Vol. 4: 377-384. Selenium concentration of Finnish foods: Effects of reducing the amount of selenate in fertilizers Ekholm Päivi, Ylinen Maija, Koivistoinen Pekka and Varo Pertti Department ofApplied Chemistry and Microbiology, P.O. Box 27, Viikki D, FIN-00014 University ofHelsinki, Finland The original two supplementation levels of selenium in multinutrient fertilizers (Se 16 and 6 mg kg- 1 fertilizer as sodium selenate; started in 1985) were reduced to one (6 mg kg 1 fertilizer) in 1991. The 16 mg supplementation level was intended for use in cereal production. Due to the lowering of the level of Se application, the Se content of spring cereals (spring wheat, oats and barley) has decreased more than that of any other food in the monitoring programme. The present level, 0.1 mg kg ' for cereal grains, is about 40% of the concentrations common in 1990. The Se concentrations have decreased less in other foods than in cereals. The present Se concentra- tions in milk products, meat and liver are about 70, 60 and 50%, respectively, of the concentrations in 1990. The average daily human Se intake was 0.08 mg day 1 at an energy level of 10 MJ in 1994. Animal protein is the main source of Se. About 40% of the intake comes from meat, 24% from dairy products and eggs, and 11% from fish. Key words: cereals, meat, milk, cheese, eggs, intake ntroduction The general use of selenium(Se)-supplemented fertilizers began in Finland during the 1985 growing season. From then until 1990 two levels of Se supplementation were used in ferti- lizers: 6 mg of Se as sodium selenate per kg in fertilizers used mainly in fodder and hay pro- duction, and 16 mg kg’ 1 in those used in cereal production. A group ofexperts authorized by the Ministry of Agriculture and Forestry evaluated the effects of this measure from 1984 onwards. The results were published as Working Group reports of the Ministry of Agriculture and For- estry, as articles in international scientific jour- nals and as papers at conferences (Ekholm et al. 1990, 1991a, Eurolaetal. 1989, 1990, 1991, Varo et al. 1988). Thereafter the fertilization practice was sim- plified and standardized by lowering the Se level from 16 mg kg’ 1 to 6 mg kg 1 in all fertiliz- ers (Ministry ofAgriculture and Forestry 1990). The new, one-Se-level practice has been in use since the 1991 growing season. Although the range of Se concentrations in foodstuffs had re- © Agricultural Science in Finland Manuscript received December 1994 377 AGRICULTURAL SCIENCE IN EINLAND https://www.c-info.fi/en/info/?token=AJqBMdrDlSCU1Onn.MuNVaLEgz_gm3SqBoCSt9Q.otroVkcuMvAKkemSgmdmgf5-zzeijn6u17A43AatHJpfe970Pni3pXtp6kBC9WqjRvW9rwuGnlRrX9sRneA0B09iwzuxJGDlU8sXU3HLI7c8Y-ovOyRquVhWT5Y41scnpXxOSgAM-5gfwXZaeCMCMYjOSu9e6a6WOziFZ88NtXH5LvDbzMnfIOwvSQpy2mjZf60dAOIb3iZiN6bKD0wd4wMeaQOWUQSSLngTzlxJ-YBk3KFukeeF8rcE-23wvCBMz-fuDtyUMwYigw11XiTNEb2X6Kc8GJeciYqcJb1K7O_PlR4WAq3Q8qG_v6mXFCcocJwMCAo_5OoYAQ Ekholm, P. et al.: Selenium concentration ofFinnish foods mained narrow and safe throughout the supple- mentation period, some Se peak concentrations exceeding 1 mg kg' 1 dry matter had been detect- ed in fodder and hay samples from a few single farms. The high values were most probably caused by liberal use of high-Se fertilizers (16 mg kg 1 ) in the production of grassy feeds and hay. Elimination of these unnecessarily high concentrations was the main reason for lower- ing the Se level of fertilizers. Human intake of Se was already 0.11 mg day 1 in 1987 and was still increasing slightly in the early 19905. None- theless, intake remained consistently very good and acceptable, and concern at the possibility of excessive intake was never expressed by either nutrition or medical experts. On the other hand, a certain amount of public speculation had been aroused by the doubts of some environmental- ists concerning the possible but unverified ef- fects of leached Se on