"Arsenic concentration in seafood using ICP-AES"
Arsenic concentration in seafood using ICP-AES Ava Heydt-Benjamin, Sunyoung Bang, Christopher Griffin, Elena Dodova Our group is investigating methods of analysis of arsenic (As) in food using Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). Arsenic is an element that is largely contained in the earth's crust, so it is naturally found in soil and minerals, therefore it may be in air, water, and wind-blown dust. Arsenic is usually found combined with other elements such as oxygen, chlorine, and sulfur. Arsenic combined with these elements is known as inorganic arsenic. Arsenic combined with carbon and hydrogen is referred to as organic arsenic. Organic forms are usually less harmful than the inorganic forms of As (1). Many scientists study As due to its relevance in human health issues such as arsenicism (slow poisoning by arsenic), which is linked with different forms of cellular epithelial disease leading to eventual carcinoma. Ingestion of arsenic is theorized to increase the risk of cancer in many body systems. Especially at risk are the liver, bladder, kidneys, prostate, and lungs (1). The fact that inorganic arsenic may be found in up to 21- 40% of the total diet (2) suggests that research in this area of is important. Arsenic levels in excess of 10 parts per billion (ppb) are suspected of causing harm to humans (Current U.S. Environmental Protection Agency standard) (3). The papers which we examined showed a high incidence of naturally occurring As in fish and seafood. These high concentrations of As are due to bioaccumulation in the aquatic organisms. Few papers have been written on arsenic levels in other foods, possibly because dangerous arsenic contamination is less common in other foods. One interesting paper (4) examines arsenic bioaccumulation in fish living in a freshwater lake located near a volcanic source of arsenic. The water in this lake is naturally acidified, with low levels of phosphorus. Because of the chemical similarities between phosphorus and arsenic, the authors of the article suspect that arsenic may have taken the place of phosphorus in certain metabolic activities. This is likely only to happen in environments when phosphorus is scarce. ICP-AES analysis is generally superior in its accuracy, precision, and lower limits of detection. This technique is less prone to interference than those preformed using other analytical instrumentation. One can analyze a solution for many elements in 1 minute. Therefore, large volumes of data can be generated very fast. ICP-AES uses plasma generated from gas in which the atoms are present in ionized or semi-ionized forms. There are loops that form a torch, through which gas flows into a coil and becomes electrically conductive. This allows for r.f. field (radio frequency generator) to activate for reading. With ICP-AES the detection limit varies, 0.5 ~ 1.0 µg/l for As (5). As with any analytical chemistry procedure the sample has to be prepared in a way which is appropriate for the instrument. To perform analysis using this spectroscopic technique, the sample must first be homogenized. After homogenization, the sample must be digested. The two principle techniques for digestion are known as “wet ashing” and “dry ashing” respectively. In wet ashing, the sample is digested with strong acid at high temperature. In dry ashing, the sample undergoes pyrolysis, which is a process of burning at high temperate in a furnace. A drawback to dry ashing is the possibility of losing substances from the sample due to vaporization. After digestion, the resultant ash must be dissolved in an aqueous solution. This solution is then atomized into fine droplets inside the spectrometer, where it comes into contact with a partially ionized argon plasma at very high temperature. This causes the sample to emit light at frequencies characteristic of the elemental composition. Computer interpretation of these spectral patterns allows the analytical chemists to determine the concentration of elemental arsenic present in the samples. Prior to gathering of experimental data, the equipment is calibrated by measurement of a standardized sample of accurately known arsenic concentration (6). After examining different experimental results, it is clear that As is harmful in many ways. Since ingestion is the primary means of exposure to As in humans, determining its concentration, and bioavailability in foods may help increase awareness of health threats due to previously inadvertent poisoning. 1. ATSDR (Agency for Toxic Substances and Disease Registry): “Public Health Statement for Arsenic”, Document number CAS# 7440-38-2, September 2000, http://atsdr1.atsdr.cdc.gov/toxprofiles/phs2.html 2. Deoraj, Caussy: “Case studies of the impact of understanding bioavailability: arsenic”, Ectotoxicology and Environmental Safety 56 (2003) 164-173 3. A.Mushtaque et al.,”Arsenic Crisis in Bangladesh”, Scientic America Vol. 291 #2 86-91 4. Akiko Takatsu, et al. “Abnormal arsenic accumulation by fish living in a naturally acidified lake”, The Analyst, January 1998 Vol. 123 (73-75) 5. Chemical Properties, appendix;04.14 http://tmecc.org/documents/ICP_Appendix.pdf 6. http://www.braford.ac.uk/acd/chemistry, (accessed 10/12/2004)