Contribution of Lead in Wine to the Total Dietary Intake of Lead in Humans with and without a Meal - a pilot study

Brian L. Gulson^1,4, Creina S. Stockley², Brian Gray³, Karen J. Mizon^{4 ,} Nicole Patison⁴

¹ Graduate School of the Environment, Macquarie University, Sydney NSW, 2109, Australia (bgulson@gse.mq.edu.au); ² The Australian Wine Research Institute, South Australia, Australia; ³ School of Chemistry, Macquarie University; ⁴ CSIRO Division of Exploration and Mining, POB 136, North Ryde NSW 1670, Australia

Abstract

We have undertaken a pilot case-control study using high precision lead isotopes to evaluate the contribution to blood lead when a normal quantity of wine is consumed with a meal and compared this with consumption under fasting conditions. White wine dosed with a ²⁰⁷Pb tracer was consumed with a meal and under fasting conditions and blood, urine and faeces monitored for up to four months. Approximately equal proportions of unspiked red and white wine were consumed over the four months by the subject and a female subject residing in the same household. The blood lead concentration of the case subject was 4.1 mg/dl and 3.4 mg/dl in the control subject. No increase in the concentration of lead in blood for the wine consumed with a meal was detectable but there was a ~6% increase in blood lead concentration for wine consumed under fasting conditions. When consumed with a meal, the percentage absorption at 24 hours was only 2.3%, compared with approximately 34% under fasting conditions.

Introduction

Lead is a neurotoxin with no known beneficial biological role. Young children and the developing foetus are considered to be most at risk from the toxic effects of lead. In adults, foods and beverages are the primary pathways of exposure to lead although recent evidence indicates that the skelton is the dominant source of lead in blood (e.g. Gulson et al., 1995). The Provisional Tolerable Weekly Intake (PTWI) for lead in adults is 25 µg/kg body(FAO/WHO 1990). While lead in foods and beverages per se has been reduced to a level relatively innocuous to adults, it has been suggested that lead in wine has become an important exposure route for dietary lead. For example, it has been claimed that wine could constitute a major source of lead for moderate consumers of wine, that is, at least 50% of the dietary intake for those people not occupationally exposed (Elinder et al. 1988, Smart et al. 1990, Newton et al. 1992). Wine consumers constitute approximately 75% of the Australian adult population and approximately 85% of the population who consume wine do so with food. For a moderate consumer of wine who has an average daily intake of wine is 0.5 L (three glasses), the daily intake of lead from wine is calculated to be approximately 20 µg, less than 25% of the average daily dietary intake in Australia as the mean concentration of lead in Australian wines is below 40 µg/l. A pilot study was undertaken to determine the impact on blood lead concentration (PbB) resulting from consumption of wine when consumed in moderate amounts, with and without food.

Methods

A wine (115 mg Pb/l) made from the variety Riesling was “spiked” with pure ²⁰⁷Pb. The study was carried out in two phases, one with food and the other under fasting conditions. In the “food” experiment, unspiked wine was administered daily with food for 1 month to establish a background. The spiked wine was then consumed by the male with food (meat, gravy, toast, coffee) on one occasion in the morning. His PbB was 4.1 mg/dl in the food experiment and had decreased to 2.6 mg/dl over the 3 years to the fasting experiment. A bottle (750 ml) of either red or white wine from the same vintage and vineyard was consumed daily over 4 months by the subjects. Samples of blood, urine and faeces were collected predose and at regular intervals postdose for an initial 48 h period, and blood and urine were collected fortnightly for 3 months. A female living in the same household was enlisted as a control over the 4 months of the study (PbB 3.4 mg/dl). She consumed the same diet, including unspiked wine, as the male but only blood samples were collected and at limited intervals compared with the case subject. In the fasting experiment, blood and urine samples were collected for 1 week for the case subject. No samples were taken for the control subject because of the lack of any change observed in the earlier experiment. Lead isotopic ratios and lead concentrations were measured by thermal ionisation mass spectrometry (Gulson et al., 1992).