soil, for example, on the algal bloom in Finnish lake waters. This article reports the effects of lowering the Se level in fertilizers on the Se concentra- tions in basic foods and on average Se intake in Finland. Material and methods Sampling The sampling system offoods has remained prin- cipally unchanged throughout the monitoring period (Varo et ai. 1988). Eleven basic foodstuffs were sampled regularly every three months. Pur- chases were made from eight food stores in the Helsinki area. The meat samples were purchased from 16 stores, and the porcine liver samples from a wholesale dealer. The stores were select- ed as being representative of Finland’s major wholesalefood chains. These subsamples give a good overview of the situation countrywide. Sample preparation has been described earlier (Varo et al. 1988). Samples of whole grain wheat and rye were obtained from commercial mills around the country. Each sample (2-5 kg) represented 0.1-5 million kg of grain. The barley and oats samples were chosen from farm samples of the State Grain Storage Center. Each sample repre- sented the harvest of a single farm, and all the Rural Advisory Centres in Finland were covered. Breast milk samples were obtained from Hel- sinki University Central Hospital. Each sample was a pool of milks from several donors (me- dian 20). Analytical method Se was analysed by an electrothermal atomic absorption method for food samples (Kumpu- lainen et al. 1983). The freeze-dried samples were kept overnight at 70°C, and digested in a mixture of concentrated HNO„ HCIO, and3’ 4 H 2S04 . Selenium was reduced to Se IV by 4 M HCI, chelated with ammoniumpyrrolidine dithio- carbamate and then extracted into isobutyl methyl ketone for atomic absorption determina- tion. The accuracy of the method was tested by determining three certified reference materials regularly during the analysis period (Table 1). Three unofficial control materials were analysed continuously as blinds to test the precision of the analytical method. Statistical analyses were performed using SURVO, an integrated environment for Statisti- cal Computingand Related Areas-software. The equality of the means was testedby applying the Kruskal-Wallis test, the non-parametric analy- sis of variance. Results and discussion The effect of redusing the amount of Se in ferti- lizers is seen clearly in the Se concentrations of grains and basic foods (Tables 2 and 3, Figs. 1984 represents the original, unsupplemented Se level common in the early 1980s. In 1990 378 AGRICULTURAL SCIENCE IN FINLAND Vol. 4: 377-384. Table 1. Precision and accuracy of the analytical method for selenium. No. of Mean ± SD Ref. value determina- mgkg IDM mgkg' DM Sample tions Standard reference materials NIST 1577 a Bovine liver 14 0.670 ±0.026 0.71 ±0.07 NIST 1549 Milkpowder 4 o.llo± 0.005 0.110 ±O.OlO BCR 4 0.124± 0.007 0.132 ±O.OlO Wholemeal flour Non-certified control materials Rye flour II 230 0.027 ±0.002 Wheat flour 111 208 0.246 ± 0.009 Milk powder II 102 0.075 ± 0.004 Milk powder 111 72 0.301 ± 0.014 Bovine liver II 84 0.568 ± 0.021 Bovine liver 111 122 0.755 ± 0.030 NIST = National Insitute of Standards & Techology BCR = Community Bureau of Reference the Se concentrations of Finnish agricultural products were reaching their plateaus due to the effect of two-level supplementation started in 1985. The impact of the change to one-level sup- plementation began to emerge in late 1991, which was a transitional year (means not shown in Table 3). The new fertilization practice was affecting all foodstuffs in full by early 1992 (Tables 2 and 3, Figs. 1-4). Se concentrations have declined in all Finn- ish agricultural products since 1991. Milk has been the most sensitive indicator food through- out the monitoring period. The Se concentration ofmilk is known to be closely dependent on that of feeds (Jacobsen et al. 1965, Conrad and Moxon 1979, Aspila 