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Method for Rapid Detection of Heavy Metal Contamination in Fish Species from Lake Tuskegee using Inductively Coupled Plasma-Mass Spectroscopy

Wilson, Thomas
Alabama A&M University
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The goals of this project are to use inductively coupled plasma -Mass Spectroscopy (ICP-MS) available in the School of Agricultural and Environmental Sciences (SAES) to develop a rapid detection methodology for the quantification of trace metals including mercury, cadmium, arsenic and other heavy metal contaminants. ICP-MS is not recognized as the standard method for the detection of methyl and di-methyl mercury however, as a part of this study, I propose to attempt to develop ICP-MS as a methodology for mercury detection.

A second objective of this project will be to develop a Risk Assessment of the potential for adverse health effects due to heavy metal ingestion from fish species in Lake Tuskegee based upon the quantification of levels of heavy metals which pass through processing to the consumer. Considering that fish products have been recognized as a particularly important source of the overall metals exposure, undertaking a risk assessment appears to be justified. Risk assessment, as a part of risk analysis, is defined as the process of evaluating the possibility of adverse health effects that may occur as a consequence of exposure to a hazard. This scientifically based process consists of hazard identification, hazard characterization, exposure assessment, and risk characterization (fig 1). At the beginning of the risk assessment process, the sources and types of a potential hazard should be considered and the ensuing appropriate monitoring by processors should be established. For this purpose, various factors, such as: the threshold amount of toxic contaminants the relationship between the exposure level and frequency of adverse health effects (dose-response assessment), the severity of the health effects, by considering multiple biological endpoints (for example, morbidity, fatalities), which have an effect on the health threat, should be taken into consideration. Finally, it is important to emphasize the qualitative description and quantitative evaluation of heavy metal contamination of fish species present in Lake Tuskegee which is utilized both as a source for municipal drinking water, and for recreational fishing.

Specific research objectives are to:

  1. Develop a rapid method for the detection of heavy metal contaminants including mercury using ICP-MS
  2. Use results to perform a Risk Assessment to assess the risk of dietary intake of heavy metal analytes from fish products originating in Tuskegee Lake.
More information
Non-Technical Summary: The seafood industry is a multi-billion dollar industry in the United with retail sales of over $25 billion annually. Consumption is expected to increase as people continue to look for more safe and healthy food choices. Fresh, frozen and ready-to-eat fish products are the largest growth areas. Of particular interest and concern is the ingestion of heavy metal contaminants through the consumption of commercially available or recreationally captured fish that may be contaminated. Recent concerns over the safety of imported seafood products, and pressure from environmental groups to examine the safety of fish products in the US diet makes this an important issue. Because of the wide range of products in the marketplace, reliance on old data make safety assessments based upon it unreliable. An additional concern is that many of the studies, particularly those conducted by the EPA including the controversial 192-1996 study of fish contamination in the Columbia River (Hanford Reach) sampled and tested only a few fish and more importantly, tested whole fish or only certain tissues, not the edible portion as consumed. The Hite studies of 2002 and 2003 have similar critical flaws including the fact that very few fish were examined, and many of these were purchased at retail, with no indication of what the actual harvest area may have been. Heavy metals are regarded as toxic to living organisms because of their tendency to accumulate in selected tissues. These elements are introduced into the environment through various routes, smelting processes, fuel combustion and industrialization. They make their way into aquatic systems, rivers, lakes or oceans through atmospheric fallout, dumping wastes, accidental leaks, runoff of terrestrial systems (industrial and domestic effluents) and geological weathering, agricultural chemical use and urban activities of human beings. These agents have led to metal dispersion in the environment and, consequently, impaired health of the population by the ingestion of fish products contaminated by harmful elements. Exposures of humans to environmental chemicals can occur simultaneously from various sources. Lake Tuskegee is a freshwater man-made Lake owned by the city of Tuskegee and it is located within residential areas in Tuskegee, Alabama. Its latitude and longitude coordinates are 32.42166 and ?85.67777 respectively. The Lake is a 92-acre body of water that is fed by several large springs. It is separated into 2 smaller Lakes by a 1,000 ft long dam that has a maximum height of 23 ft. The Lake has a 17 ft deep key in the center to prevent seepage. In order to provide adequate strength for flood conditions, the base of the dam is 100 ft wide (Tuskegee News, 1948). A sewer line on concrete pillars over one neck of the Lake was extended into the stream below the dam and septic tanks on the surrounding hillsides were altered to prevent water contamination. After the development of the Lake, it was stocked with about 3,000 bream, bass and speckled catfish. The Lake also provides a source of additional fish protein to some inhabitants of the area.

Approach: Samples will be collected according to the method of Ikem and Egiebor wherein three samples of largemouth bass (Micropterus salmoides), the most common type of fish in Lake Tuskegee and widely consumed will be caught with fishing rods using artificial bass bates. For comparison and control purposes, another three largemouth bass (Micropterus salmoides) and three striped bass (Morone saxatilis) samples will be purchased from commercial sources such as a farmers market. All fish samples obtained will be kept on ice in the field and transported to the laboratory in Huntsville or Tuskegee (with cooperation and approval of the collaborators at Tuskegee University). The fish samples will be weighed, measured and frozen until ready for acid digestion. Prior to digestion, the fish samples will be thawed. Known weights (wet weight) of fish muscle, vertebral column, gills, and liver samples will be digested in nitric acid and subjected to microwave program as follows: Step 1: 25-96 ?C for 20 min at 1000 W; Step 2: hold at 96 ?C for 30 min; Step 3: 180 ?C for 10 min at 1000 W; hold at 180 ?C for 10 min then cooled to room temperature after which, 2 ml of 30% hydrogen peroxide will be added to each digest in the vessel and the mixture was again subjected to Step 3 above. Digests will be made up to 25 ml in acid washed standard flasks and then placed in acid washed 60 ml polyethylene bottles. The levels of selected heavy metals including but not limited to Cr, Cd, Cu, Fe, Pb, in digests will be determined using ICP-MS. To check the accuracy of the methodology used for fish, bovine liver (SRM 1577b) from NIST will passed through the same analytical process used for the fish samples. As a further control, method blanks will also be conducted for all metal determinations in fish. ICP-MS: Inductively coupled plasma mass spectrometry (ICP-MS) is a type of mass spectrometry that is highly sensitive and capable of the determination of a range of metals and several non-metals at concentrations below one part in 1012 . It is based on coupling together inductively coupled plasma as a method of producing ions (ionization) with a mass spectrometer as a method of separating and detecting the ions. ICP technology was built upon the same principles used in atomic emission spectrometry. Samples are decomposed to neutral elements in high temperature argon plasma and analyzed based on their mass to charge ratios. An ICP-MS can be thought of as four main processes, including sample introduction and aerosol generation, ionization by an argon plasma source, mass discrimination, and the detection system. The schematic below illustrates this sequence of processes One of the great advantages to ICP-MS is extremely low detection limits for a wide variety of elements. Some elements can be measured down to part per quadrillion ranges while most can be detected at part per trillion levels. The table below shows some common ICP-MS detection limits by element. Element Detection Limit (ppt) U, Cs, Bi less than 10 Ag, Be, Cd, Rb, Sn, Sb, Au 10-50 Ba, Pb, Se, Sr, Co, W, Mo, Mg 50-100 Cr, Cu, Mn 100-200 Zn, As, Ti 400-500 Li, P 1-3 ppb Ca less than 20 ppb

Funding Source
Nat'l. Inst. of Food and Agriculture
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Risk Assessment, Management, and Communication
Chemical Contaminants
Natural Toxins
Sanitation and Quality Standards