Urinary arsenic concentrations and speciation in Cornwall residents L.R. Johnson and J.G. Farmer 1 Department of Forensic Medicine and Science, Universityof Glasgow, Glasgow G12 8QQ, Scotland
Abstract
Inorganic arsenic and its methylated metabolites were determined in urine from adults and children in Cornwall and from corresponding control groups in Glasgow. In the mineralised south-west of England, where it has been suggested that the highly enriched soil arsenic concentrations may at least be a cofactor in the increased incidence of skin cancer, urinary arsenic levels were, in general, only slightly elevated. The potential for increased intake of inorganic arsenic in Cornwall was, however, reflected in the more frequent occurrence of trivalent inorganic arsenic and monomethylarsonic acid in urine and, of especial significance, in two comparatively highly elevated sum of arsenic species concentrations of 48.7 and 20.8 t.tg g-1 creatinine recorded for two pre-school children. These findings are discussed with reference to recommended limits and pathways of exposure to inorganic arsenic.
Introduction
The toxicity of arsenic depends upon its chemical form (WHO, 1981; Squibb and Fowler, 1983; Zielhuis and Wibowo, 1984). For example, comparatively small quantifies of inorganic arsenic, especially in the trivalent form, can be detrimental to health. In contrast, no harmful effects have been attributed to arsenobetaine, (CH3)3As+CH2COOH, the organoarsenical whose presence in fish and shellfish constitutes the major source of dietary arsenic. Accordingly, the former FAO/WHO maximum acceptable daily intake of total arsenic of 50 ~tg kg-1 body weight has been replaced by a provisional tolerable daily intake, specifying inorganic arsenic, of just 2 ~g kg1 body weight (WHO, 1983). Ingestion of inorganic arsenic can result in a variety of dose- related effects, ranging from death in acute poisoning episodes to chronic diseases resulting from long-term low-level occupational or environmental exposure. Examples of the latter include skin pigmentation changes and keratosis, skin cancer, gastrointestinal disturbances, peripheral vascular disorders and neurological disease found in association with the consumption of drinking water of naturally elevated inorganic arsenic concentration (typically 0.4 - 1.0 mg L 1 in areas of Chile (Borgono et al., 1977), Mexico (Cebrian et al., 1985) and Taiwan (Tseng, 1977; Linet al., 1985). The potentially most susceptible region of the UK is the highly mineralised south-west of England, especially Cornwall, where mining and smelting of arsenical and associated metalliferous ores during the latter part of the nineteenth century have led to widespread inorganic I Author to whom correspondence should be addressed. Present address: Deparmaent of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, Scotland.
arsenic contamination of stream sediments, agricultural soils, garden soils and housedusts (Culbard and Johnson, 1984; Thornton and Abrahams, 1984; Xu and Thornton, 1985). It has been suggested that local exposure to arsenic may be at least partially responsible for the increased incidence of malignant melanoma in Cornwall (Clough !980, Philipp et al., 1984). In this pilot study, it was decided to investigate the arsenic exposure of individuals from high-arsenic areas of Cornwall via the determination of the individual species of inorganic arsenic (pentavalent, As(V); trivalent, As(III)) and its metabolites (monomethylarsonic acid, MMAA, CH3AsO(OH)2; dimethylarsinic acid, DMAA, (CH3)2AsO(OH)) in urine, the major route of excretion (Vahter, 1983). In this way, the influence of contributions to total urinary arsenic from inert dietary organoarsenicals, which are excreted unchanged (Luten et al., 1982), can largely be excluded. For comparison purposes, a control group from Glasgow in the west of Scotland, unexposed to inorganic arsenic other than to the small amounts present in the typical UK diet, was also studied. Methods
Complete first-void urine samples were collected in polypropylene bottles from 37 Cornwall residents living in areas predominantly in the Camborne/Redruth district, previously identified as having high concentrations of arsenic in soils and housedusts (Culbard and Johnson, 1984). Of the 37 people, 28 (16 male, 12 female) were classified for the purposes of this study as adults (i.e. > 8 years old) and 9 (5 male, 4 female) as children (i.e. < 8 years old). A division at 8 years of age was made as it was considered that any child older than this would probably not indulge in the characteristic "hand-to-mouth" activity
40
Urinary arsenic concentrations Table 1 Typical results from an intercomparison exercise for the determination of the concentrations (gg L "l) of arsenic species in urine.
Sample
As(V)
As(Ill)
MMAA
DMAA
Sum
1 This work HSE*
--).
