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Trace Metals Unit - Fish Testing
Information on Fish Testing
The presence of persistent toxic substances (PTS) in aquatic ecosystems is one of the most important environmental policy issues currently facing the Great Lakes States. Contaminated fish are the primary source of chemical exposure to most humans and thus are the cause of fish consumption advisories. The MDHHS works in conjunction with the Department of Environmental Quality (DEQ) on the Michigan Fish Contaminant Monitoring Program (FCMP) to assess the chemical contamination in fish from the state's surface waters. The data generated is used to determine whether fish from waters of the state are safe for human and wildlife consumption, and as a surrogate measure of bioacumulative contaminants in surface water.
The Trace Metals Unit tests homogenized fish tissue samples for mercury (organic and inorganic), selenium, nickel, vanadium, and other metals upon request. These testing methods are based on the Environmental Protection Agency's (EPA) methods 200.11 and 7473.
Principles Of The Test
The total mercury (organic and inorganic) is determined without chemical pretreatment using thermal decomposition/atomic absorption spectrophotometry (TD/AA) technology. Homogenized fish samples are weighed into ceramic boats and introduced into the furnace; where the samples are dried and thermally and chemically decomposed. Oxygen flows through the furnace carrying the sample's decomposition products to the catalyst, which then oxidizes the decomposed products and traps halogens and nitrogen/sulfur oxides if present. The trapped halogens and nitrogen/sulfur oxides are then carried to the amalgamator, which contains gold particles with large surface areas, thereby allowing any mercury present to form a metal alloy with gold and becoming trapped in the amalgamator. Oxygen is used to flush the amalgamator to remove any remaining halogens and nitrogen/sulfur oxides and then the amalgamatory is rapidly heated causing the release of mercury, in the vapor form, from the gold particles. The vapor mercury is carried by flowing oxygen through two absorbance cells positioned in the light path of a single wavelength atomic absorption spectrophotometer; where the absorbance is measured twice at two different sensitivities, quantified, and processed by the instrument's data handling system.
For all other fish metal analysis, the laboratory analyzes homogenized fish samples using inductively coupled plasma mass spectrometry (ICP-MS). First, the fish samples are acid digested using microwave digestion and are then placed on the ICP-MS. From there the specimens are automatically pumped to the instrument nebulizer, which atomizes the solution into radio frequency plasma, where ionization takes place. Next, a vacuum interface pulls the ions through a series of cones and a focusing lens, where the positively charged ions enter the quadrupole and are separated by their mass-to-charge ratio. These ions are detected by an electron multiplier, quantified, and processed by the instrument's data handling system.
The technique used to collect fish must be free from contamination of metals. Individual tissue samples should be taken from fresh not previously frozen fish and soon after the fish is collected. If tissue cannot be taken immediately after collection, each fish should be placed in a plastic bag, sealed and placed on ice or refrigerated at 4°C.
Comments or questions regarding test results or testing methods contact the Trace Metals Unit
Keri Fisher, Analytical Chemistry Section Manager
Matt Geiger, Chemistry and Toxicology Division Director