Mercury being a heavy metal is highly carcinogenic and its presence in water sources and the tissues of aquatic species especially fish is a serious health concern. According to EPA, the acceptable maximum concentration for mercury is 0.3mg/kg (UDWQ), and therefore accurate, valid, and reliable techniques for analyzing mercury levels are essential. Currently, two methods are available for quantitative mercury analysis. The cold vapor technique which is used by EPA and United State Geological Survey (USGS) is the oldest method used to quantize mercury levels in tissue samples. In this technique, digested samples are analyzed using a cold vapor atomic absorption spectrometer to determine mercury concentration.
The second technique called thermal decomposition uses an automatic mercury analyzer to measure mercury absorbance at a specific wavelength in AAS. This technique is used in the UDOH laboratory, Arizona Department of Health Services (ADHS) and in Texas A & M. This method is also used in EPA laboratories. Although no method can be said to be better than another since the standard deviation between them ranges from 0.01 to 0.007, the cold vapor method however yields slightly lower values. The standard deviation for thermal decomposition ranges from 0 to 0.06ug/g and 0.01 to 0.11ug/g for cold vapor (UDWQ). For quality checks, both methods need to be used.
The accuracy of an analytical technique lies centrally on the sampling methods and sample pre-treatment procedures. A flawed sampling method gives invalid results that are do not represent elemental concentration in the sample. It is therefore imperative that due care and emphasis be laid on sampling. Samples should be representatively collected and wrapped to avoid contamination. Sample identifications should reflect the sampling site, the sample ID code, and the sample sequence number. Quality control checks should also be done to identify if any contamination occurred during sample handling, storage, and analysis.
For validity and reliability of the results, sample blanks are analyzed alongside the samples to ensure that no contamination is carried over to the next sample and also to check the accuracy of the analytical instruments used. The Standard Operating Procedures (SOP), as well as the Quality Assurance and Control procedures, should be followed. For method validation, spiked samples, sample duplicates, and standards whose concentrations are known are also analyzed (UDWQ).
To verify initial results, repeatability and reproducibility studies must be carried out to obtain commensurate results. This serves to show inherent flaws in the experimental procedures and methods used besides ensuring that analysts pay diligence to the experimental design process. This is however costly and time-consuming since reproducibility studies require independent researchers and different instruments to avoid inherent flaws which might be present in the initial instrument. Alternatively, UDOH can train its scientist to be better equipped to carry out repeatability and reproducibility studies.
Additionally, for purposes of quality check, duplicate samples should be analyzed in different laboratories to make a comparison between UDOH results and those obtained by these laboratories. This is a laborious and costly process since duplicate samples have to be prepared and payment made for such analysis. Ideally, the standard deviation between these labs should be low and with high precision. Standard deviation should also be determined between similar methods and should be within the allowable limits determined for results to be valid.
Based on the laborious, time-intensive, and overall cost for carrying out sampling, sample analysis, comparative analysis in different labs, and repeatability and reproducibility studies, all of which are meant to determine the accuracy and reliability of the results, adequate funds must be a channel to UDOH. Funds will also be used in training UDOH analysts to be better equipped to carry out method validation through repeatability and reproducibility studies.
Works cited
UDWQ, 2006. Water Quality Department. Web.