ICP-MS Plays a Vital Role in the Investigation of Lead Levels in a Drinking Water Supply

This article describes how breakthroughs in atomic spectroscopy, and in particular ICP-MS, have led researchers to a better understanding of environmental pollution and the effects of trace metals on humans. It focuses on the toxic effects of lead and how regulatory toxicity levels have been lowered as new, more sensitive instrumentation has been developed. To exemplify this, it features a case study of how one water municipality used ICP-MS to analyze over 60,000 drinking water samples for Pb, in an investigation into the impact of the plumbing systemon the water supplies of the public schools.

The development of analytical instrumentation over the past 40 years has allowed us not only to detect trace metals at the parts per quadrillion (ppq) level, but also to know its valency state, biomolecular form, elemental species, or isotopic structure. We take for granted all the powerful and automated analytical tools we have at our disposal to carry out trace elemental studies on clinical and environmental samples. However, it was not always the case. As recently as the early 1960s, trace elemental determinations were predominantly carried out by traditional wet chemical methods like volumetric-, gravimetric-, or colorimetric-based assays. It was not until the development of atomic spectroscopic (AS) techniques, in the early 1960s, that the clinical and environmental communities realized they had such a highly sensitive and flexible trace-element technique. Every time there was a major development in atomic spectroscopy — such as flame atomic absorption (FAA), electrothermal atomization (ETA), inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS) — trace-element detection capability, sample throughput, and automation dramatically improved. There is no question that developments and breakthroughs in atomic spectroscopy have directly impacted our understanding of environmental contamination and the way trace metals interactwith the human body.

LEAD
Take for example, the toxicity effects of lead (Pb), espe cially in young children.It can damage a child's central nervous system, kidneys, and reproductive system and, at higher levels, can cause coma, convulsions, and even death. Lead has no known biological or physiological purpose in the human body, but is avidly absorbed into the system by ingestion, inhalation, or skin absorption. Children are particularly susceptible, because of their playing and eating habits. Lead is absorbed more easily if there is a calcium/iron deficiency, or if the child has a high fat, inadequate mineral, and/or low protein diet. When absorbed, lead is distributed within the body in three main areas — bones,blood, and soft tissue. About 90% is contained in the bones, while the majority of the rest gets absorbed into the bloodstream where it gets taken up by porphyrin molecules (complex nitrogen-containing organic compounds that provide the foundation of hemoglobin) in the red blood cells. It is therefore clear that the repercussions and health risks are potentially enormous, if childrenare exposed to abnormally high levels of lead.

The level of lead in someone’s system is confirmed by a blood-lead test,which by today’s standards is considered elevated if it is in excess of10 µg/dL (100 ppb) for children and 40 µg/dL (400 ppb) for adults.However, since 1970, our understanding of childhood lead poisoning has changedsubstantially. As investigators have had more sensitive techniques at their disposaland designed better studies, the toxicity levels for lead have progressivelyshifted downward. Before the mid-1960s, a level above 60 µg/dL (600 ppb)was considered toxic and by 1978, the defined level of toxicity had declined50% to 30 µg/dL (300 ppb). In 1985, the CDC published a threshold levelof 25 µg/dL (250 ppb), which they eventually lowered to 10 µg/dL(100 ppb) in 1991. It is well-recognized that the development of flame atomicabsorption in 1962 to the detection limit breakthrough of electrothermal atomizationin 1971 and the staggering sensitivity and sample throughput of ICP-MS in 1983have all played an integral part in reducing these toxicity levels.

TOXICITY LEVELS
Even though the majority of sources of lead contamination have essentially been removed from the environment, (e.g., paint, pipes, gasoline, pottery, smelters), there still remains a potential threat from the use of lead plumbing materials used in drinking water supplies. This is definitely the case with older buildings, but can also be a problem with newer homes that use copper pipes and fittings connected with lead-based solders.

This has been recognized by regulatory standards even as far back as the early 1960s, when the Surgeon General under the direction of the U.S. Public Health Service set a mandatory requirement for Pb levels in drinking water. Unfortunately at that time, lead assays were carried out using the dithizone colorimetric method, which was very sensitive but extremely slow and labor intensive. It became more automated when anodic stripping voltammetry was developed but lead analysis was not considered a truly routine method until AS techniques became commercially-available in the early 1960s. It was not until 1974, when Congress passed the Safe Drinking Water Act (SDWA), that the National Primary Drinking Water Regulations set Maximum Contaminant Levels (MCLs) of 50 ppb for Pb. At this point in time, ETA was firmly established as the dominant ultra-trace element analytical technique and even though it could detect these kinds of levels with relative ease, it was extremely slow and labor-intensive. This did not pose a real problem for small numbers of samples, but as a duplicate analysis might take five to seven minutes per sample, it became very time-consuming in high-workload environments.