Part B - Metals  

Figure 6: Range of mean estimated dietary exposure to metals for infants (9 months) as a percentage of the tolerable limit , based on median analytical results

Antimony

Antimony is found in low-level concentrations in water, soil and air. It is also widely used as an industrial chemical in the manufacture of alloys and in the production of fireproofing chemicals and textiles (ANZFA 1999).

The FAO/WHO Joint Expert Committee on Food Additives has not made any evaluations of antimony and therefore no tolerable limit has been set. However, an oral reference dose for antimony of 0.4 µg/kg bw/day was assigned by the United States Environmental Protection Agency (USEPA 1991). This level has been adopted by FSANZ as a tolerable limit for the purposes of dietary modelling.

The mean, median, maximum and minimum levels of antimony found in foods analysed in the 20^th survey are given in Part 2 (Table 8) of the Supplementary Information (FSANZ 2002).

The estimated dietary exposures to antimony for each age–gender category are given in Appendix 1. All estimated dietary exposures were below the tolerable limit for antimony. The highest calculated mean exposure to antimony was for infants because of their high food consumption relative to body weight. The calculated exposure for infants was a wide range (3% to 61% of the tolerable limit). The lower limit was calculated by assuming that foods contained no antimony if they were reported as containing less than the LOR (0.002 mg/kg) and the upper limit was calculated by assuming that foods contained 0.002 mg/kg of antimony if they were reported as containing less than the LOR. The large range results from limitations of the analytical method, which measured antimony levels down to 0.002 mg/kg, and the high proportion of results that were reported as less than the LOR. The actual dietary exposure for antimony lies within this calculated range and it is not possible, with the current method, to be more precise.

In the 19^th ATDS, a wider range was reported for antimony dietary exposures and, for some age-gender categories, the range extended above the acceptable health standard. Refinements to the analytical methods and consequent lower limits of reporting for antimony in this survey have enabled a more refined dietary exposure estimate to be made for antimony. The refinements in the 20^th ATDS have established that the dietary exposure to antimony for all age-gender categories is within acceptable health standards.

Arsenic

Arsenic occurs naturally in both organic and inorganic forms. Inorganic arsenic is more toxic than organic arsenic. In the past, arsenic compounds were commonly used in drugs, but the more recent major uses are in pesticides, veterinary drugs and industrial applications (WHO 1981). Inorganic arsenic is registered for use in timber preservatives and for control of termites in timber. There are no registered uses in food crops or for animal production. DSMA (disodium methyl arsonate) is registered as a herbicide for turfs and lawns. MSMA (monosodium methyl arsonate) is registered as a herbicide for use in cotton and sugarcane production, on rights-of-way and for non-crop uses.

Generally, most foods contain low levels of arsenic due to its wide distribution in the environment and, to some extent, to its use in agriculture. Dietary arsenic represents the major source of arsenic exposure for most of the population. Some types of seafood contain up to 10 times the arsenic of other foods. People who consume large amounts of seafood may therefore ingest significant amounts of arsenic. The arsenic in seafood is primarily in the organic form.

The 20^th ATDS examined total arsenic in all foods and inorganic arsenic in fish portions, fish fillets, prawns, and canned tuna. Inorganic arsenic was only measured in seafood because of the generally higher levels of arsenic that these foods contain and to identify the quantities of the more toxic inorganic arsenic in these foods. The mean, median, maximum and minimum levels of total arsenic and inorganic arsenic found in the foods analysed are given in Part 2 (Tables 9 and 10) of the Supplementary Information (FSANZ 2002). The estimated dietary exposure to total arsenic for each age–gender category is given in Appendix 1.

A level of 0.003 mg/kg bw/day was determined to be the tolerable limit for inorganic arsenic, based on a review of available epidemiological data (ANZFA 1999). Inorganic arsenic analyses are more expensive than total arsenic analyses. To make the best use of the available funds for analytical testing, total arsenic, rather than inorganic arsenic, is determined in most cases. There is no accepted ratio that can be used for all foods to convert the total arsenic content to inorganic arsenic. For this reason and to enable comparison of the results with the tolerable limit for inorganic arsenic, it was assumed that all arsenic detected in each food was in the form of the more toxic inorganic arsenic. This is a significant overestimate because not all arsenic is present as inorganic arsenic. This is demonstrated by the presence of total arsenic at levels above the LOR in all of the seafood samples while inorganic arsenic was not present above the LOR in any of the seafood samples. In the 20^th ATDS, the seafood samples surveyed (fish fillets, fish portions, prawns, and canned tuna) contained the highest levels of total arsenic in comparison to the other foods surveyed. The mean level of total arsenic present in seafood was between 4 and 68 times higher than the highest mean level found in non-seafoods. In the 20^th ATDS, seafoods contributed to approximately 35% of total arsenic intake for infants, toddlers and girls aged 12 years, approximately 50% for boys aged 12 years, 65% for adult females, and 70% for adult males.

