Jerry M. Neff

Ecological risk assessment of polycyclic aromatic hydrocarbons in sediments: Identifying sources and ecological hazard

Abstract Polycyclic aromatic hydrocarbons (PAHs) are nearly ubiquitous contaminants of freshwater and marine sediments. Sediment PAHs are derived from combustion of organic matter, fossil fuels, and biosynthesis by microbes. Pyrogenic PAHs, particularly those associated with combustion particles (soot), have a low accessibility and bioavailability in sediments. Polycyclic aromatic hydrocarbons associated with petroleum, creosote, or coal tar in sediments may have a moderate accessibility/bioavailability, particularly if the PAHs are part of a nonaqueous phase liquid (NAPL) phase that is in contact with sediment pore water. We present a method for estimating the hazard of complex PAH assemblage in sediments to benthic organisms. Concentrations of all PAHs in sediment pore water are estimated by an equilibrium partitioning model relative to concentrations in bulk sediment. Predicted log Koc values can be used for predicting sediment/water partitioning of petrogenic PAH, but empirically derived log Kd values are needed to predict partitioning of pyrogenic PAH. A hazard quotient (HQ) for each PAH is calculated as the ratio of the estimated concentration in pore water to the chronic toxicity of the PAH determined by a log Kow/toxicity model. Hazard quotients for all PAH in a sample are summed to produce a hazard index (HI), which is a measure of the worst-case estimated hazard of the sediment PAH to benthic organisms. The results of this study show that the integration of HI results with PAH source data provides insights into the causes of sediment toxicity that are useful in an ecological risk assessment.

Quantitative semi-automated enzymatic assay for tissue glycogen

A simple, rapid, specific and reproducible assay for tissue glycogen is described. The method involves the incubation of a denatured tissue homogenate with amyloglucosidase resulting in the complete hydrolysis of glycogen to glucose. The glucose content of the homogenate supernatant is then determined with the aid of a glucose analyzer. The method has been used to measure the glycogen content of a variety of discrete and complex animal tissues and is particularly convenient for microdeterminations.

Species sensitivity distributions for suspended clays, sediment burial, and grain size change in the marine environment

Assessment of the environmental risk of discharges, containing both chemicals and suspended solids (e.g., drilling discharges to the marine environment), requires an evaluation of the effects of both toxic and nontoxic pollutants. To date, a structured evaluation scheme that can be used for prognostic risk assessments for nontoxic stress is lacking. In the present study we challenge this lack of information by the development of marine species sensitivity distributions (SSDs) for three nontoxic stressors: suspended clays, burial by sediment, and change in sediment grain size. Through a literature study, effect levels were obtained for suspended clays, as well as for burial of biota. Information on the species preference range for median grain size was used to assess the sensitivity of marine species to changes in grain size. The 50% hazardous concentrations (HC50) for suspended barite and bentonite based on 50% effect concentrations (EC50s) were 3,010 and 1,830 mg/L, respectively. For burial the 50% hazardous level (HL50) was 5.4 cm. For change in median grain size, two SSDs were constructed; one for reducing and one for increasing the median grain size. The HL50 for reducing the median grain size was 17.8 mum. For increasing the median grain size this value was 305 mum. The SSDs have been constructed by using information related to offshore oil- and gas-related activities. Nevertheless, the results of the present study may have broader implications. The hypothesis of the present study is that the SSD methodology developed for the evaluation of toxic stress can also be applied to evaluate nontoxic stressors, facilitating the incorporation of nontoxic stressors in prognostic risk assessment tools.

