Effects range low and effects range median

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In environmental toxicology, effects range low (ERL) and effects range median (ERM) are measures of toxicity in marine sediment. They are used by public agencies in the United States in formulating guidelines in assessing toxicity hazards, in particular from trace metals or organic contaminants.

Contents

The ERL and ERM measures are expressed as specific chemical concentrations of a toxic substance in sediment. The ERL indicates the concentration below which toxic effects are scarcely observed or predicted: the ERM indicates that above which effects are generally or always observed. [1] They are derived from biological toxicity assays and synoptic sampling.

The numerical values are incorporated in sediment quality guidelines (SQGs) that were developed by Long and Morgan [2] for the National Oceanic and Atmospheric Administration (NOAA) National Status & Trends program as informal tools to evaluate whether a concentration of a contaminant in sediment might have toxicological effects. [3] These guidelines are used for screening sediments for trace metals and organic contaminants. [4] They are not regulatory criteria in any way and are not intended to be used as such. [3]

Derivation

NOAA originally calculated ERL/ERMs using existing toxicity data compiled from completed toxicity assays with varying endpoints, including effects on commonly tested organisms, particularly at sensitive life stages. The process is considered a "weight of evidence approach", in which results are based on a large database of previously conducted studies. The studies used included synoptically collected sediment chemical analyses and toxicity effects data. Using data already collected ("data mining") has the advantage of being able to quickly and inexpensively make an assessment with a large dataset that would otherwise require much more time-consuming and costly specific toxicity assays. Compiled data sets include a variety of endpoints including mortality, reproduction, growth rate, and juvenile survival in sediment toxicity data sets for all organisms for which tests have been conducted. Studies are screened, and only those assays using standardized methods and resulting in significant effects are used for the determination of ERL/ERM guidelines.

In summary, the key links between the compiled studies are the testing of a specific analyte - toxicity assays used are for sediment, and a significant effect must be determined. The data is arranged by ordering the concentrations from lowest to highest. After ranking, both the 10th and 50th percentile concentrations are determined over the range of endpoint concentrations. The 10th percentile of the ranked data is identified as the ERL, and is considered indicative of concentrations below which adverse effects (relatively) rarely occur. The 50th percentile of the ranked data is identified as the ERM, and is indicative of concentrations above which adverse effects (relatively) frequently occur. [1]

Government agency use

Sediment Quality Guidelines (SQGs) are used by US federal agencies, state agencies, and environmental consulting firms to characterize toxic levels of chemicals in marine and freshwater sediment. Following here is a summary of how the ERL/ERM guidelines are used by the National Oceanic and Atmospheric Administration, United States Geological Survey (USGS), and the United States Environmental Protection Agency (EPA).

NOAA

NOAA scientists use SQGs as a way to estimate if a concentration of contaminant in a sediment sample may have toxicological effects. The original intent of using SQGs was to rank order areas that may need further toxicological testing and potential chemicals of concern. Across the United States, NOAA has used these guidelines in regional surveys to determine the degree of contamination relative to other areas, and to identify if the concentration of a chemical exceeded guidelines, indicating a possible adverse effect. [3]

NOAA also reports ERLs and ERMs, along with other guidelines, on tables known as Screening Quick Reference Tables (SQuiRT) cards. These tables offer values that may be used in the preliminary screening of sediment or other media for toxic hazards. [5]

USGS

The USGS makes use of both ERL and ERM on a case-by-case basis. During a study involving the concentration of heavy metals, pesticides, and semi-volatile organic compounds in stream sediments from the Schuylkill River within the Valley Forge National Historical Park, the USGS used the ERL and ERM to determine locations that could potentially pose a threat to living organisms. [6] The USGS has also integrated ERL and ERM values into an Alert Range Table, a table that provides ranges of contaminant concentrations that predict the likelihood of adverse effects occurring in benthic organisms for the Lake Pontchartrain Basin in Louisiana. [7] Both the ERL and ERM have proven to be useful guideline values for predicting toxicity during studies conducted by the USGS.