Even with the overestimation for inorganic arsenic content, all estimated dietary exposures to total arsenic were below the tolerable limit for inorganic arsenic. The highest mean exposure to arsenic was for infants because of their high food consumption relative to body weight. This exposure ranged from 12% of the tolerable limit up to 48%. The wide range results from limitations of the analytical method, which measured arsenic down to 0.01 mg/kg, and the significant proportion of results reported as ‘less than the LOR’. Dietary exposures to arsenic are within acceptable health standards.

Cadmium

Cadmium is a metallic element that occurs naturally at low levels in the environment. Food, rather than air or water, represents the major source of cadmium exposure, although tobacco smoking adds significantly to the body’s burden. Long-term exposure to high levels of cadmium may lead to considerable accumulation in the liver and kidneys, particularly the renal cortex, resulting in kidney damage (WHO 1989b).

Additional cadmium has been added to the environment through industrial processes such as cadmium metal production. Further cadmium has been added to agricultural soils through the use of phosphate fertilisers (WHO 1989b) and certain organic fertilisers based on manures.

The tolerable limit for cadmium, which was set at the 33rd meeting, was maintained at the 55th meeting of the FAO/WHO Joint Expert Committee on Food Additives at 7 µg/kg bw/week (WHO 2001b).

The mean, median, maximum and minimum levels of cadmium found in the foods analysed are given in Part 2 (Table 11) of the Supplementary Information (FSANZ 2002). The estimated dietary exposures to cadmium for each age–gender category are given in Appendix 1.

All estimated dietary exposures to cadmium were below the tolerable limit of 7 µg/kg bw/week, and are consequently within acceptable safety standards. The highest mean exposure to cadmium was for infants because of their high food consumption relative to body weight. This exposure ranged from 13% to 68% of the tolerable limit. This range results from limitations of the analytical method, which measured cadmium levels down to 0.005 mg/kg, and the significant proportion of results reported as ‘less than the LOR’.

Copper

Copper is widely distributed in nature. Copper can be released into the soil via mining, agriculture and waste from treatment works (WHO 1998). Copper and its compounds have many industrial, urban and agricultural uses. Copper salts, in the form of Bordeaux mixture, have been used since the 19^th century as a fungicide for grapes and other crops. Organic growers’ associations consider Bordeaux acceptable for use in organic food production. For non-occupationally exposed humans, oral intake is the major source of copper exposure (WHO 1998).

Copper is an essential element. Enzymes containing copper are important for the body to transport and use iron (WHO 1996). Anaemia is therefore one of the first symptoms of copper deficiency. Copper deficiency, however, is not common (WHO 1998), as copper is widely distributed in food, particularly in meat, liver, kidney, heart and other forms of offal, fish and green vegetables.

Copper is stored in the liver, heart, brain, kidneys and muscles.

In 1996, a joint FAO/International Atomic Energy Agency/WHO expert consultation set an upper limit for the safe range of population mean exposures for adults of 0.2 mg/kg bw/day (WHO 1996). This value has been used as the tolerable limit for the purposes of dietary modelling and was also used during the review of the Food Standards Code (ANZFA 1999).

The mean, median, maximum and minimum levels of copper in foods are given in Part 2 (Table 12) of the Supplementary Information (FSANZ 2002). The estimated dietary exposures to copper for each age–gender category are given in Appendix 1.

All estimated mean dietary exposures to copper are within acceptable health standards. Because of their high food consumption relative to body weight, the highest mean exposure to copper was for infants, calculated at 32% of the tolerable limit. A range has not been presented for copper because a specific amount of copper was reported for almost all samples and so minimal allowance had to be made for results reported as containing ‘less than the LOR’.

Lead

Lead is a widely distributed metal, although lead concentrations are low in environments where there has been little human activity. Lead has been used for centuries because it is easily extracted from its ores. Lead is used for a number of industrial, domestic and rural purposes—for example, in lead batteries and in leaded petrol (WHO 2000b).

A significant source of exposure to lead is via the diet (Friberg et al. 1979, WHO 2000b). Lead can be unintentionally added to food during processing. Canned foods can be a source of lead, if lead solder has been used in the can seam. However, most cans now in use in Australia have welded seams. In addition, the level of lead in food has been falling due to technological improvements in food manufacturing.

Lead is a cumulative toxin that can primarily affect the blood, nervous system and kidneys. In the blood at high concentrations, lead inhibits red blood cell formation and eventually results in anaemia (WHO 2000b). The effects of high concentrations of lead on the nervous system can vary from hyperactive behaviour and mental retardation to seizures and cerebral palsy. As the kidneys are the primary route for lead excretion, lead tends to accumulate in these organs, causing irreversible damage.