Figure 2 Sum of arsenic speciles (As(V), As(Ill), MMAA, DMAA) concentrations (~tg g creatinine) in the urine of adults and children from Glasgow and Cornwall. The geometric mean for each data set is shown by the broken line (--->--).
of the Cornwall samples. Consequently, it was in just 32% of the urine samples from the south-west that DMAA (1.0 - 33.5 ~g L -1) was the only species detected. Nonetheless, DMAA remained the predominant species, averaging 84% of the sum. Individual results for the sum of As(V), As(III), MMAA and DMAA are displayed for Glasgow adults, Cornwall adults Glasgow children and Cornwall children in Figure 1 (,ug L "l) and Figure 2 ~ g g-1 creatinine). Of the control groups, 78% excreted less than 10 ~tg L "1 (80% < 10 ~tg g-l) while the corresponding, values for the Cornwall groups were 62% (< 10 lxg L ) and 76% (< 10 ~tg g-l). There is a marked skew of the data to the left of a normal distribution. The data are in fact log-normally distributed. Consequently, the summaries of Table 2 ~ g L I ) and Table 3 (l.tg g-1 creatinine) include the more useful geometric mean and standard deviation as well as the arithmetic mean and standard deviation. All subsequent statistical tests used in the comparison of the control and Cornwall groups are based on the geometric means and standard deviations of Table 3 ~ g g-l) derived from the logarithmically transformed data.
The importance of distinguishing analytically between the four species (As(V), As(III), MMAA and DMAA) and total urinary arsenic, which includes seafood organoarsenicals, is illustrated by the differences between the respective geometric means ~ g g I) of 5.0 (sum) and 25.4 (total) for Glasgow conlxol samples and 7.0 (sum) and 23.7 (total) for Cornwall samples. Discussion
The predominance of DMAA in human urine has been reported for other population groups and also in metabolic studies, where the biotransformation of administered inorganic arsenic to less toxic products via the reduction/methylation pathway - As(V) --> As(III) --> MMAA --> DMAA - is considered to be a natural detoxification mechanism (Vahter, 1983). Consideration of this pathway suggests that the more frequent occurrence and higher levels of As(III) and MMAA in the urine of Cornwall residents, compared with Glasgow controls, reflect greater human exposure to inorganic arsenic in Cornwall. Statistical analysis of the logarithmically transformed data, using Student's t test, shows that there is
42
Urinary arsenic concentrations Table 2 Summary of the sum concentrations (~tg L "l) of urinary arsenic species (As(V), As(Ill), MMAA and DMAA) excreted by Glasgow control groups and Cornwall residents.
Category
n
Range
AM _+ISD
GM
GSD
Glasgow adults Glasgow children
40 10
1.0 - 30.0 2.3 - 19.6
6.6 + 5.7 10.1 + 6.1
5.1 8.1
2.1 2.1
Cornwall adults Cornwall children
28 9
1.7 - 23.7 2.5 - 39.9
9.1 + 6.9 11.1 +_11.8
6.6 7.9
2.4 2.3
AM, arithmetic mean; GM, geometric mean; SD, standard deviation; GSD, geometric standard deviation. In summation, individual arsenic species concentrations of less than 0.5 lxg L -1, the detection limit, were taken as 0 p.g L -1. a statistically significant difference between the mean sum of arsenic species eliminated by the adults of the Cornwall (6.1 lxg g-i) and Glasgow (4.4 lxg g-l) groups, but only at the 5% significance level. Although there is a significant difference, at the 2% level, between the mean arsenic concentrations for adults and children for both Cornwall residents (6.1 I.tg g-l; 10.8 l-tg gq) and Glasgow controls (4.4 ~tg g-l; 8.6 ~tg g-l) the difference between the children of Cornwall (10.8 ~tg g-l) and Glasgow (8.6 ~tg g-l) is not statistically significant. It must be noted, however, that the data sets for the children are small (n--9), precluding definitive statistical evaluation. In similar studies where the necessary analytical arsenic speciation has been performed, sums of urinary inorganic As, MMAA and DMAA concentrations of 5.9 + 2.9 ~tg L l (arithmetic mean (AM), n=148), 8.2 + 2.0 [tg g-l (GM, n=99) and 9 I~g L l (AM, n=203) have been reported for reference adult populations, subject to "normal" environmental exposure to inorganic arsenic, from Italy (Foa et al., 1984), Sweden (Vahter and Lind, 1986) and East Germany (Stoeppler and Apel, 1984) respectively. That both the Glasgow control and Cornwall data (Tables 2 and 3) are clearly in line with these figures for "normally" exposed individuals is emphasised by the dramatically enhanced urinary arsenic concentrations
found in regions of the world where significant environmental exposure to inorganic arsenic has been associated with observable health effects. For example. mean urinary arsenic concentrations of 75.7 • 39.1 ~tg L "~ and 201 + 58 lxg L q have been linked with a number of cases of blackfoot disease and Bowen's disease in an area of Taiwan supplied by artesian well waters of typical arsenic concentration 0.4 - 0.6 mg L 1 (Tseng, 1977; Lin et al., 1985) and a mean urinary level of 422_+ 269 ~tg g-1 has been associated with cutaneous signs of chronic arsenic poisoning in North Mexican inhabitants subject to exposure via the consumption of drinking water of average arsenic concentration 0.41 mg L -1 (Cebrian et al., 1985). In separate occupational exposure studies, concentrations up to 328 [tg g-1 (GM 79 lxg g,1) and 956 ~tg g-1 (GM 245 ~tg g-l) have been found for the sum of inorganic As, MMAA and DMAA in urine from smelter (Vahter et a/., 1986) and chemical manufacturing workers (Farmer and Johnson, in preparation) exposed to inorganic arsenic compounds. It is known from metabolic studies that 40 - 60% of the daily intake of inorganic arsenic is excreted each day 9in urine (Buchet et al., 1981; Johnson and Farmer, in preparation). Therefore the mean urinary arsenic concentrations for the Glasgow and Cornwall groups (Table 3) can be related to the mean daily intake of
Table 3 Summary of the sum concentrations (~tg g-1 creatinine) of urinary arsenic species (As(V), As(Ill), MMAA and DMAA) excreted by Glasgow control groups and Cornwall residents.
