Arsenic Contradiction and Beyond!

Arsenic contamination of underground water supplies is a major problem around the world. Studies of how different forms of arsenic deposit in the ground at different depths and move through the water system are helping prevent arsenic poisoning, especially in developing nations. Image : Researchers collect soil samples from bores in Bengal Basin, Bangladesh.
by Sanjeewa Gamagedara

(July 01, Washington DC, Sri Lanka Guardian) Several weeks ago, a team from University of Kelaniya revealed the presence of arsenic in drinking water in the Rajarata area and in commonly-used pesticides. Furthermore, they related this finding with Rajarata’s chronic kidney disease. Later, another investigation carried out by Industrial Technology Institute (ITI) found that arsenic is present only in two brands of pesticides out of about twenty eight. These studies have resulted in considerable enthusiasm in the media and among the general public. In this article, I do not expect to promote either of these studies, as I do not have access to those scientific data. However, I hope to explain some possible reasons for these contradictions and to delineate some future directions that we should follow in order to obtain reliable conclusions.

Arsenic, a chemical element with the symbol As, has the atomic number 33 and a relative atomic mass of 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It is poisonous to multi-cellular life due to the interaction of arsenic ions with protein thiols. Thus, arsenic and its compounds, especially trioxide, are used in the production of pesticides, herbicides, and insecticides. These arsenical pesticides have long been used in agriculture. The earliest recorded use of arsenic sulfides occurred in China as early as 900 A.D. Arsenous oxide was used at a rodenticide in the 16th century in Europe. These applications are declining, however, as many of these compounds are being phased out and banned in many countries.

Arsenic has been distributed widely in the environment due to both natural and anthropogenic activities, and it is often found in water, food, soil and airborne particles. The primary exposure pathway is ingestion by drinking water and eating food. Inhalation is regarded as a minor pathway, and dermal absorption is negligible. The toxicity of arsenic varies according to its valence, i.e. trivalent arsenics are more toxic than pentavalent arsenics, and the most toxic are the soluble arsenic compounds. The metabolism of arsenic plays a vital role in the manifestation of its toxic effects. Although the mechanism of arsenic in genotoxicity is not yet understood fully, researchers suspect that it is a result of arsenic’s ability to inhibit DNA from replicating or repairing enzymes and of arsenate’s action as a phosphate analog. Furthermore, the attack of mitochondrial enzymes by arsenic compounds, which results in impaired tissue respiration, can be tied to arsenic cellular toxicity. As with any other toxin, arsenic poisoning can be chronic or acute. Chronic exposure occurs over a prolonged period of time in smaller amounts, while acute exposure occurs all at once. Chronic arsenic exposure results in many symptoms, such as skin lesions, black-foot disease, peripheral neuropathy, hepatomegaly, cirrhosis, altered heme metabolism, diabetes, papillary and cortical necrosis and especially proximal tubule degeneration in the renal system. Arsenic carcinogenesis is also a major concern, causing tumors of the skin, lung, urinary bladder, liver, prostate, kidney and other sites. Arsenic is eliminated by urinary excretion; therefore, it can accumulate in the kidneys. Several studies have reported that arsenic compounds are cytotoxic to renal tissue at high concentrations. Thus, it potentially can cause of kidney disease. Detailed toxicological information is beyond the scope of this article, so we will move on to the possible causes for the contradictions in the recent arsenic studies.

Over the past several years, numerous and very important large-scale studies have been conducted without sufficient importance given to the analytical method used to obtain results. The quality of the outcome depends entirely upon the quality of the analytical data. However, detailed analytical method validation often is ignored in many studies. Without a proper method of validation and quality control, data means nothing. It is understood that both research groups used atomic absorption spectroscopy to quantify arsenic. Thus, we must ensure that both groups followed the proper method validation guidelines. The United States Environmental Protection Agency (EPA) defines the requirements for a valid atomic absorption quantification method. Arsenic analysis normally determines the total amount of inorganic arsenic (As), arsenite (As+3), arsenate (As+5), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). The applicability of any analytical method is governed by factors such as sensitivity, reliability of the analytical results, specificity or selectivity in the presence of interferences, operating range, rapidity and cost.