1991). Thus the present change in the Se concentrations of foods was first observed in milk, in summer 1991 (Fig. 2). About six months later, in December 1991, Se concentrations had started to decrease in all retail foods monitored in the programme (Figs. 1-4). In 1992-1994, the downward trend con- tinued, but more gradually the difference be- tween the annual means being statistically sig- nificant (P<0.01) only for wheat bread and eggs in 1992 and 1993,and for wheat bread and pork fillet in 1993 and 1994 (Table 3). The Se concentrations of spring cereals (spring wheat, barley and oats) have decreased by more than 60% since 1990 (Table 2). The present level is about 0.1 mg kg' 1 dry matter, which was in fact the original target of cereal grain Se fertilization. Of all foodstuffs, the ef- fect of reducing the amount of Se in fertilizers has been greatest in spring cereals. Mixing im- ported and domestic grains in milling increases the Se concentrations of flours. Consequently, the Se concentrations of flour products differ from those of domestic grains (Tables 2 and 3). Farm-to-farm variations in the Se concentra- tion of barley and oats have diminished along Table 2. Selenium concentration of cereals grown in Finland (mgkg 1 dry matter) in 1984 and 1990-1993. Sample 1984 1990 1991 1992 1993 1994 No. Mean ±SD No. Mean ±SD No, Mean ±SD No. Mean ±SD No. Mean ±SD No, Mean ±SD Spring wheat 12 0.01±0.01 24 0.28±0,08 18 0.12±0.06 14 0.12 + 0.02 21 0.11±0.03 6 0.11 ±0.02 Winter wheat o.ol* 22 0.07 ± 0.04 13 0.04 ± 0.05 9 0.04 ±0.02 15 0.04±0.04 5 0.02 ±O.Ol Rye 10 0.01 ±O.Ol 23 0.07 ± 0.03 15 0.06 ±0.03 8 0.03 ±O.Ol 18 0.03±0.02 4 0.03 ±0.02 Barley 50 o.ol** 100 0.23±0.15 100 0.11 ±O.lO 105 0.11 ±0.06 109 0.09±0.05 Oat 49 o.ol** 102 0.24±0.14 101 0.12±0.09 101 o.lo± 0.06 100 0.09±0.07 No. = number of samples * mean for 1972-1976(Koivistoinen 1980). ** Ministry ofAgriculture and Forestry, 1994. Each pooled sample of spring and winter wheat and rye represents 0.1-5 million kg of grain. Barley and oats samples are non-pooled samples from single farms. 379 AGRICULTURAL SCIENCE IN FINLAND Ekholm , P. et al.: Selenium concentration ofFinnish foods Table 3. Selenium concentration of Finnish basic foodstuffs (mgkg 1 dry matter) in 1984, 1990,and 1992-1994. Sample 1984 1990 No. 1992 No. 1993 No. 1994 No. Mean ±SD No. Mean ±SD No. Mean ±SD No. Mean ±SD No. Mean ±SD Wheat flour, medium coarce 33 0.06 ±0.03 20 0.23 ±0.02 Rye flour,whole meal 33 0.09 ± 0.05 24 0.05 ±O.Ol Wheat bread, white 24 0.05 ±0.04 16 0.23 ±0.02 Rye bread, whole 24 0.07 ±0.05 15 0.06 ±0.02 Beefsteak 24 0.17 ±0.06 16 0.64 ±O.OB Pork fillet 24 0.35 ±0.07 16 1.09 ±0.09 Liver, bovine 24 0.65 ±0.29 16 1.47 ±0.38 Liver, porcine 24 1.60 ±0.29 16 2.13 ±0.21 Milk, standard 3.9% fat 24 0.06 ±O.Ol 16 0.21 ±0.05 Cheese, edam 24 0.09 ±0.02 16 0.42 ±0.04 Egg 24 0.69 ±0.15 16 1.26 ±0.13 19 0.14 ± 0.04 20 0.12 10.02 20 0.1110.03 20 0.0710.05 20 0.0610.03 20 0.0410.02 16 0.1610.03 16 0.1310.03 16 0.1010.03 16 0,0610.03 16 0.0710.03 16 0.0510.01 16 0.4910.05 16 0.4610.05 16 0,4210.05 16 0.7710.09 16 0.7110.08 16 0.6410.06 16 1.2110.22 16 1.1510.17 16 1.1010.19 16 1.9010.17 16 1.9510.16 16 1,8610.21 16 0.1510.02 16 0.1410.02 16 0.1310.01 16 0.2910.02 16 0.2710.02 16 0.2510.02 16 0.9910.18 16 0.8510.08 16 0.8910.11 No. = number of samples with the change in fertilizer composition, as was indeed intended by the switch to one-level Se supplementation. The same reduction in varia- tion was evident in the composition of grassy feeds (Ministry of Agriculture and Forestry 1994). Fig. I. Trends in selenium concen- trations of wheat flour (©—©) and rye flour (�—�). Selenium fertilization was started in summer 1985, and the level of supplemen- tation adjusted in summer 1991. Fig. 2. Trends in selenium concen- trations of milk (© —©) and cheese (�—�), 380 AGRICULTURAL SCIENCE IN FINLAND The overall effect of Se supplementation