Category
n
Range
AM +ISD
GM
GSD
Glasgow adults Glasgow children
40 9
1.2 - 39.0 2.5 - 19.4
5.8 + 6.2 10.2 + 5.9
4.4 8.6
2.0 1.9
Cornwall adults Cornwall children
28 9
1.8 - 11.2 5.1 - 48.7
6.7 +_2.7 14.3 +13.8
6.1 10.8
1.6 2.!
The sum of arsenic species concentration for each adult and child was calculated in ~tg g-1 creatinine from the corresponding sum in ~tg L -1 and the measured creatinine concentration (g LI). The creatinine concentration was not available for one Glasgow child.
L2~. Johnson and J.G. Farmer
inorganic arsenic, using average daily creatinine output figures of 1.5 g for adults (equivalent to 1.5 L urine at a creatinine concentration of 1 g L "1) and 0.75 g for children. For Glasgow adults, the calculated average daily intake of inorganic arsenic is 11.0 - 16.5 ~tg, comparable to the estimate of 22 lag day-1 which can be derived from the MAFF (1982) value for the average dietary intake of total arsenic of 89 lag day"l, to which seafood contributes 75%, almost exclusively in the form of inert organoarsenicals. The Glasgow control intake of inorganic arsenic is thus well below the 150 lag day "1 considered potentially responsible by The Committee on the Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) (MAFF, 1984) for signs of arsenicism in some individuals. While the same conclusion would be drawn for Glasgow adults from a consideration of the FAO/WHO provisional tolerable daily intake of 2 lag inorganic arsenic per kg body weight (WHO, 1983), the calculated average daily intake of 10.8 - 16.1 lag for children is closer to the tolerable intake of 30 ~tg day'l for a typical 3-year old child of 15 kg weight. For the Cornwall residents of this study, the calculated additional average daily intake of inorganic arsenic is 4.25 - 6.4 lag for adults and 2.75 - 4.1 lag for children, surprisingly low increments in view of the arsenic- contaminated environment in which they live. Despite garden soil arsenic concentrations of up to 1,130 mg kg "l in the Carnborne area (Culbard and Johnson, 1984), well above typical levels of < 40 mg kg"1 elsewhere CLlre and Berrow, 1982), the arsenic content of allotment vegetables is usually well below the UK statutory limit of 1 mg kg -1 fresh weight (Xu and Thornton, 1985; Johnson 1986). Arsenic in Cornish drinking water, as elsewhere in the UK, rarely exceeds 10 lag L "l (MAFF 1982). Increased intake of arsenic by grazing animals, via consumption of contaminated pasture herbage or direct ingestion of soils, could present a possible route for additional exposure of the human population to arsenic in Cornwall (Thornton, 1984). The group perhaps most at risk from contaminated soils, however, is that of young children, who have a habit of sucking dirty fingers and foreign objects. The contribution of lead-contaminated soil and dust to the body lead burden of young children has been the subject of much speculation and investigation in recent years (Duggan, 1983). Although more sophisticated approaches are under investigation (Duggan et al., 1985), estimates of the amount of soil or dust ingested via h.and-to,mouth activity by children range from 10 - 100 mg dayq (Lepow et al., 1974; Duggan and Williams, 1977 I. With a mean soil arsenic concentration of 424 mg kg" in Camborne/Hayle (Culbard and Johnson, 1984) and 10 mg soil consumption, it is possible that a child could be subjected to a soil arsenic intake of 4.21lag day "1, close to the extra intake of 2.75 4.1 lxg day" calculated from the urinary data. At an ingestion level of 100 mg soil of maximum arsenic concentration of 1,130 mg kg 1, the theoretical additional intake could be as high as 113 lag day "l , broadly in line with the maximum range of 60 - 91 lag day q intake of inorganic arsenic calculated from the data for the child (3-year old) with the highest urinary arsenic concentration. Housedust arsenic concentrations of up to 330 mg kg "1
43
(Culbard and Johnson, 1984) may also represent a potentially significant source of inorganic arsenic for very young children, who spend a considerable part of their time within the home environment. Thus, while it appears that the slight differences between Glasgow and mineralised Cornwall in average urinary arsenic concentrations and inorganic arsenic intakes for adults and children are of no real significance, the elevated arsenic levels excreted by two pre-school children, with their lower tolerable daily intake when body weight is taken into account, warrant more extensive investigation. At the time of sampling, these two children lived in the Brea district, in sight of a working tin mine. The opportunity to determine the concentrations and speciation of arsenic in the urine of tin miners would clearly be worthwhile but was unfortunately denied to us in our initial investigation.