Impacts of exploratory drilling for oil and gas on the benthic environment of Georges Bank

Abstract A 3-year monitoring program was performed to assess the impacts of exploratory drilling for oil and gas on the benthic environment of Georges Bank, an important commercial fishery region in the North Atlantic east of Massachusetts, USA. Surficial sediments were sampled for chemical and benthic infaunal analysis and bottom still photographs were taken to document bottom microtopography and epifauna at 46 stations during 12 field surveys. The surveys were performed quarterly from just before drilling began, during drilling, and for nearly 2 years after completion of drilling. Two of the eight drilling sites were selected for monitoring. Twenty-nine stations were positioned in a tight radial array around a drilling site in 80 m of water. A second group of three stations was positioned near another drilling site in 140 m of water. The remaining stations covered a broad expanse of the Bank and adjacent suspected sites of deposition of fine-grained sediments. Of the 12 elements analyzed in bulk sediments, only barium increased in concentration during the period when drilling was taking place (July 1981 to September 1982). The concentration of barium in surficial sediment increased 4·7-fold from 28 ppm before drilling to 131·7 ppm after drilling at the station closest to the drilling site in 80 m of water and 5·9-fold from 32 ppm before drilling to 172 ppm after drilling at the station closest to the drilling site in 140 m of water. The concentrations of both barium and chromium increased in the fine (silt/clay) fraction (usually less than 5% by weight of sediment from most stations) of sediments from several stations around one or both rig sites monitored during the period of drilling. Elevated concentrations of chromium (about two-fold) occurred only in sediments near the drilling site in 140 m of water. Statistically significant increases in the concentration of barium in the fine fraction to sediment were detected approximately 65 km west (downcurrent) and 35 km east of the drilling site in 80 m of water after drilling was completed. The benthic fauna were abundant and diverse throughout the study area. At most stations, the dominant species remained nearly the same from one season to another over the 3 years of sampling. Polychaetes were the most abundant, followed by crustaceans. The number of individuals of some species, particularly the amphipods Erichthonius fasciatus and Unciola inermis , showed large seasonal variations. Cluster analysis revealed a strong relationship between community structure and both sediment type and water depth. Little seasonal variation was detected, but some interannual differences were revealed by cluster analysis and correspondence analysis. The replicates from a station always resembled each other more than they resembled any replicates from other stations. In addition, the combined replicates from a station always clustered with samples from that station taken on other cruises. This excellent replication and uniformity of the benthic infaunal community at a station over time made it possible to detect very subtle changes in community parameters that might be related to discharges of drilling fluid and drill cuttings. Nevertheless, no changes were detected in benthic communities of Georges Bank that could be attributed to drilling activities.

Bioaccumulation of organic micropollutants from sediments and suspended particulates by aquatic animals

ZusammenfassungNicht-polare organische Verunreinigungen, wie polycyclische aromatische Kohlenwasserstoffe, polychlorierte Biphenyle und einige Pesticide, die an Sedimente adsorbiert sind, besitzen eine niedrige Bioverfügbarkeit für Süßwasser- und Seetiere. Die Bioakkumulationsfaktoren aus den Sedimenten (Konzentration im Tier/Konzentration im Sediment) reichen für die untersuchten Verunreinigungen von weniger als 0,1 bis etwa 20, d.h. mehrere Größenordnungen kleiner als die entsprechenden Faktoren aus Wasser. Die Bioverfügbarkeit der an Sediment adsorbierten Verunreinigungen steht im direkten Verhältnis zu der Löslichkeit der Betreffenden Verbindung und der Korngröße des Sediments, und ist umgekehrt proportional zu der Konzentration an organischem Kohlenstoff im Sediment und der Größe des Tieres. Die an Sediment adsorbierten Verunreinigungen sind nur gering bioverfügbar, die Sedimente in kontaminierten Gebieten enthalten aber oft hohe Konzentrationen an Verunreinigungen. Daher stellen die Sedimente eine bedeutende Verunreinigungsquelle für Süßwasser- und Meerestiere dar.SummaryNon-polar organic micropollutants, such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls and some pesticides, which are adsorbed to sediments have a low bioavailability to freshwater and marine animals. Bioaccumulation factors from sediments (concentration in animal/concentration in sediment) of the organic pollutants investigated range from less than 0.1 to about 20, several orders of magnitude lower than bioaccumulation factors from the water for the same compounds. Bioavailability of sediment-adsorbed organic micropollutants is directly related to the solubility of the compound and sediment grain size, and inversely related to sediment organic carbon concentration and animal size. Organic micropollutants adsorbed to sediments are only slightly bioavailable, but sediments in contaminated areas often contain high concentrations of adsorbed pollutants; therefore they represent an important source of contamination of freshwater and marine animals.