In such analytical methods, quality control (QC) should be maintained from the beginning to the end, i.e. from sample collection to waste removal. Some examples of quality control requirements are provided below. Samples should be collected into clean bottles and preserved in the field by adding hydrochloric acid. NaBH4 solution is added to convert inorganic As, MMA, and DMA to volatile arsines. Samples may become contaminated via numerous sources including metallic or metal-containing lab-ware, containers, sampling equipment, reagents, and reagent water, improperly cleaned and stored equipment, and atmospheric inputs such as dirt and dust. Contamination by carryover may occur when a sample containing low concentrations of As is processed immediately after a sample containing relatively high concentrations of As. Separate calibration curves should be constructed to detect As+3, As+5, MMA and DMA. Another important factor is that these calibrations should be matrix based in order to account for the matrix effect in the sample analysis. Otherwise, signal suppression or enhancement caused by the matrix effect will not appear in the results. The method detection limit, quantitation limit, precision and recovery in the real water matrix, and internal standard-based calibration are also important factors for meeting quality control requirements. Furthermore, each day before analyzing samples, researchers should verify the calibration by analyzing several standards. The detailed QC requirements can be found in the arsenic speciation EPA method. I hope both groups have satisfied the majority of these requirements in their studies.

If they suspect that people living in the Rajarata area were exposed to arsenic over a long period of time, they must conduct a detailed clinical study to detect arsenic levels in those patients’ bodies and compare them with healthy subjects in a different area. These results will determine whether any relationship exists between the arsenic and Rajarata’s chronic kidney disease. Invasive samples such as blood and tissue, as well as noninvasive samples such as urine, hair, and nails, can be used for this analysis. Urinary arsenic excretion varies inversely with the post exposure time period, but low-level excretion may continue for months after exposure. Even if the urinary arsenic measurements fall below accepted toxic levels, hair and nail analysis may be warranted. The highest concentrations of arsenic typically are deposited in hair and nails because of the high sulfhydryl content of keratin. Chronic ingestion of small amounts of arsenic results in the highest concentrations in hair, nails, and skin, tissues rich in cysteine containing proteins. Chronic accumulation also occurs in the lungs. In fact, scientists have analyzed arsenic in Napoleon Bonaparte’s hair even 150 years after his death.

This is a good eye opener to the research authorities to establish a sophisticated analytical lab with state-of-the-art analytical instruments and cutting-edge technologies. For example, this kind of elemental analysis can be done with more sensitive and accurate instruments, such as inductively coupled plasma mass spectrometry (ICP-MS). Then, a different method can be used in a different laboratory to check the validity of the results. Also, we must acquire a cutting-edge liquid chromatography tandem mass spectrometry (LC/MS/MS) system to detect other environmental contaminants present in very minute concentrations with more accuracy. Although I am not aware of current instrumentations available in universities, at ITI or in governmental analysis departments, I argue that authorities must improve those infrastructures because we are way behind compared to the modern world. As a country, we must prepare for the next challenge because, every day, most of us living in the cities drink chemical soups instead of pure water from the taps due to the pharmaceuticals and personal care products (PPCPs) in the drinking water. Generally, the term PPCPs refers to any product used by individuals for personal health or cosmetic reasons or used by agribusiness to enhance the growth or health of livestock. PPCPs constitute a diverse collection of thousands of chemical substances, including therapeutic drugs, veterinary drugs, fragrances and cosmetics. Studies undertaken in Europe, the U.S. and Canada have detected a wide range of PPCPs in surface water, groundwater and drinking water systems. Although the levels of these chemicals appear to be relatively low, due to their reactive nature, continual presence in the environment and unknown effects on both humans and aquatic ecosystems, concern is rising among researchers and health agencies. Failing to detect any contaminant with currently available instruments does not mean that drinking water is contaminant free. That is why we need more sensitive and accurate instruments and sample enrichment and purification methods, such as solid phase extraction (SPE), liquid-liquid extractions, and solid-phase micro-extraction (SPME). Let’s pray authorities will take necessary actions regarding these issues.

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