Barregård 1993: Biological Monitoring of Mercury Vapour—Blood, Urine, Amalgam, and CNS Risk

Why this review sits in the SMART reference pipeline

Reference #4 in the IAOMT Safe Mercury Amalgam Removal Technique (SMART) materials is Lars Barregård’s 1993 review Biological monitoring of exposure to mercury vapor, in the Scandinavian Journal of Work, Environment & Health (1993;19 suppl 1:45–49). From Sahlgren’s University Hospital in Göteborg, Sweden, it synthesizes how blood mercury (B-Hg) and urine mercury (U-Hg) track inhaled elemental mercury vapour—and how those markers relate to exposure, body burden, and adverse-effect risk.

Three statements drive its value for dental mercury education:

1. Dentistry accounts for the largest number of workers occupationally exposed to mercury vapour (even when typical dental air levels are lower than chloralkali plants or mercury mines).
2. Where amalgam is used, release from dental amalgam is the major source of inorganic mercury in the general population.
3. Monitoring U-Hg is useful for assessing the risk of adverse effects and the need for preventive measures—including at average levels around 50 µg·g creatinine⁻¹, where CNS and urinary-protein signals increase.

That is biomonitoring aimed at exposure control, not at treating dental mercury vapour as trivial.

What biological monitoring measures

Barregård frames biological monitoring as assessing (i) exposure, (ii) absorbed dose / body burden / critical-organ concentration, or (iii) risk of adverse effects. Practical media are urine and whole blood. Contamination control is crucial: occupational urine samples should be collected at home after hand washing; first-morning spot urine corrected for creatinine (or specific gravity) is the recommended practical surrogate; blood belongs in mercury-free heparinized vacutainers in an uncontaminated setting. Standard analysis is cold-vapour atomic absorption spectrophotometry (typical detection ~0.5 ng·g⁻¹, precision ~5%).

Blood vs urine: complementary vapour markers

Blood mercury tracks recent peaks

After vapour inhalation, absorption is rapid and B-Hg rises quickly. After a single low-level episode, peak B-Hg appears on the exposure day and falls with a half-time of about 3 days. After 3 days of high exposure (>100 µg·m⁻³), blood elimination fits a two-compartment model (~3 and 18 days), the fast phase ~80% of the initial maximum. After long-term exposure, the fast phase still has a similar half-time but accounts for only about half of B-Hg when exposure ceases. B-Hg is therefore an excellent indicator of recent exposure peaks.

From blood, vapour distributes to tissues, oxidizes to bivalent mercury, and binds proteins; over time much of the burden concentrates in the kidneys. Elimination is mainly via urine and feces.

Urine mercury tracks average long-term load

Urinary excretion involves tubular processes, so U-Hg rises later than B-Hg. After short-term exposure, maximum U-Hg may not appear for several weeks. Half-time after short-term exposure is about 40–60 days (one-compartment); after long occupational exposure, about three months. That delay smooths day-to-day air swings: flow-corrected U-Hg is valuable for average long-term exposure, weaker for brief peaks. Barregård’s operational conclusion: B-Hg or U-Hg monitoring is suitable for assessing mercury-vapour exposure when kinetics and variation sources are respected.

Amalgam, fish, and background levels

In occupationally unexposed people with low/moderate fish intake, approximate averages near the review were B-Hg ~3 µg·L⁻¹ and creatinine-corrected Swedish U-Hg ~2–3 µg·g⁻¹.

Two confounders dominate:

• Fish / methylmercury inflate total B-Hg—often half or more—so total blood mercury is a poor low-level vapour tool unless inorganic and organic fractions are separated.
• Dental amalgam is the major inorganic source for the public where amalgam is used. Assessing other low-level inorganic exposures requires recording and adjusting for dental status.

Dental-personnel data Barregård cites show a clinician’s own amalgam fillings and occupational exposure contribute to U-Hg to about the same extent. Patient amalgam burden and operatory vapour stack.

Under relatively constant long-term exposure, a quality-controlled study he judges especially reliable reported air (µg·m⁻³) : U-Hg (µg·g creatinine⁻¹) : B-Hg (µg·L⁻¹) ratios of about 1 : 1.22 : 0.45, with dental-personnel air-to-urine ratios of similar magnitude.

One urine number is not enough

Day-to-day B-Hg variation is moderate (~10% CV under stable exposure). U-Hg variation is larger—typically 15–20% even when corrected—so consecutive days often differ by ~25% and sometimes ~50%. For individuals (and for dose–response work), Barregård’s fix is clear: use the average of several measurements.