has been noticeable slight on winter cereals (winter wheat and rye), Se concentrations never exceed- ing 0.1 mg kg '. This difference from spring ce- reals is mainly due to the difference in fertiliza- tion practice. However, starting in 1991, the Se concentrations of winter cereals have also de- creased (Table 2). Se concentrations have declined less in other foods than in spring cereals, due to the fact that the lower Se level fertilizers (Se 6 mg kg ') were mainly used in grassy feed production. The Se concentrations of milk, cheese and eggs have decreased by 30-40% since 1990.The Se level of milk is still two to three times higher than that prevailing before Se supplementation practice (Table 3). The use of selenite-supple- mented commercial feeds was already common in egg production in the 1970 s and 1980s. Con- sequently, in 1994 the Se concentration of eggs Voi 4: 377-384. was only slightly higher than that in 1984, be- fore Se was added to fertilizers. The change to one-level Se fertilization has decreased the beef Se concentration by more than 30%, and pork Se by 40% (Table 3, Figs. 3 and 4). The changes have been less marked in bovine and porcine livers than in the corresponding musculous tissues. The Se concentrations of skel- etal muscles and other soft tissues are known to be linearly dependent on the Se concentration of the diet, and to reach a plateau level with the rising Se (Mahan and Moxon 1978, Sankari 1985, Eschewaria et al. 1988). The Se concen- tration of liver reaches its plateau at a lower di- etary level (Se 0.25 mg kg ' fodder) than muscu- lous tissue (over 0.40 mg kg’ 1 fodder) (Ekholm et al. 1991b). The present Se concentration of feeds is still high enough to keep the Se concen- tration of liver near its saturation level. The decrease in the concenration of Se in Fig. 3. Trends inselenium concen- trations of pork fillet (© —©) and beef steak (�—�). Fig, 4. Trends in selenium concen- trations of bovine liver (©—©) and porcine liver (� �). 381 AGRICULTURAL SCIENCE IN FINLAND i Ekholm , P etal: Selenium concentration ofFinnishfoods fertilizers has lowered the average daily human intake of Se. In 1994, the intake was 0.08 mg d 1 as calculated from Finnish food consumption statistics at an energy level of 10 MJ (2400 kcal) (Agricultural Economics Research Institute 1993) (Fig. 5). This is well within the recom- mendations of the United States (0.055 mg for women and 0.070 mg for men) (National Acad- emy of Sciences 1989) and Scandinavia (0.03- 0.06 mg day 1 (Nordic Council of Ministers 1989). Average Se intake is still higher in Fin- land than in most other European countries, and is at almost the same level as in some parts of the United States and Canada (Levander and Morris 1984, Dokkum et al. 1989, Öster and Prellwitz 1989,Bratakos and loannou 1991, Pen- nington and Young 1991). About 40% of the Se intake comes from meat, 24% from dairy products and eggs, and 11% from fish. Animal protein is thus the main source of dietary Se. Cereal products account for 19% of total intake. Overall Se intake may still be de- creasing slightly (Fig. 5). In Finland, imports of Se rich North Ameri- can wheat had a major impact on average daily Se intake in the 1970 s and early 1980 s (Varo and Koivistoinen 1981). During the use of Se-sup- plemented fertilizers grain imports have had only a moderate effect on Se intake. In 1988-1989 of imported wheat consisted relatively high proportion, about 25% of commercial milling. However, the Se intake was slightly lower in 1989 than in 1991, when all milled wheat was again domestic. The Se concentration of mothers’ milk cor- relates well with the estimated Se intake (Fig. 6). During the period of Se supplementation, the Se concentration of breast milk increased from 0.05 mg kg’ 1 dry matter in 1977 (Koivistoinen 1980) to about 0.11 mg kg 1 dry matter in 1990. In comparison with cow’s milk the Se