Acknowledgements We thank Mr J.A. Cadman and staff of Kerr/er District Council whose assistance and cooperation made the sampling programme possible. Messrs N.J. Smith and B.S. Chana of the Health and Safety Executive, London, cooperated most obligingly in the intercomparison exercise on urinary arsenic speciation. Dr T.D.B. Lyon, Department of Biochemistry, Glasgow Royal Infirmary, kindly supplied the urinary creatinine data. The partial financial support by NERC of LRJ's research studentship is gratefully acknowledged.
References Botgono, J.M., Vicent, P., Venturino, H. and Infante, A. 1977. Arsenic in the drinking water of the city of Antofagasta: r and clinical study before and after the installation of a treatment plant. Envir. Health Perspeet., 19, 103-105, Buchet, J.P., Lauwerys, R. and Roels, H. 1981. Urinary excretion of inorganic arsealic and its metabolites after repeated ingestion of sodium metaarseniteby volunteers.Int.Arch. Occupat. Envir. Health, 48, 111-118.
Cebrian, M.E,, Albores,A., Olguin, A. and Jauge, P. 1985. Risk estimation and exposure assessment in a population chronically exposed to arsenic. In: Pro,:. Fifth International Conference on Heavy Metals in the Environment, Vol. 2, pp.4-6. CEP Consultants,Edinburgh. Clongh, P. 1980. Incidence of malignant melanoma of the skin in England and Wales. Br. Med. J.,I, 112.
Chana, B.S. and Smith, N.L 1987. Urinary arsenicspcciationby high-performanceliquidchr~natography/atornicabsorption spectrometry for monitoring occupational exposure to inorganic arsenic. Analyt. Chim. Acta, 197, 177-186. Culbard, E.B. and Johnson, L.R. 1984. An assessmem of arsenic in honsedust and garden soils from south-west England and their implications for human health, In: Environmental Contamination, pp.276-281. CEP Consultants, Edinburgh. Duggan, M.L 1983. Lead in dust as a source of children's t~dy lead. In: Rutter, M. and Jones, R.R. (eds.), Lead versus Health pp. 115-139. Wiley, Chichester. Duggan, M.L and Williams, S. 1977. Lead-in-dust in city streets. Sci. Tot. Envir., 7, 91-97. Duggan, MJ., hskip, M.L Rundle. S.A. and Moorcroft, LS. 1985. Lead in playground dust and on the hands of schoolchildren. Sci. Tot. Envir., 44, 65-79, Foa, V., Culombi, A., Maroni, M., Buratti, M. and Calzaferri, G. 1984. The spaciation of the chemical forms of arsenic in the
44
Urinary arsenic concentrations
biological monitoring of exposure to inorganic arsenic. Sci. Tot. Envir., 34, 241-259. Grabinski, A.A. 1981. Determination of arsenic (11I), arsenic (V), monomethylarsonate and dimethylarsinate by ion-exchange chromatography with flameless atomic absorption spectrometric detection. Analyt. Chem., 53, 966-968. Johnson, L.R. 1986. The Chemical Speciation and Transformations of Arsenic in Humans and in the Environment. PhD Thesis, University of Glasgow. 448 pp. Lepow, M.L., Bruchman, L., Rubino, R.A., Markowitz, S., Gillette, M. and Kapish, I. 1974. Role of airborne lead in increased body burden of lead in Hartford children. Envir. ltealth Perspect., 7, 99-102. Lin, S.M., Chiang, C.H. and Yang, M.H. 1985. Arsenic concentration in the urine of patients with blackfoot disease and Bowen's disease. Biol. Trace Element Res., 8, 11-18. Love]a, M.A. and Farmer, J.G. 1985. Arsenic speciation in urine from humans intoxicated by inorganic arsanie compounds. Hum. Toxicol., 4, 203-214. Luten, J.B,, Riekwell-Booy, G. and Rauchbaar, A. 1982. Occurrence of arsenic in plaice (Pleuronectes platessa), nature of organoarsenic compound present and its excretion by man. Envir. Health Perspect., 45, 165-170. Ministry of Agriculture, Fisheries and Food. t982. The Eighth Report of the Steering Group on Food Surveillance. The Working Party on the