtures are usually distinguished, these being (in increasing concentration) dilute suspensions, concentrated suspensions, fluid muds and mud deposits. As the concentration values delimiting these states vary considerably from one cohesive sediment to another, a procedure for their quantitative determination is proposed here. This paper deals mainly with the effects of hindered settling in interacting concentrated suspensions and of sedimentation in fluid muds. In contrast to the settling velocity of individual particles in a dilute suspension, which must be studied statistically as a stochastic variable denoted W, hindered settling and sedimentation velocities can be described by a scalar denoted V, as solids at any particular level of concentrated suspensions and fluid muds settle at the same velocity. On the basis of settlement tests carried out in this study and published data on organic-rich cohesive sediments, a concentration-dependent empirical law for a permeability coefficient (k) has been generated for cohesive sediments, using data from ten estuarine and nine marine environments, based on the one-dimensional Kynch theory of sedimentation. Based on the median diameters of the dispersed mineral fraction, the main provenances of the sediments are: fine to very fine clay from tropical marine/estuarine environments, medium clay to very fine silt from estuaries in western France, and fine to coarse silt from marine (harbour) environments in the Normandy region of France. A general trend for the influence of the grain size of the mineral fraction on the permeability coefficient has been established. It is demonstrated that the concentrations delimiting the different states of sediment-water mixtures can also be related to the grain size of the mineral fraction. Thus, hindered settling and sedimentation processes of muds, similar to the marine and estuarine cohesive sediments considered in this paper, can be studied as generic problems parameterized through a defined median diameter of the dispersed mineral fraction. Results for Loire estuary sediments are presented separately, based on specific tests to analyse the influence of experimental conditions on settlement. Moreover, the concentration values delimiting the different sediment-water mixture states have been largely established for this estuary.     

暂养底质对小刀蛏亲贝生长和存活的影响

本研究比较了混合泥、池塘泥和海沙三种底质对小刀蛏亲贝生长和存活的影响。利用粒度仪测定三种底质粒度,混合泥和池塘泥粒径分别为49. 01pm和52. 18μm,海沙粒径为285. 84μm。在三种底质中暂养30d后,混合泥和池塘泥组小刀蛏的存活率均为60%,显著高于海沙组的6. 67%;混合泥和池塘泥组小刀蛏的干重特定生长率分别为4. 87%/d和4. 37%/d,均显著高于海沙组;混合泥和池塘泥组小刀蛏的体长特定生长率分别为2.34%/d和2.03%/d,同样均显著高于海沙组的1. 1%/d;三个实验组的小刀蛏肥满度都有所增长,混合泥和池塘泥中小刀蛏的肥满度分别为35. 74%和35. 79%,较初始时增长显著,海沙中小刀蛏肥满度为32. 98%,增长不显著。综上所述,混合泥和池塘泥更适于小刀蛏亲贝的暂养。本研究优化了小刀蛏亲贝的暂养条件,为小刀蛏人工育苗技术提供理论支持。     

Hindered settling velocity of cohesive/non-cohesive sediment mixtures

New methods are proposed for predicting the hindered settling conditions encountered by concentrated suspensions containing mixtures of sand particles and mud flocs. These methods, based on two-fraction formulations, are developed by consideration of the settling characteristics of monodisperse and polydisperse solid particle suspensions applied to cohesive/non-cohesive mixtures of mud flocs and sand particles. The behaviour of these predictive methods is evaluated over a wide range of mixture conditions and compared with existing formulations, with their parametric dependence on the relative volumetric concentrations and floc/particle sizes for the mud and sand constituents established. The results indicate that consideration of the full return flow effects generated by both fractions provides the best modelling framework for predicting the hindered settling conditions over a wide range of sand–mud mixtures.     

拟穴青蟹大眼幼体和第Ⅰ期仔蟹底质选择的研究

拟穴青蟹大眼幼体和仔蟹对海泥和泥沙底质的选择性显著高于各种粒径的沙底（粒度0.06～2.00mm）.其原因可能与海泥和泥沙底质在流动海水中物理稳定性高于沙砾有关.通过以埋栖选择性和相对埋栖率为指标考察了大眼幼体和仔蟹的栖息方式,发现白昼大眼幼体埋栖在底质中的比例显著高于夜间,也高于仔蟹;夜间大眼幼体栖息方式与仔蟹差别不明显;并发现大眼幼体栖息方式存在着昼夜差异和昼夜节律性.这揭示了拟穴青蟹大眼幼体对底质的选择性和在底质上栖息的方式表现出对FTT机制的适应.     