EPA

The EPA uses ERL and ERM values as a type of sediment “benchmark”. They define a benchmark as a concentration that, when exceeded, has the potential to cause harm or significant risk to humans or animals in the environment. [4] The EPA has also used ERL and ERM values for sediment contamination studies. Assessment categories defining the condition of sampled sediments have been used by the EPA in the past. Categories have been characterized as “good” for zero ERL exceedances, “intermediate” if there are ERL exceedances but zero ERM exceedances, and “poor” for any ERM exceedance. [8] The EPA credits the ERL and ERM as valuable benchmarks that assist in providing a uniform context for evaluating contaminant levels within estuaries. [8]

Reliability

Long and colleagues, [1] using both "effects" and "no effects" data, determined measures of the accuracy of the guidelines by calculating the percent incidence of effects occurring within the ranges delineated by ERL/ERM. The percent incidence of effects was calculated by dividing the number of effects entries by the total number of entries and multiplying by 100.

For trace metals, the guidelines for copper, lead, and silver were the most accurate - below the ERL concentration, there was less than a 10% incidence of effects. A steady increase was seen between the ERL and ERM concentrations, and above the ERM, the incidence of effects was greater than 83%.

The organic contaminant guidelines also appeared to be very accurate for all classes of polycyclic aromatic hydrocarbons (PAHs) and most of the individual PAHs. The incidence of effects was 25% or below when the concentrations were below the respective ERL value, with only (fluorene as an exception, while the incidence of effects was 75% or greater at concentrations above the respective ERM, excepting dibenzo(a,h)anthracene, p,p’-DDE, total dichlorodiphenyltrichloroethane (DDT), and total Polychlorinated biphenyls (PCBs). Importantly, one hundred percent effects were seen in concentrations above the ERM for acenaphthylene, 2-methyl naphthalene, and low-molecular weight PAHs, and ninety percent or greater effects in this range were seen for chromium, lead, silver, benz(a)anthracene, and fluoranthene.

Contaminants that were reported as having low accuracies included nickel, mercury, chromium, total PCBs, p,p’-DDE, and total DDT.

Comparison to other SQGs (case studies)

Multiple case studies have been conducted to compare different sediment quality guidelines (SQGs) and their ability to predict sediment toxicity. The original intent of NOAA in developing ERL/ERMs was to create a ranking system for sediment site toxicity in order to compare one site to another. [3] [9] Although not the original intent, these guidelines have been compared to other SQGs to assess their ability to predict sediment toxicity in different organisms.

Long and co-workers also [10] conducted a meta-analysis using 1068 sediment toxicity assays to evaluate the predictive ability of the ERL/ERM, PEL (predicted effects level), and TEL (threshold effects level) sediment quality guidelines. They found that the ERL most accurately predicted no-effects toxicity in benthic organisms. Furthermore, it was shown that as the number of SQGs exceeded increased, the resulting toxicity of the sediment increased as well, providing strong evidence that SCGs are useful in predicting sediment toxicities. It was noted, however, that when chemicals existed in mixtures, the toxicity of sediments increased, possibly at concentrations lower than the ERL and TEL.

Vidal and Bay [11] showed that the ERM performed better than the AET (apparent effects threshold) and EqP (equilibrium partitioning) at predicting a non-toxic sediment concentration, and in general was more conservative in its estimates than the SQGQ1 (sediment quality guideline quotient) and MECq (moderate effects concentration). The purpose of their study was to compare common SQGs used for site assessments in California. Both of these studies suggested using multiple SQGs, and gave guidance on selecting the best method based on site characteristics and the contaminants of immediate concern.

Drawbacks to the ERL/ERM approach

ERLs and ERMs must be used with caution. Overestimating the ability of these values to signal whether or not sediment may be toxic can lead to poor decisionmaking. Certain considerations must be made, and the weaknesses of these values understood, so that ERL and ERM screening levels are used properly.