Monitoring of Foodstuffs for Heavy Metals. Survey of Arsenic in Food. Food Surveillance Paper No. 8, 36pp. HMSO, London. Ministry of Agriculture, Fisheries and Food. 1984. Food Additives and Contaminants Comrnittce Report on the Review of the Arsenic in Food Regulations. FAC/REP/39, 29pp. HMSO, London. Philipp, R., Hughes, A.O., Robertson, M.C. and Mitchell, T.F. 1984. Soil levels of arsenic and malignant melanoma incidence. In: Environmental Contamination, pp. 432-437. CEP Consultants, Edinburgh. Squibb, K.S. and Fowler, B.A. 1983. The toxicity of arsenic and its compounds. In: B.A. Fowler (ed.), Biological and Environmental Effects of Arsenic, pp.233-269. Elsevier, Amsterdam. Stoeppler, M. and Apel, M. 1984. Determination of arsenic species in liquid and solid materials from the environment and food, and
in body fluids. Fresenius' Zeitschr~ft flit Analytische Chemie, 317, 226-227. Thornton, I. 1984. Contamination of land by metalliferous nrning wastes in the U.K.: implication to agriculture and human health. In: Environmental Contamination, pp.474-481. CEP Consultants, Edinburgh. Thornton, L and Abrahams, P. 1984. Historical records of metal pollution in the environment. La: Nriagu, J.O. (ed.), Changing Metal Cycles and Human Health pp.7-25. Springer-Verlag, Berlin. Tseng, W.-P. 1977. Effects and dose-response relationships of skin cancer and blackfoot disease with arsenic. Envir. Health Perspect., 19, 109-119. Ure, A.M. and Berrow, M.L 1982. The elemental constituents of soils. In: Environmental Chemistry, VoL 2, pp.94-204. Royal Society of Chemistry, London. Vahter, M. 1983. Metabolism of arsenic. In: Fowler, B.A. (ed.), Biological and Environmental Effects of Arsenic, pp.171-198. Elsevier, Amsterdam, Vahter, M. and Lind, B. 1986. Concentrations of arsenic in urine of the general population in Sweden. Sei. Tot. EnvY'., 54~ 1-12. Vahter, M., Friberg, L., Rahnster, t3., Nygren, 7~. and Nolinder, P. 1986. Airborne arsenic and urinary excretion of rnetabolites of inorganic arsenic among smelter workers, tnt. Arch. Occup. Envir. Health, 57, 79-91. World Health Organization. 1981. Environmental Health Criteria 18: Arsenic, 174pp. World Health Organization, Geneva. World Health Organization. 1983.27th Report of the Joint FAOIWHO Expert Committee on Food Additives, p.29. Technical Report Series 696, World Health Organization, Geneva, Xu, J. and Thornton, I. 1985. Arsenic in garden soil,zand vegetable crops in Cornwall, England: implications for human health. Env. Geochem. Health, 7, 131-133. Zielhuis, R.L. and Wibowo, A.AoE. 1984. Standard setting and metal speeiation: arsenic. In: Nriagu, J.O~ (ed.), Changing Metal Cycles and Human Health pp.323-344. Sprir~ger-Vedag,Berlin. (Manuscript No. 174: received June 7, 1988 and accepted alter revision November 24, 1988.)
Abstract
Inorganic arsenic and its methylated metabolites were determined in urine from adults and children in Cornwall and from corresponding control groups in Glasgow. In the mineralised south-west of England, where it has been suggested that the highly enriched soil arsenic concentrations may at least be a cofactor in the increased incidence of skin cancer, urinary arsenic levels were, in general, only slightly elevated. The potential for increased intake of inorganic arsenic in Cornwall was, however, reflected in the more frequent occurrence of trivalent inorganic arsenic and monomethylarsonic acid in urine and, of especial significance, in two comparatively highly elevated sum of arsenic species concentrations of 48.7 and 20.8 t.tg g-1 creatinine recorded for two pre-school children. These findings are discussed with reference to recommended limits and pathways of exposure to inorganic arsenic.
