API PUBL 4751-2005 pdf free download

API PUBL 4751-2005 pdf free download.Evaluation of Water Quality Translators for Mercury.
This report presents an overview and discussion of the use of the ambient water quality criterion for methylmercury developed by the U.S. Environmental Protection Agency (EPA) in 2001 (66 FR 1344). Unlike all other previous water quality criteria for the protection of human health, the criterion for methylmercury was issued as a fish tissue concentration (i.e., 0.3 mg methylmercury/Kg wet weight fish tissue), as the fish consumption pathway is the main route of exposure to mercury in the environment. As a result, enforcement of water quality standards based upon this criterion requires either fish tissue sampling or the conversion of the criterion to a concentration in water, especially for the development of National Pollutant Discharge Elimination System (NPDES) permits. Because many permitted dischargers will be faced with meeting the methylmercury criterion, this report focuses on (1) available analytical methods for evaluating mercury in fish and water;; (2) the proposed methods for translating a fish tissue concentration for mercury into a concentration in water; and (3) implementation of the mercury criterion in the development of Total Maximum Daily Loads (TMDLs) and water quality-based effluent limits (WQBELs). EPA (2002a, 2004a) draft Guidance for Implementing the January 2001 Methylmercury Water Quality Criterion addresses these issues and is discussed below in each relevant section. Issues regarding mercury are significant because of mercury’s complex cycling in the environment, high bioaccumulative potential, and high toxicity. Generally, inorganic mercury is deposited to water bodies through atmospheric deposition (the major pathway), runoff, stormwater discharge, or other industrial or municipal discharges. Once in the water body, mercury deposited in sediments or dissolved in water may be methylated by bacteria to form methylmercury. Methylmercury is highly bioaccumulative and is the form of mercury that is accumulated up the food web. EPA’s criterion for methylmercury assumes, t
2 Analytical Methods Analytical methods to quantify different species of mercury in environmental samples continue to be refined. Section 2 discusses the various methods available for evaluating the forms of mercury in fish tissue and water and reviews factors to consider in selecting an appropriate analytical method. 2.1 METHODS FOR EVALUATING TOTAL MERCURY IN FISH TISSUE AND WATER For measuring total mercury, EPA Method 1631 can be used on water samples, while EPA Method 747B/SW-846 can be used for solid or semi-solid samples. A brief description of each method, its detection limits, precision, accuracy, and costs is provided below. 2.1.1 Method 1631 EPA Method 1631 can be used for the determination of total mercury in filtered and unfiltered water (EPA 2002b). Method 1631 is carried out in several steps. First, the various mercury species are oxidized to Hg(II) with bromine monochloride (BrCl). Second, the mercury is reduced to elemental mercury (Hg(0)) with hydroxylamine hydrochloride (NH 2 OH·HCl) and stannous chloride (SnCl 2 ). Third, mercury is purged from the sample onto gold traps for pre-concentration. The gold traps are heated to release the elemental mercury and the detection is performed with cold-vapor atomic fluorescence spectroscopy (CVAFS). Method 1631 has a method detection limit of 0.2 ng/L. This is a performance-based method and actual criteria data are determined before and during analysis. Precision is based on replicate analysis of actual samples and has a limit of 21% RSD (relative standard deviation). Accuracy is determined using National Institute of Standards and Technology (NIST) standards for ongoing precision and recovery (OPR) and matrix spikes/matrix spike duplicates (MS/MSD). OPR samples must fall within 77 – 123% and MS/MSD samples between 71 – 125%. Many laboratories perform this analysis; costs range from $55 – 200 per sample with a four week reporting time. 2.1.2 Method 7471B/SW-846 EPA Method 7471B/SW-846 is designed for solid or semi-solid samples, but may also be used for water or aqueous samples, as the analysis portion of this method is covered by EPA Method 245.5 (EPA 1994a). Using this method, solid or liquid samples are digested using a potassium permanganate and acid digestion. The acid digestion ensures that all forms of mercury are oxidized to a water soluble Hg(II) form. The detection is performed using cold-vapor atomic adsorption spectroscopy (CVAAS). In CVAAS the sample is reacted with stannous chloride and the mercury is converted to elemental mercury. The elemental mercury is purged from the sample with nitrogen to an atomic adsorption detector. Typical method detection limits for mercury using this method are 0.2 µg/L. This is a performance based method and actual criteria data are determined before and during analysis. Precision is based on replicate analysis of actual samples although no limits were set in the method. Accuracy is determined using NIST standards for ongoing precision and recovery (OPR) and matrix spikes and matrix spike duplicates (MS/MSD). OPR samples must fall within 90 – 110% and MS/MSD samples between 85 – 115%. Many laboratories perform this analysis and the costs range from $51 – 200 per sample with a four week reporting time.