The ERL and ERM are not threshold values to determine whether toxicity will occur - they are relationships between bulk chemical concentrations and toxicity effects that are expressed along a continuum. There is no concentration above which toxicity will occur and below which toxicity will not occur. [9] This fact may be overlooked by some users of ERL/ERM's, and do so could mislead the decisionmaking process.

The derivation of ERL and ERM can also cause further misconceptions - since only effects data is used in determining an ERL/ERM, there are also overlapping concentrations where there is no co-occurrence of toxicity. [9] Concentrations that did not elicit a significant effect are left out of the calculation when determining the 10th and 50th percentile values (ERL and ERM respectively). Therefore, within the ranges delineated by the ERL and ERM values, concentrations exist that were found to not have a significant biological effect.

Many substances that are found to be very toxic do not have SQGs associated with them. The ability of an SQG to predict toxicity when other substances, without SQGs, are present, is currently unknown. [3]

Particle size also plays an important role in chemical concentrations, and this factor is ignored in calculating the ERL and ERM. When using these values for screening contaminated sediment, it is likely that the ERL will be exceeded more often when the sediment contains a larger proportion of fine-grained material. This is due to the inverse relationship between chemical concentration and particle size. [9] Due to sediment concentrations being measured on a dry weight basis, other geochemical factors of sediment that may also influence contaminant bioavailibility are not considered. [3]

Another consideration is that effects to wildlife and humans from bioaccumulation are not considered in ERL and ERM measurements. [3]

Furthermore, Vidal and Bay [11] noted that the use of ERMs when DDT is present resulted in a less accurate predictive level. The authors suggested that this provides evidence that other methods could prove more protective in cases where mixtures of organics are present.

Related Research Articles

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Environmental chemistry Scientific study of the chemical and phenomena that occur in natural places

Environmental chemistry is the scientific study of the chemical and biochemical phenomena that occur in natural places. It should not be confused with green chemistry, which seeks to reduce potential pollution at its source. It can be defined as the study of the sources, reactions, transport, effects, and fates of chemical species in the air, soil, and water environments; and the effect of human activity and biological activity on these. Environmental chemistry is an interdisciplinary science that includes atmospheric, aquatic and soil chemistry, as well as heavily relying on analytical chemistry and being related to environmental and other areas of science.

Aquatic toxicology

Aquatic toxicology is the study of the effects of manufactured chemicals and other anthropogenic and natural materials and activities on aquatic organisms at various levels of organization, from subcellular through individual organisms to communities and ecosystems. Aquatic toxicology is a multidisciplinary field which integrates toxicology, aquatic ecology and aquatic chemistry.

Soil contamination Pollution of land by human-made chemicals or other alteration

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Toxicology testing Testing conducted to determine the degree to which a substance can damage a living or non-living organisms

Toxicology testing, also known as safety assessment, or toxicity testing, is the process of determining the degree to which a substance of interest negatively impacts the normal biological functions of an organism, given a certain exposure duration, route of exposure, and substance concentration. Toxicology testing is often conducted by researchers who follow established toxicology test protocol for a certain substance, mode of exposure, exposure environment, duration of exposure, or for a particular organism of interest, or for a particular developmental stage of interest. Toxicology testing is commonly conducted during preclinical development for a substance intended for human exposure. Stages of in silico, in vitro and in vivo research are conducted to determine safe exposure doses in model organisms. If necessary, the next phase of research involves human toxicology testing during a first-in-man study. Toxicology testing may be conducted by the pharmaceutical industry, biotechnology companies, contract research organizations, or environmental scientists.