Introduction
The toxicity of arsenic depends upon its chemical form (WHO, 1981; Squibb and Fowler, 1983; Zielhuis and Wibowo, 1984). For example, comparatively small quantifies of inorganic arsenic, especially in the trivalent form, can be detrimental to health. In contrast, no harmful effects have been attributed to arsenobetaine, (CH3)3As+CH2COOH, the organoarsenical whose presence in fish and shellfish constitutes the major source of dietary arsenic. Accordingly, the former FAO/WHO maximum acceptable daily intake of total arsenic of 50 ~tg kg-1 body weight has been replaced by a provisional tolerable daily intake, specifying inorganic arsenic, of just 2 ~g kg1 body weight (WHO, 1983). Ingestion of inorganic arsenic can result in a variety of dose- related effects, ranging from death in acute poisoning episodes to chronic diseases resulting from long-term low-level occupational or environmental exposure. Examples of the latter include skin pigmentation changes and keratosis, skin cancer, gastrointestinal disturbances, peripheral vascular disorders and neurological disease found in association with the consumption of drinking water of naturally elevated inorganic arsenic concentration (typically 0.4 - 1.0 mg L 1 in areas of Chile (Borgono et al., 1977), Mexico (Cebrian et al., 1985) and Taiwan (Tseng, 1977; Linet al., 1985). The potentially most susceptible region of the UK is the highly mineralised south-west of England, especially Cornwall, where mining and smelting of arsenical and associated metalliferous ores during the latter part of the nineteenth century have led to widespread inorganic I Author to whom correspondence should be addressed. Present address: Deparmaent of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, Scotland.
arsenic contamination of stream sediments, agricultural soils, garden soils and housedusts (Culbard and Johnson, 1984; Thornton and Abrahams, 1984; Xu and Thornton, 1985). It has been suggested that local exposure to arsenic may be at least partially responsible for the increased incidence of malignant melanoma in Cornwall (Clough !980, Philipp et al., 1984). In this pilot study, it was decided to investigate the arsenic exposure of individuals from high-arsenic areas of Cornwall via the determination of the individual species of inorganic arsenic (pentavalent, As(V); trivalent, As(III)) and its metabolites (monomethylarsonic acid, MMAA, CH3AsO(OH)2; dimethylarsinic acid, DMAA, (CH3)2AsO(OH)) in urine, the major route of excretion (Vahter, 1983). In this way, the influence of contributions to total urinary arsenic from inert dietary organoarsenicals, which are excreted unchanged (Luten et al., 1982), can largely be excluded. For comparison purposes, a control group from Glasgow in the west of Scotland, unexposed to inorganic arsenic other than to the small amounts present in the typical UK diet, was also studied. Methods
Complete first-void urine samples were collected in polypropylene bottles from 37 Cornwall residents living in areas predominantly in the Camborne/Redruth district, previously identified as having high concentrations of arsenic in soils and housedusts (Culbard and Johnson, 1984). Of the 37 people, 28 (16 male, 12 female) were classified for the purposes of this study as adults (i.e. > 8 years old) and 9 (5 male, 4 female) as children (i.e. < 8 years old). A division at 8 years of age was made as it was considered that any child older than this would probably not indulge in the characteristic "hand-to-mouth" activity
40
Urinary arsenic concentrations Table 1 Typical results from an intercomparison exercise for the determination of the concentrations (gg L "l) of arsenic species in urine.
Sample
As(V)
As(Ill)
MMAA
DMAA
Sum
1 This work HSE*
--).
Figure 2 Sum of arsenic speciles (As(V), As(Ill), MMAA, DMAA) concentrations (~tg g creatinine) in the urine of adults and children from Glasgow and Cornwall. The geometric mean for each data set is shown by the broken line (--->--).
of the Cornwall samples. Consequently, it was in just 32% of the urine samples from the south-west that DMAA (1.0 - 33.5 ~g L -1) was the only species detected. Nonetheless, DMAA remained the predominant species, averaging 84% of the sum. Individual results for the sum of As(V), As(III), MMAA and DMAA are displayed for Glasgow adults, Cornwall adults Glasgow children and Cornwall children in Figure 1 (,ug L "l) and Figure 2 ~ g g-1 creatinine). Of the control groups, 78% excreted less than 10 ~tg L "1 (80% < 10 ~tg g-l) while the corresponding, values for the Cornwall groups were 62% (< 10 lxg L ) and 76% (< 10 ~tg g-l). There is a marked skew of the data to the left of a normal distribution. The data are in fact log-normally distributed. Consequently, the summaries of Table 2 ~ g L I ) and Table 3 (l.tg g-1 creatinine) include the more useful geometric mean and standard deviation as well as the arithmetic mean and standard deviation. All subsequent statistical tests used in the comparison of the control and Cornwall groups are based on the geometric means and standard deviations of Table 3 ~ g g-l) derived from the logarithmically transformed data.
