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.
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
Derivation
NOAA originally calculated ERL/ERMs using existing toxicity data compiled from completed toxicity
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
NOAA
NOAA scientists use SQGs as a way to estimate if a concentration of contaminant in a sediment sample may have
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,
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.
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
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.
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.
References
- ^ a b c 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.
- ^ 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.
- ^ a b c d e f g "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.
- ^ a b "Sediment Benchmarks for Aquatic Life". EPA. 2011. Accessed: May 3, 2012.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ a b EPA. 2012. Sediment Contamination. http://www.epa.gov/emap/maia/html/docs/Est5.pdf Accessed: May 24, 2012.
- ^ a b c d 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.
- ^ 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.
- ^ a b 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.