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The Biotic Ligand Model (BLM) is a tool used in aquatic toxicology that examines the bioavailability of metals in the aquatic environment and the affinity of these metals to accumulate on gill surfaces of organisms. BLM depends on the site-specific water quality including such parameters as pH, hardness, and dissolved organic carbon. In this model, lethal accumulation values are used to be predictive of lethal concentration values that are more universal for aquatic toxicology and the development of standards. Collection of water chemistry parameters for a given site, incorporation of the data into the BLM computer model and analysis of the output data is used to accomplish BLM analysis. Comparison of these values derived from the model, have repeatedly been found to be comparable to the results of lethal tissue concentrations from acute toxicity tests. The BLM was developed from the gill surface interaction model (GSIM) and the free ion activity model (FIAM). Both of these models also address how metals interact with organisms and aquatic environments. Currently, the United States Environmental Protection Agency (EPA) uses the BLM as a tool to outline Ambient Water Quality Criteria (AWQC) for surface water. Because BLM is so useful for investigation of metals in surface water, there are developmental plans to expand BLM for use in marine and estuarine environments.

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An early life stage (ELS) test is a chronic toxicity test using sensitive early life stages like embryos or larvae to predict the effects of toxicants on organisms. ELS tests were developed to be quicker and more cost-efficient than full life-cycle tests, taking on average 1–5 months to complete compared to 6–12 months for a life-cycle test. They are commonly used in aquatic toxicology, particularly with fish. Growth and survival are the typically measured endpoints, for which a Maximum Acceptable Toxicant Concentration (MATC) can be estimated. ELS tests allow for the testing of fish species that otherwise could not be studied due to length of life, spawning requirements, or size. ELS tests are used as part of environmental risk assessments by regulatory agencies including the U.S. Environmental Protection Agency (EPA) and Environment Canada, as well as the Organisation for Economic Co-operation and Development (OECD).

Simultaneously extracted metals/Acid-volatile sulfide (SEM-AVS) is an approach used in the field of aquatic toxicology to assess the potential for metal ions found in sediment to cause toxic effects in organisms dwelling in the sediment. In this approach, the amounts of several heavy metals in a sediment sample are measured in a laboratory; at the same time, the amount of acid-volatile sulfide is determined. Based on the chemical interactions between heavy metals (SEM) and acid-volatile sulfide (AVS), the concentrations of these two components can be used to assess the potential for toxicity to sediment-dwelling organisms.

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Equilibrium partitioning Sediment Benchmarks (ESBs) are a type of Sediment Quality Guideline (SQG) derived by the US Environmental Protection Agency (EPA) for the protection of benthic organisms. ESBs are based on the bioavailable concentration of contaminants in sediments rather than the dry-weight concentration. It has been demonstrated that sediment concentrations on a dry-weight basis often do not predict biological effects. Interstitial water concentrations, however, predict biological effects much better. This is true because the chemical present in the interstitial water is the uncomplexed/free phase of the chemical that is bioavailable and toxic to benthic organisms. Other phases of the chemical are bound to sediment particles like organic carbon (OC) or acid volatile sulfides (AVS) and are not bioavailable. Thus the interstitial water concentration is important to consider for effects to benthic organisms.

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In aquatic toxicology, the sediment quality triad (SQT) approach has been used as an assessment tool to evaluate the extent of sediment degradation resulting from contaminants released due to human activity present in aquatic environments. This evaluation focuses on three main components: 1.) sediment chemistry, 2.) sediment toxicity tests using aquatic organisms, and 3.) the field effects on the benthic organisms. Often used in risk assessment, the combination of three lines of evidence can lead to a comprehensive understanding of the possible effects to the aquatic community. Although the SQT approach does not provide a cause-and-effect relationship linking concentrations of individual chemicals to adverse biological effects, it does provide an assessment of sediment quality commonly used to explain sediment characteristics quantitatively. The information provided by each portion of the SQT is unique and complementary, and the combination of these portions is necessary because no single characteristic provides comprehensive information regarding a specific site

Toxicological databases are large compilations of data derived from aquatic and environmental toxicity studies. Data is aggregated from a large number of individual studies in which toxic effects upon aquatic and terrestrial organisms have been determined for different chemicals. These databases are then used by toxicologists, chemists, regulatory agencies and scientists to investigate and predict the likelihood that an organic or inorganic chemical will cause an adverse effect on exposed organisms.