The importance of distinguishing analytically between the four species (As(V), As(III), MMAA and DMAA) and total urinary arsenic, which includes seafood organoarsenicals, is illustrated by the differences between the respective geometric means ~ g g I) of 5.0 (sum) and 25.4 (total) for Glasgow conlxol samples and 7.0 (sum) and 23.7 (total) for Cornwall samples. Discussion
The predominance of DMAA in human urine has been reported for other population groups and also in metabolic studies, where the biotransformation of administered inorganic arsenic to less toxic products via the reduction/methylation pathway - As(V) --> As(III) --> MMAA --> DMAA - is considered to be a natural detoxification mechanism (Vahter, 1983). Consideration of this pathway suggests that the more frequent occurrence and higher levels of As(III) and MMAA in the urine of Cornwall residents, compared with Glasgow controls, reflect greater human exposure to inorganic arsenic in Cornwall. Statistical analysis of the logarithmically transformed data, using Student's t test, shows that there is
42
Urinary arsenic concentrations Table 2 Summary of the sum concentrations (~tg L "l) of urinary arsenic species (As(V), As(Ill), MMAA and DMAA) excreted by Glasgow control groups and Cornwall residents.
Category
n
Range
AM _+ISD
GM
GSD
Glasgow adults Glasgow children
40 10
1.0 - 30.0 2.3 - 19.6
6.6 + 5.7 10.1 + 6.1
5.1 8.1
2.1 2.1
Cornwall adults Cornwall children
28 9
1.7 - 23.7 2.5 - 39.9
9.1 + 6.9 11.1 +_11.8
6.6 7.9
2.4 2.3
AM, arithmetic mean; GM, geometric mean; SD, standard deviation; GSD, geometric standard deviation. In summation, individual arsenic species concentrations of less than 0.5 lxg L -1, the detection limit, were taken as 0 p.g L -1. a statistically significant difference between the mean sum of arsenic species eliminated by the adults of the Cornwall (6.1 lxg g-i) and Glasgow (4.4 lxg g-l) groups, but only at the 5% significance level. Although there is a significant difference, at the 2% level, between the mean arsenic concentrations for adults and children for both Cornwall residents (6.1 I.tg g-l; 10.8 l-tg gq) and Glasgow controls (4.4 ~tg g-l; 8.6 ~tg g-l) the difference between the children of Cornwall (10.8 ~tg g-l) and Glasgow (8.6 ~tg g-l) is not statistically significant. It must be noted, however, that the data sets for the children are small (n--9), precluding definitive statistical evaluation. In similar studies where the necessary analytical arsenic speciation has been performed, sums of urinary inorganic As, MMAA and DMAA concentrations of 5.9 + 2.9 ~tg L l (arithmetic mean (AM), n=148), 8.2 + 2.0 [tg g-l (GM, n=99) and 9 I~g L l (AM, n=203) have been reported for reference adult populations, subject to "normal" environmental exposure to inorganic arsenic, from Italy (Foa et al., 1984), Sweden (Vahter and Lind, 1986) and East Germany (Stoeppler and Apel, 1984) respectively. That both the Glasgow control and Cornwall data (Tables 2 and 3) are clearly in line with these figures for "normally" exposed individuals is emphasised by the dramatically enhanced urinary arsenic concentrations
found in regions of the world where significant environmental exposure to inorganic arsenic has been associated with observable health effects. For example. mean urinary arsenic concentrations of 75.7 • 39.1 ~tg L "~ and 201 + 58 lxg L q have been linked with a number of cases of blackfoot disease and Bowen's disease in an area of Taiwan supplied by artesian well waters of typical arsenic concentration 0.4 - 0.6 mg L 1 (Tseng, 1977; Lin et al., 1985) and a mean urinary level of 422_+ 269 ~tg g-1 has been associated with cutaneous signs of chronic arsenic poisoning in North Mexican inhabitants subject to exposure via the consumption of drinking water of average arsenic concentration 0.41 mg L -1 (Cebrian et al., 1985). In separate occupational exposure studies, concentrations up to 328 [tg g-1 (GM 79 lxg g,1) and 956 ~tg g-1 (GM 245 ~tg g-l) have been found for the sum of inorganic As, MMAA and DMAA in urine from smelter (Vahter et a/., 1986) and chemical manufacturing workers (Farmer and Johnson, in preparation) exposed to inorganic arsenic compounds. It is known from metabolic studies that 40 - 60% of the daily intake of inorganic arsenic is excreted each day 9in urine (Buchet et al., 1981; Johnson and Farmer, in preparation). Therefore the mean urinary arsenic concentrations for the Glasgow and Cornwall groups (Table 3) can be related to the mean daily intake of
Table 3 Summary of the sum concentrations (~tg g-1 creatinine) of urinary arsenic species (As(V), As(Ill), MMAA and DMAA) excreted by Glasgow control groups and Cornwall residents.
Category
n
Range
AM +ISD
GM
GSD
Glasgow adults Glasgow children
40 9
1.2 - 39.0 2.5 - 19.4
5.8 + 6.2 10.2 + 5.9
4.4 8.6
2.0 1.9
Cornwall adults Cornwall children
28 9
1.8 - 11.2 5.1 - 48.7
6.7 +_2.7 14.3 +13.8
6.1 10.8
1.6 2.!