Infants and children are considered particularly vulnerable to lead exposure. This is due to their higher energy requirements, their higher fluid, air and food intake per unit of body weight, and the immaturity of their kidneys, liver, nervous and immune systems. In addition, their rapid body growth, their different body composition and the development of their organs and tissues, in particular the brain, may increase their lead absorption. Behavioural characteristics of infants and children, such as the sucking of hands and other objects and the ingestion of non-food items (pica) may also result in a higher exposure to lead compared with adults. Dietary lead is not the only source of lead exposure. In particular, other important sources of exposure for infants and children to lead are from lead paint, soil and dust (Friberg et al. 1979).

The tolerable limit for lead, maintained at the 53^rd meeting of the Joint FAO/WHO Expert Committee on Food Additives, is 25 µg/kg bw/week (WHO 2000a).

The mean, median, maximum and minimum levels of lead in foods are given in Part 2 (Table 13) of the Supplementary Information (FSANZ 2002). Estimated dietary exposures to lead for each age–gender category are given in Appendix 1.

All estimated mean dietary exposures to lead were below the tolerable limit of 25 µg/kg bw/week and therefore are within acceptable safety standards. The highest mean exposure to lead was for infants because of their high food consumption relative to body weight. The estimated infant exposure to lead ranged from 1% to 33% of the tolerable limit. This range results from limitations of the analytical method, which measured lead down to 0.01 mg/kg, and the significant proportion of results reported as ‘less than the LOR’.

Mercury

Mercury is found naturally in the environment. It is usually found concentrated only in certain areas, geographically known as mercuriferous belts. Apart from industrial activities, mercury is also released into the environment during earthquakes and volcanic activity (WHO 1989a).

Mercury is found in various forms (elemental, inorganic and organic), all of which have different toxicological properties. The most toxic to humans is the organic form, with the most common organic form being methyl mercury. Methyl mercury is largely produced from the methylation of inorganic mercury by microbial activity (WHO 1989b). This is most likely to occur in marine and freshwater sediments. Methyl mercury is rapidly taken up and concentrated by filter-feeding organisms upon which fish feed.

In general, the diet is the major source of exposure to mercury, with seafood containing much higher levels of mercury than most other foods.

The tolerable limit for total mercury, set at the 16th meeting of the Joint FAO/WHO Expert Committee on Food Additives and maintained after reconsideration at the 22^nd meeting of the same committee, is 0.3 mg per person per week, equivalent to 5 µg/kg bw/week (WHO 1989b).

In this survey, total mercury, which included both organic and inorganic mercury, was measured in all foods. Mercury (total) was detected in all of the seafood samples. Low levels of organic mercury were found in canned tuna and fish portions. No organic mercury was detected in fish fillets and prawns. The mean, median, maximum, and minimum levels of total mercury and organic mercury in foods are given in Part 2 (Tables 14 and 15 respectively) of the Supplementary Information (FSANZ 2002). Seafood was shown to be the greatest source of mercury in all the diets for all age–gender categories. Of the foods analysed, fish portions had the highest level of mercury. Estimated dietary exposures to mercury for all age–gender categories are given in Appendix 1.

In the 20^th ATDS, the estimated mean dietary exposures to mercury for all age-gender groups were below the tolerable limit. Because of their high food consumption relative to body weight, the highest mean exposure to mercury was for infants, where the exposure ranged from 1% up to 35% of the tolerable limit. This range results from limitations of the analytical method, which measured mercury down to 0.002 mg/kg, and the high proportion of samples reported as containing ‘less than the LOR’.

In the 19^th ATDS, a wider range was reported for dietary exposures to mercury and, for some age-gender categories, this range extended above the acceptable health standard. Refinements to the analytical methods and consequent lower limits of reporting for mercury in the 20^th survey have meant that a more refined dietary exposure estimate for mercury has been achieved. The refinements have established that the dietary exposures to mercury for all age-gender categories are within acceptable health standards.

In the ANZFA review of Volume 1 of the Food Standards Code (1998-2000) , more comprehensive data on mercury levels in food were available than in the 19^th ATDS. Estimated dietary exposures to mercury were lower than reference health standards for the general population. There was, however, cause for concern about the potential exposure to mercury for pregnant women consuming large amounts of fish with high mercury levels, because of the sensitivity of the foetus to mercury. As a result of the review, ANZFA developed an advisory statement for pregnant women on mercury in fish, in consultation with health professionals and the fishing industry. This advisory statement (Mercury In Fish: Advisory Statement for Pregnant Women) is available on the Food Standards Australia New Zealand website (FSANZ 2002).