SPMDs, or semipermeable membrane devices, are a passive sampling device used to monitor trace levels of organic compounds with a log Kow > 3. SPMDs are an effective way of monitoring the concentrations of chemicals from anthropogenic runoff and pollution in the marine environment because of their ability to detect minuscule levels of chemical. The data collected from a passive sampler is important for examining the amount of chemical in the environment and can therefore be used to formulate other scientific research about the effects of those chemicals on the organisms as well as the environment. Examples of commonly measured chemicals using SPMDs include: PAHs, PCBs, PBDEs, dioxins and furans as well as hydrophobic waste-water effluents like fragrances, triclosan and phthalates.

Toxic units (TU) are used in the field of toxicology to quantify the interactions of toxicants in binary mixtures of chemicals. A toxic unit for a given compound is based on the concentration at which there is a 50% effect for a certain biological endpoint. One toxic unit is equal to the EC50 for a given endpoint for a specific biological effect over a given amount of time. Toxic units allow for the comparison of the individual toxicities of a binary mixture to the combined toxicity. This allows researchers to categorize mixtures as additive, synergistic or antagonistic. Synergism and antagonism are defined by mixtures that are more or less toxic than predicted by the sum of their toxic units.

References

  1. 1 2 3 Long, Edward R., Donald D. McDonald, Sherri L. Smith, and Fred D. Calder. "Incidence of Adverse Biological Effects Within Range of Chemical Concentrations in Marine and Estuarine Sediments." Environmental Management 19.1 (1995): 81-97.
  2. ↑ Long E.R., L.G. Morgan. "The Potential for Biological Effects of Sediment-Sorbed Contaminants Tested in the National Status and Trends Program". NOAA Technical Memorandum NOS OMA 52. National Oceanic and Atmospheric Administration. Seattle, Washington. 1990.
  3. 1 2 3 4 5 6 7 "Sediment Quality Guidelines Developed for the National Status and Trends Program" Archived 2013-06-12 at the Wayback Machine . NOAA. 1999. Accessed: June 4, 2012.
  4. 1 2 "Sediment Benchmarks for Aquatic Life". EPA. 2011. Accessed: May 3, 2012.
  5. ↑ Buchman, M. F. NOAA Quick Screening Reference Tables. NOAA OR&R Report 08-1 Seattle WA, Office of Response and Restoration Division, National Atmospheric and Oceanic Administration (2008): 34 pages.
  6. ↑ Reif, A., Sloto, R. Metals, Pesticides, and Semi-Volatile Organic Compounds in Sediment in Valley Forge National Historic Park, Montgomery County, Pennsylvania. United States Geological Survey. Water Resources Investigations Report (1997): 97-4120.
  7. ↑ United States Geological Survey. 2002. Lake Pontchartrain Basin: Bottom Sediments and Related Environmental Resources. http://pubs.usgs.gov/pp/p1634j/html/fm_range.htm. Accessed June 4, 2012.
  8. 1 2 EPA. 2012. Sediment Contamination. http://www.epa.gov/emap/maia/html/docs/Est5.pdf Accessed: May 24, 2012.
  9. 1 2 3 4 O’Connor, Thomas P. "The Sediment Quality Guideline, ERL, Is Not a Chemical Concentration at the Threshold of Sediment Toxicity." Marine Pollution Bulletin 49.5-6 (2004): 383-85.
  10. ↑ Long, Edward R., L. Jay Field, and Donald D. MacDonald. "Predicting Toxicity In Marine Sediments With Numerical Sediment Quality Guidelines." Environmental Toxicology and Chemistry 17.4 (1998): 714.
  11. 1 2 Vidal, Doris E., and Steven M. Bay. "Comparative Sediment Quality Guideline Performance For Predicting Sediment Toxicity In Southern California, USA." Environmental Toxicology and Chemistry 24.12 (2005): 3173.
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