Polycyclic aromatic hydrocarbon levels in mussels from prince william sound, ALASKA, USA, document the return to baseline conditions

Bioavailable hydrocarbons in the Exxon Valdez oil spill zone in Prince William Sound (PWS; AK, USA) shorelines were at or near background levels in 2002, as indicated by low concentrations of polycyclic aromatic hydrocarbons (PAHs) in mussels (Mytilus trossulus) collected from sites throughout PWS. Total PAH (TPAH) minus parent naphthalene concentrations in mussels collected in 1998 to 2002 from sites oiled in 1989 were at or near reference-site values. Both oiled and reference sites included locations associated with past human and industrial activity (HA). Inclusion of the unoiled HA sites in the range of reference sites that define prespill conditions is consistent with federal regulations. For the period from 1998 to 2002, the geometric mean of TPAH concentrations for 218 mussel samples collected from 72 sites, including four HA sites that had been heavily oiled in 1989, is 54 ng/g dry weight (range, 2-1,190 ng/g). The maximum mussel TPAH concentrations are equivalent to a weathered-oil exposure dose to intertidal foragers that is one to three orders of magnitude less than the doses shown to cause sublethal effects in surrogate species. The geometric mean of TPAH concentrations for mussel samples from 28 locations not oiled in 1989 and unaffected by human use (NHA sites) is 28 ng/g (range, 3-355 ng/g), whereas the geometric mean of TPAH concentrations for mussel samples from 14 locations not oiled in 1989 and affected by human use (HA sites) is 106 ng/g (range, 2-12,056 ng/g). The range of data for the unoiled HA and NHA sites defines the background of bioavailable PAHs to mussels on western PWS shorelines that would have prevailed if the oil spill had not occurred. The low PAH concentrations in mussels from sites known to have subsurface oil residues demonstrates the low bioavailability of these spill remnants and, thus, are a low additional risk to foraging wildlife. The present study shows continuous exposure from four- to six-ring PAHs originating at HA sites in western PWS. At low concentrations, these PAHs are known to cause adverse biological effects. However, in the context of PWS, oiled and HA sites represent a small percentage (approximately 0.1-0.2%) of the total PWS shoreline.

Bioavailability of polycyclic aromatic hydrocarbons from buried shoreline oil residues thirteen years after the Exxon Valdez oil spill: A multispecies assessment

Seven taxa of intertidal plants and animals were sampled at 17 shoreline sites in Prince William Sound ([PWS]; AK, USA), that were heavily oiled in 1989 by the Exxon Valdez oil spill (EVOS) to determine if polycyclic aromatic hydrocarbons (PAH) from buried oil in intertidal sediments are sufficiently bioavailable to intertidal prey organisms that they might pose a health risk to populations of birds and wildlife that forage on the shore. Buried residues of EVOS oil are present in upper and middle intertidal sediments at 16 sites. Lower intertidal (0 m) sediments contain little oil. Much of the PAH in lower intertidal sediments are from combustion sources. Mean tissue total PAH (TPAH) concentrations in intertidal clams, mussels, and worms from oiled sites range from 24 to 36 ng/g (parts per billion) dry weight; sea lettuce, whelks, hermit crabs, and intertidal fish contain lower concentrations. Concentrations of TPAH are similar or slightly lower in biota from unoiled reference sites. The low EVOS PAH concentrations detected in intertidal biota at oiled shoreline sites indicate that the PAH from EVOS oil buried in intertidal sediments at these sites have a low bioavailability to intertidal plants and animals. Individual sea otters or shorebirds that consumed a diet of intertidal clams and mussels exclusively from the 17 oiled shores in 2002 were at low risk of significant health problems. The low concentrations of EVOS PAH found in some intertidal organisms at some oiled shoreline sites in PWS do not represent a health risk to populations of marine birds and mammals that forage in the intertidal zone.