Selenium

Selenium is essential to humans at low levels but potentially toxic at high levels of exposure. Selenium is widely distributed in rocks and soils; however, its distribution is uneven.

Selenium was known as a toxicant before being recognised as a nutrient. At high levels of exposure, it may produce symptoms associated with changes in nail pathology and hair loss. Selenium is also essential to humans, in that it helps maintain cell membrane integrity and has an antioxidant role in the body. Selenium deficiency can lead to diseases such as Keshan disease and Kaschin-Beck disease. Both diseases have been reported in selenium-deficient areas, such as parts of China (ANZFA 1999).

The Australian Recommended Dietary Intake (RDI) for selenium for different sub-populations was set by the NHMRC in 1987. The RDIs are 85 µg/day (1.04 µg/kg bw/day) for adult males; 70 µg/day (1.06 µg/kg bw/day) for adult females; 85 µg/day (1.73 µg/kg bw/day) for boys; 70 µg/day (1.35 µg/kg bw/day) for girls; 25 µg/day (1.79 µg/kg bw/day) for toddlers; and 15 µg/day (1.63 µg/kg bw/day) for infants (NHMRC 2001b), based on the body weights for these age groups given in Part 1 (Table 4) of the supplementary section (FSANZ 2002).

As yet, the WHO has made no recommendation regarding tolerable limits of selenium (WHO 1987a). Based on limited human data, the biochemical changes (reduction in the ratio of plasma selenium levels to erythrocyte selenium) linked with exposure of humans to selenium at 750 µg/day is interpreted to represent the first indicator of chronic selenium toxicity and therefore is a Lowest Observable Effect Level (LOEL). A No Observable Effect Level (NOEL) could not be set from human data but is assumed to lie close to the LOEL. Traditionally, the exposure limit for toxicity is determined by dividing the NOEL by a series of uncertainty factors, depending on the level of uncertainty in the information used to determine the NOEL. However, since selenium is an essential element, it requires a different approach for the estimation of maximum tolerable intake levels. This is because there are two ranges of intakes associated with adverse health effects: excessive intake and inadequate levels, both of which may result in illness. It is therefore not usual to use uncertainty factors in the determination of the tolerable intake levels for essential elements because division of the NOEL (in this case a LOEL) could produce a recommended level which, if followed, could result in deficiency of that element. Chronic selenium intake of 750 µg/day is proposed as the tolerable limit for selenium. This corresponds to an intake of 12.5 µg/kg bw/day for adults, assuming a 60 kg adult body weight. This level was used in the ANZFA review of the Food Standards Code and in the 19^th ATDS for dietary modelling purposes (ANZFA 1999). This tolerable limit has also been used for dietary modelling purposes in the 20^th ATDS.

The mean, median, maximum and minimum levels of selenium in foods are given in Part 2 (Table 16) of the Supplementary Information (FSANZ 2002). Estimated dietary exposure to selenium for all age–gender categories are given in Appendix 1.

All estimated mean dietary exposures to selenium were below the tolerable limit of 12.5 µg/kg bw/day. Because of their high food consumption relative to body weight, the highest mean exposure to selenium was for two-year-olds, where this exposure ranged from 21% to 24% of the tolerable limit.

All estimated mean intakes of selenium for all age–gender categories are below the suggested tolerable limit of 12.5 µg/kg bw/day. Dietary exposures to selenium are within acceptable health standards.

Estimated dietary exposures to selenium were in the same range as the RDI for each age–gender group (see Table 2). The lower dietary exposure estimates (based on zero values for non-detect results) were lower than the RDI for female adults, boys and girls but exceeded the RDI for male adults, infants and toddlers. The higher dietary exposure estimate (based on LOR numerical values for non-detect results) exceeded the RDI in all cases, except for boys and girls aged 12 years. However, since RDIs are established so that the nutrient requirements of virtually all the population are met, it is likely that actual requirements for selenium will be met for most people in these age groups.

Table 2: Mean estimated dietary exposures to selenium compared with the Recommended Dietary Intake (RDI)

Adult males; Adult females Boys Toddlers 25–34 years 25–34 years 12 years 12 years 2 years 9 months
µg/kg bw/day µg/kg bw/day µg/kg bw/day µg/kg bw/day µg/kg bw/day µg/kg bw/day

RDI* 1.04 1.06 1.73 1.35 1.79 1.63

Mean
Dietary exposure 1.17–1.41 0.96–1.18 1.48-1.66 1.14–1.31 2.61–3.0 2.14-2.41

* RDI expressed per kilogram body weight for each age–gender group (NHMRC 2001b).

Tin

Tin is a metal that has been used since ancient times as an alloy in combination with copper to produce bronze. Today tin is used in plating, solders and alloys.

The main route of exposure to tin is through food, although l