CNS and kidney signals at monitored urine levels

Acute very high vapour causes pneumonitis. Classic chronic poisoning—erethism, tremor, gingivitis—has been known for centuries; nephritis and allergic dermatitis are also recognized. By the early 1990s, frank classical poisoning was rare in many countries, but subtle CNS and renal effects remain the biomonitoring target.

Anchors from the review:

• Group-average U-Hg above ~300 µg·L⁻¹ has been linked to high (>10%) poisoning frequency.
• Increased symptoms and slight objective CNS changes appear with long-term vapour above ~50 µg·m⁻³, producing U-Hg in the 50–100 µg·g creatinine⁻¹ range (fatigue, memory disturbance, tremor). Some studies suggest effects at even lower levels.
• Elevated high-molecular-weight urinary proteins or tubular enzymes occur at similar or slightly lower exposure; enzymuria may be among the earliest objective effects.
• At average U-Hg ~50 µg·g creatinine⁻¹ (28 nmol·mmol creatinine⁻¹), prevalence of symptoms and slight objective CNS changes and excretion of certain urinary proteins are increased.
• Proposed biological exposure limits of 50 and 35 µg·g creatinine⁻¹ are cited (WHO study-group and BEI-committee figures).

Barregård’s close is direct: many studies show a relation between U-Hg and CNS/kidney effects; biological monitoring is suitable for assessing adverse-effect risk and implementing preventive measures. Quantitative fluid-to-critical-organ links were poorly constrained; local effects such as pneumonitis or dermatitis are not usefully tracked by these markers.

Why this matters for dental mercury and SMART hygiene

SMART measures—isolation, high-volume evacuation, water coolant, filtration, respiratory protection, barriers, and amalgam waste control when amalgam is removed or disturbed—follow the same occupational logic: respect vapour kinetics and prevent when monitored burden approaches levels linked to adverse effects.

Practical takeaways

1. Mercury vapour is absorbed and measurable—blood for recent peaks; corrected urine for long-term inorganic load.
2. Amalgam is a major inorganic source for the public—and a dual contributor for dental staff.
3. Average several urine results before individual conclusions.
4. Around ~50 µg·g creatinine⁻¹, Barregård’s synthesis already shows increased CNS and urinary-protein signals—the zone where preventive action is medically rational.
5. Biological monitoring exists to assess risk and drive prevention, including in dentistry, the largest vapour-exposed occupational group he names.

Bottom line

Barregård 1993 states the biomonitoring case plainly: inhaled mercury vapour leaves a readable trail in blood and urine; dental amalgam is the dominant inorganic source for much of the public; dentistry concentrates occupational vapour exposure across many workers; and urine monitoring in the tens of micrograms per gram creatinine is already where CNS and renal signals rise—and where prevention is warranted. For thesmartchoice.com / IAOMT SMART readers, Reference #4 turns “mercury vapour from amalgam” into a measurable exposure and risk-management problem.

Citations

1. Barregård L. Biological monitoring of exposure to mercury vapor. Scand J Work Environ Health. 1993;19(suppl 1):45–49. PMID: 8159972. DOI: 10.5271/sjweh.1532.
   • Journal / PDF: https://www.sjweh.fi/article/1532
   • PubMed: https://pubmed.ncbi.nlm.nih.gov/8159972/
2. Kinetics studies Barregård synthesizes:
   • Barregård L, Sällsten G, Schütz A, Attewell R, Skerfving S, Järvholm B. Kinetics of mercury in blood and urine after brief occupational exposure. Arch Environ Health. 1992;47:176–184. https://doi.org/10.1080/00039896.1992.9938347
   • Sällsten G, Barregård L, Schütz A. Decrease in mercury concentration in blood after long term exposure: a kinetic study of chloralkali workers. Br J Ind Med. 1993;50:814–821. https://doi.org/10.1136/oem.50.9.814
3. Dental dual contribution (own amalgam + work) cited by Barregård:
   • Åkesson I, Schütz A, Attewell R, Skerfving S, Glantz PO. Status of mercury and selenium in dental personnel: impact of amalgam work and own fillings. Arch Environ Health. 1991;46(2):102–109. https://doi.org/10.1080/00039896.1991.9937436
4. Air–urine–blood ratio study Barregård highlights:
   • Roels H, Abdeladim S, Ceulemans E, Lauwerys R. Relationships between the concentrations of mercury in air and in blood or urine in workers exposed to mercury vapor. Ann Occup Hyg. 1987;31:135–145.
5. International Academy of Oral Medicine and Toxicology (IAOMT). The Safe Mercury Amalgam Removal Technique (SMART) reference list (Barregård 1993 as Reference #4).

Scope note: Thresholds and kinetics above are from Barregård’s 1993 review and studies it cites; this article does not invent patient-level outcomes from SMART procedures.