Spatial distribution of the crab larvae (Decapoda: Anomura et Brachyura) in Possyet Bay (Peter the Great Bay of the Sea of Japan) in 2000–2001

The analysis of the data obtained during the plankton surveys in Possyet Bay (Peter the Great Bay of the Sea of Japan) in 2000–2001 is presented. The larvae of eight crab species were registered in the plankton: the red king crab Paralithodes camtschaticus (Tilesius, 1815), the snow (opilio) crab Chionoecetes opilio (Fabricius, 1780), the Arctic lyre crab Hyas coarctatus ursinus (Leach, 1815), the kelp crab Pugettia quadridens (de Haan, 1839), the helmet crab Telmessus cheiragonus (Tilesius, 1815), the Japanese swimming crab Charybdis japonica (A. Milne-Edwards, 1861), the pea crab Pinnixa rathbuni (Sakai, 1934), and the porcelain crab Pachycheles stevensii (Stimpson, 1858). These species belonged to six families: Lithodidae, Atelecyclidae, Majidae, Portunidae, Porcellanidae, and Pinnotheridae. The role of the variability of some of the hydrological factors in the meroplankton larvae development was studied. In May, the crab larvae were found mostly in the open part of the bay. In June, they were transported by the current to the northern part of the bay. In July, they spread uniformly in all the bay areas; however, patchiness was observed. The maximal population density of the crab larvae was registered for July and varied from 6.8 to 23.3 ind. m⁻³. The crab larvae appeared in the plankton in 2000 and 2001 earlier than for the average season.     

The key features of the bottom sediment composition in the anoxic Lake Mogil’noe

In the summer 2006, integrated geological, geochemical, hydrological, and hydrochemical studies were performed on the relict anoxic Lake Mogil’noe (down to 16 m depths) located on Kil’din Island in the Barents Sea. The chemical and grain-size composition of the bottom sediments were compared for the lake (a permanently anoxic basin) and the Baltic Sea Deeps (periodically anoxic basins). The vertical location of the hydrogen sulfide layer boundary in the lake (9–11 m depths) was practically the same from 1974 up to now. The concentrations of suspended particulate matter in the lake in June and July 2006 appeared to be close to its summer concentrations in the seawaters of the open part of the Baltic Sea. The mud from Lake Mogil’noe compared to those of the Baltic Sea Deeps are characterized by fluid and flake consistency and by pronounced admixtures of sandy and silty fractions probably of eolic origin. The lacustrine mud contain much plant remains; iron sulfides and vivanite were also found in ooze. The concentrations of 22 elements determined in the lacustrine bottom sediments were of the same levels as those found here 33 years ago. The concentrations also appeared to be close to those in the corresponding grain-size types of the bottom sediments in the Baltic Sea. The low C_org/N value (5% on average) in the mud of Mogil’noe Lake compared to the values for the mud of the Baltic Sea Deeps (10% on average) points to the considerable planktogenic component in the organic matter composition of the lacustrine mud. No indications were reveled for anthropogenic contaminations of the lacustrine bottom sediments with toxic metals.     

Effects of oil exposure on pink salmon,Oncorhynchus gorbuscha,alevins in a simulated intertidal environment

Pink salmon, Oncorhynchus gorbuscha, alevins (5 and 60 days after hatching) were continuously or intermittently exposed for 30 days to the water-soluble fraction (WSF) of Cook Inlet crude oil in fresh water or in a simulated freshwater-seawater cycle. Alevins exposed to 0·7−2·4 mg/liter WSF in the simulated tidal cycle were more sensitive to oil, had reduced yolk reserves, and accumulated more hydrocarbons than did alevins exposed to the same concentrations in fresh water. Alevins in fresh water were more sensitive to continuous than to intermittent exposures. In all exposures, 60-day alevins were more severely affected than were 5-day alevins.     

三疣梭子蟹人工育苗试验初报

三疣梭子蟹 (Portunus tritubeyculatus)简称梭子蟹,是著名的大型海产食用蟹类。其肉味鲜美,营养丰富,国内外素享盛名。这种蟹子遍布我国沿海,尤以黄渤海产量最大。日本、朝鲜等国均有出产。近年来,由于捕捞强度的不断增加,世界梭子蟹资源日     

A comparative evaluation of marine sediment toxicity using bacterial luminescence,oyster embryo and amphipod sediment bioassays

The toxicity of fifty sediment samples from a heavily industrialized urban embayment (Commencement Bay, Washington) and a non-urban inlet (Carr Inlet, Washington) was measured by three bioassay techniques: Microtox (bacterial luminescence), oyster embryo and amphipod tests. In comparison with Carr Inlet sediments, twenty-nine of the Commencement Bay sediments caused a significant (P< 0·05) decrease in bacterial luminescence, seventeen caused a significant (P<0·05) increase in amphipod mortality and sixteen caused significant (P< 0·05) increase in oyster embryo abnormality. Overa ll, nineteen (41%) of the Commencement Bay sediments were either toxic in all three bioassays or non-toxic in all three bioassays.Rank-order comparisons showed a high level of agreement among the three bioassays (Kendall's coefficient of concordance = 0·64, P < 0·001). However, individual correlations suggested considerable variation among the bioassays, which may be attributable to sensitivity to individual contaminants, differences in exposure routes and the heterogeneous distribution of contaminants in Commencement Bay sediments. These results indicate the usefulness of a diversity of toxicity testing procedures in wide-scale surveys of sediment contamination. Where a high degree of concordance exists among the various bioassays, a broadly based index may be developed that encompasses a wider range of sediment toxicity than would be evident from a single testing procedure.