Chapter 14 – Monocyclic Aromatic Hydrocarbons in the Ocean

Publisher Summary A large number of monocyclic aromatic hydrocarbons, benzene, and its alkyl homologs, are present in crude and refined petroleum products. Some are natural products, synthesized by many bacteria, fungi, plants, and animals. A significant percentage of some crude oils comprises monocyclic aromatic hydrocarbons. Automotive gasoline, a low-boiling distillate of crude oil, typically contains 12 to more than 50% total monocyclic aromatic hydrocarbons. The mono-aromatic hydrocarbons of greatest concern in the environment are benzene, toluene, ethylbenzene, and m-, p-, and o-xylenes (BTEX). BTEX are low molecular weight mono-aromatic hydrocarbons that are moderately soluble in fresh water and seawater and are highly volatile. Solubility in seawater is lower than that in fresh water because of salting out. Because of their chemical/physical properties, BTEX are not persistent in seawater, bind only weakly to marine sediments, and are not bioaccumulated to high concentrations by marine organisms. BTEX reaches the marine environment in domestic and industrial waste water effluents, runoff from land, and spills of crude and refined petroleum products. Other sources may be locally important. Although the amounts entering the marine environment are undoubtedly very large, concentrations of BTEX in seawater and estuarine waters generally are very low.

Toxicity of weathered Exxon Valdez crude oil to pink salmon embryos

Research was conducted at the University of Idaho (Moscow, ID, USA) on the toxicity of weathered Exxon Valdez crude oil to embryos of pink salmon from 2001 to 2003 for the purpose of comparing these data with those from the National Oceanic and Atmospheric Administration Fisheries Laboratory at Auke Bay (AK, USA). Mortality reported at Auke Bay for embryos chronically exposed to very low concentrations of aqueous solutions of weathered oil, measured as dissolved polycyclic aromatic hydrocarbons (PAHs), was inconsistent with that in other published research. Using the Auke Bay experimental design, we found that toxicity is not evident in pink salmon embryos until chronic exposure to laboratory weathered and naturally weathered oil concentrations exceeding 1,500 and 2,250 ppm, respectively, representing a total PAH tissue burden in excess of 7,100 ppb. Effluent hydrocarbons also drop well below concentrations sufficient to cause harm over the time frame of a few weeks, regardless of oiling level. Resolution of differences with Auke Bay involved the source of contributing hydrocarbons. The experimental design did not exclude dispersed oil droplets from the aqueous solution; thus, toxicity was not limited to the dissolved hydrocarbon fraction. The implications of the present results are discussed regarding the toxic risk of weathered oil to pink salmon embryos in streams of Prince William Sound (AK, USA).

Evaluating the aquatic toxicity of complex organic chemical mixtures: Lessons learned from polycyclic aromatic hydrocarbon and petroleum hydrocarbon case studies

Experimental designs for evaluating complex mixture toxicity in aquatic environments can be highly variable and, if not appropriate, can produce and have produced data that are difficult or impossible to interpret accurately. We build on and synthesize recent critical reviews of mixture toxicity using lessons learned from 4 case studies, ranging from binary to more complex mixtures of primarily polycyclic aromatic hydrocarbons and petroleum hydrocarbons, to provide guidance for evaluating the aquatic toxicity of complex mixtures of organic chemicals. Two fundamental requirements include establishing a dose-response relationship and determining the causative agent (or agents) of any observed toxicity. Meeting these 2 requirements involves ensuring appropriate exposure conditions and measurement endpoints, considering modifying factors (e.g., test conditions, test organism life stages and feeding behavior, chemical transformations, mixture dilutions, sorbing phases), and correctly interpreting dose-response relationships. Specific recommendations are provided.