Results and Discussion

Wine with a meal: . The mean and standard deviation for 23 samples of blood collected over a 6 week period was 4.17 ± 0.18 mg/dl. Because of the minimal changes in PbB concentration and the relatively small isotopic changes, it was not feasible to express the variations in PbB due to the administered dose in terms of the % abundance of ²⁰⁷Pb. Hence as the ²⁰⁷Pb/²⁰⁴Pb ratio in blood and urine prior to the experiment was 15.48 compared with that in the doped wine of 355, these large differences allowed for easily discernible changes in the ²⁰⁷Pb/²⁰⁴Pb ratio. The variations in tracer lead denoted by the ²⁰⁷Pb/²⁰⁴Pb ratio are shown in Figures 1 through 3. Using the ²⁰⁷Pb/²⁰⁴Pb ratio, the uptake into, and clearance of tracer lead from, blood followed a first-order kinetic function (Figure 1) with the uptake more than twice as rapid as the clearance , a condition found in other studies (Chamberlain 1985). The half-life for the uptake of the lead into blood was 8.6 ± 1.7 hours with a rate constant of 0.08 ± 0.02 /hour. For the clearance of lead from blood, the half-life was 23 days with a rate constant of 0.21/week, consistent with the mean of 18 days for 5 subjects subjected to chronic lead doses by Rabinowitz et al (1976) and slightly lower than the 30 days for chronic lead ingestion from beer (Newton et al., (11). The tracer dose in blood attained a maximum at 36 hours (Figure 1), similar to the time of maximum observed for single dose experiments with ²⁰³Pb tracer such as Newton et al.(11). By 24 hours, 1.3% of the administered lead dose was in the blood compartment. Following the same calculations of Graziano et al. (20), the fractional absorption of lead from the wine was only 2.3%. The maximum excretion of tracer lead was observed at 6.4 hours (Figure 2), similar to that observed by other investigators (e.g. Chamberlain et al. 1979). In 24 hours, approximately 0.12 mg ²⁰⁷Pb tracer was excreted (approximately 0.4%) compared with 2 to 3% of a systemic dose excreted in 24 hours for ingestion of ²⁰³Pb. The renal clearance expressed as the amount of lead excreted over the whole PbB was 0.08 l/day or 3.3 ml/hour. These results compare with the value of 0.11 kg/day or 4.3 ml/hour given by Chamberlain 1985). Approximately two weeks after the dose was administered, the continuous decline in excretion rate of ²⁰⁷Pb tracer lead reached a plateau.

Wine consumed under fasting conditions:- The maximum tracer dosage of lead in blood for the wine consumed under fasting conditions was attained at 24 hours (Figure 3). By 24 hours, 19% of the administered dose was present in the blood compartment, giving a fractional absorption of about 34%. The uptake of tracer lead into blood conformed also to a (reversible) first-order absorption process with a half-life of 5.4 ± 1.5 hours and rate constant of 0.13 ± 0.04 /hr. As regular monitoring was not continued past 7 days, the clearance rate of lead from the blood compartment was not calculated. In contrast to the wine consumed with a meal, there was a significant increase of about 6% in the PbB concentration with the maximum reached at 10 hours, a time similar to that observed by Graziano et al. (1996).

Graziano et al. (1996) found that in sherry which had been stored in a lead crystal decanter for 3 years and consumed under fasting conditions, the average contribution to the blood compartment of the administered dose was 38% and proportion absorbed in the gastrointestinal tract ranged from 46 to 96%. These values are considerably higher than we observed but are possibly the result of the higher dose of lead from the sherry (250 mg vs 30 mg Pb) and differences in bioavailability of the lead in the sherry derived from the lead crystal decanter. Another explanation for the difference is individual susceptibility as shown by the range from 46 to 96% in the amount absorbed by different individuals in the sherry experiment of Graziano et al. (1996).

Excretion through faeces was monitored only for 2 days so that the amount of unabsorbed tracer lead excreted over the 2 days of >60% was a minimum. Rabinowitz et al. (1980) found more than 80% of ingested lead administered as the stable isotope was excreted in days 1 to 5. In these tracer load tests, Rabinowitz et al. (980) found that only 8 to 10% of the ingested dose was absorbed when taken with food. Chamberlain et al. (1978) observed the maximum faecal excretion at 2 days after a dose was administered by inhalation and 3.5 days by injection.

Thus in the current experiment of a single dose of tracer lead in white wine consumed with food, the contribution to PbB from wine containing “normal” amounts of lead (<100 mg Pb/l) was minimal. The amount of tracer lead observed in the blood at 24 hours was less than 3% of the administered dose. So that in spite of wine potentially contributing up to 25% of the average daily dietary lead intake, if consumed with food, the amount of lead absorbed is small and contributes minimally to blood lead concentrations.

Acknowledgements:We wish to thank: The Australian Wine Foundation of Australia and The Grape and Wine Research and Development Corporation for financial support, Michael Korsch for maintaining the mass spectrometers in peak condition and software developments, and Mary Salter for phlebotomy.

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Figure 1. Time-series plot for the ²⁰⁷Pb/²⁰⁴Pb ratio in blood for wine doped with ²⁰⁷Pb was consumed with a meal. The small amount of uptake of lead from the wine is shown by the limited change in the ²⁰⁷Pb/²⁰⁴Pb ratio in blood compared with a value of 355 in the wine. The data for the treatment subject are compared with the control subject. The time axis is not proportional.

Figure 2. Time-series plot showing the changes in ²⁰⁷Pb/²⁰⁴Pb ratio for blood for white wine consumed under fasting conditions. Note difference in scale on Y-axis compared with that in previous figures.