The sum of arsenic species concentration for each adult and child was calculated in ~tg g-1 creatinine from the corresponding sum in ~tg L -1 and the measured creatinine concentration (g LI). The creatinine concentration was not available for one Glasgow child.
L2~. Johnson and J.G. Farmer
inorganic arsenic, using average daily creatinine output figures of 1.5 g for adults (equivalent to 1.5 L urine at a creatinine concentration of 1 g L "1) and 0.75 g for children. For Glasgow adults, the calculated average daily intake of inorganic arsenic is 11.0 - 16.5 ~tg, comparable to the estimate of 22 lag day-1 which can be derived from the MAFF (1982) value for the average dietary intake of total arsenic of 89 lag day"l, to which seafood contributes 75%, almost exclusively in the form of inert organoarsenicals. The Glasgow control intake of inorganic arsenic is thus well below the 150 lag day "1 considered potentially responsible by The Committee on the Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) (MAFF, 1984) for signs of arsenicism in some individuals. While the same conclusion would be drawn for Glasgow adults from a consideration of the FAO/WHO provisional tolerable daily intake of 2 lag inorganic arsenic per kg body weight (WHO, 1983), the calculated average daily intake of 10.8 - 16.1 lag for children is closer to the tolerable intake of 30 ~tg day'l for a typical 3-year old child of 15 kg weight. For the Cornwall residents of this study, the calculated additional average daily intake of inorganic arsenic is 4.25 - 6.4 lag for adults and 2.75 - 4.1 lag for children, surprisingly low increments in view of the arsenic- contaminated environment in which they live. Despite garden soil arsenic concentrations of up to 1,130 mg kg "l in the Carnborne area (Culbard and Johnson, 1984), well above typical levels of < 40 mg kg"1 elsewhere CLlre and Berrow, 1982), the arsenic content of allotment vegetables is usually well below the UK statutory limit of 1 mg kg -1 fresh weight (Xu and Thornton, 1985; Johnson 1986). Arsenic in Cornish drinking water, as elsewhere in the UK, rarely exceeds 10 lag L "l (MAFF 1982). Increased intake of arsenic by grazing animals, via consumption of contaminated pasture herbage or direct ingestion of soils, could present a possible route for additional exposure of the human population to arsenic in Cornwall (Thornton, 1984). The group perhaps most at risk from contaminated soils, however, is that of young children, who have a habit of sucking dirty fingers and foreign objects. The contribution of lead-contaminated soil and dust to the body lead burden of young children has been the subject of much speculation and investigation in recent years (Duggan, 1983). Although more sophisticated approaches are under investigation (Duggan et al., 1985), estimates of the amount of soil or dust ingested via h.and-to,mouth activity by children range from 10 - 100 mg dayq (Lepow et al., 1974; Duggan and Williams, 1977 I. With a mean soil arsenic concentration of 424 mg kg" in Camborne/Hayle (Culbard and Johnson, 1984) and 10 mg soil consumption, it is possible that a child could be subjected to a soil arsenic intake of 4.21lag day "1, close to the extra intake of 2.75 4.1 lxg day" calculated from the urinary data. At an ingestion level of 100 mg soil of maximum arsenic concentration of 1,130 mg kg 1, the theoretical additional intake could be as high as 113 lag day "l , broadly in line with the maximum range of 60 - 91 lag day q intake of inorganic arsenic calculated from the data for the child (3-year old) with the highest urinary arsenic concentration. Housedust arsenic concentrations of up to 330 mg kg "1
43
(Culbard and Johnson, 1984) may also represent a potentially significant source of inorganic arsenic for very young children, who spend a considerable part of their time within the home environment. Thus, while it appears that the slight differences between Glasgow and mineralised Cornwall in average urinary arsenic concentrations and inorganic arsenic intakes for adults and children are of no real significance, the elevated arsenic levels excreted by two pre-school children, with their lower tolerable daily intake when body weight is taken into account, warrant more extensive investigation. At the time of sampling, these two children lived in the Brea district, in sight of a working tin mine. The opportunity to determine the concentrations and speciation of arsenic in the urine of tin miners would clearly be worthwhile but was unfortunately denied to us in our initial investigation.
Acknowledgements We thank Mr J.A. Cadman and staff of Kerr/er District Council whose assistance and cooperation made the sampling programme possible. Messrs N.J. Smith and B.S. Chana of the Health and Safety Executive, London, cooperated most obligingly in the intercomparison exercise on urinary arsenic speciation. Dr T.D.B. Lyon, Department of Biochemistry, Glasgow Royal Infirmary, kindly supplied the urinary creatinine data. The partial financial support by NERC of LRJ's research studentship is gratefully acknowledged.
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