concen- tration of human milk is low due to its lower protein concentration. The effect of decreased dietary Se intake on the Se concentration of breast milk was evident in 1992. No futher de- crease was noted in 1994, indicating that Se in- take is reaching a new plateau. Changes in the serum Se of both the urban and rural population have been consistent with changes in the estimated average Se intake (Min- istry of Agriculture and Forestry 1994). This confirms the validity of the method used in to calculate average intake. The present level of Se in foods guarantees a safe and adequate intake with all kinds of diets. Fig. 5. Average daily selenium intake in Finland at energy level of 10 MJ. Fig. 6. Trend in selenium concentration ofhuman milk. 382 AGRICULTURAL SCIENCE IN FINLAND Vol. 4: 377-384. Excessive food-based intakes are not possible, not even in exceptional dietary compositions. In Finland the Se supplementation offertilizers has proved to be an effective, safe and controlled way of bringing the Se intake of the whole popula- tion up to a nutritionally adequate level. References Agricultural Economics Research Institute 1993. Bal- ance sheet for food commodities. Helsinki. 8 p. Aspila, P. 1991. Metabolism of selenite, selenomethio- nine and feed-incorporated selenium in lactating goats and dairy cows. Journal of Agricultural Science in Fin- land 63: 1-74. Bratakos, M. S. & loannou, P. V. 1991. Selenium in hu- man milk and dietary selenium intake by Greeks. The Science of the Total Environment 105; 101-107. Conrad, H. R. & Moxon, A. L. 1979. Transfer of dietary selenium to milk. Journal of Dairy Science 62; 404-411. Dokkum, W. van, Vos, R. H. de, Muys, T. H. & Wesstra, J. A. 1989. Minerals and trace elements in total diets in the Netherlands. British Journal of Nutrition 61: 7-15. Ekholm, P„ Varo, P., Aspila, P., Koivistoinen, P. & Syr- jälä-Qvist,L. 1991b. Transport of feed selenium to differ- ent tissues of bulls. British Journal of Nutrition 66: 49-55, -, Ylinen, M., Eurola, M., Koivistoinen, P. & Varo P. 1991a. Effects of general soil fertilization with sodium selenate in Finland on the selenium content of milk, cheese and eggs. Milchwissenschaft 46: 547-550. -, Ylinen, M., Koivistoinen, P. & Varo P. 1990. Effects of general soil fertilization with sodium selenate in Fin- land on the selenium content of meat and fish. Journal of Agricultural and Food Chemistry 38: 695-698. Echevarria, M. G., Henry, P. R., Ammerman, C. B. & Rao, P. V. 1988. Effects of time and dietary selenium concentration as sodium selenite on tissue selenium up- take by sheep. Journalof Animal Science 66:2299-2305. Eurola, M., Ekholm, P., Ylinen, M., Koivistoinen, P. & Varo P. 1989. Effects of selenium fertilization on the Se content of selected Finnsh fruits and vegetables. Acta Agriculturae Scandinavica 39: 345-350. -, Ekholm, P., Ylinen, M., Koivistoinen, P. & Varo, P. 1990. Effects of selenium fertilization on the selenium content of cereal grains, flour and bread produced in Fin- land. Cereal Chemistry 67: 334-337. -, Ekholm, P., Ylinen, M., Koivistoinen, P. & Varo, P. 1991. Selenium in Finnish foods after beginning the use of selenate supplemented fertilizers. Journal of the Sci- ence of Food and Agriculture 56: 57-70. Jacobsen, S. 0., Oksanen, H. E. & Hansson, E. 1965. Excretion of selenium in the milk of sheep. Acta Veteri- näriä Scandinavica 6: 299-312. Koivistoinen, P. 1980. Mineral element compositions of Finnish foods. I-XII. Acta Agriculturae Scandinavica Sup- plement 22. 171 p. Kumpulainen, J., Raittila, A.-M., Lehto, J. & Koivis- toinen, P. 1983. Electrothermal atomic absorption spec- trometric determination of selenium in foods and diets. Journal of the Association of Official Analytical Chemists 66; 1129-1135. Levander, O. A. & Morris, V. C. 1984. Dietary selenium levels needed to maintain balance in North American adults consuming self-selected diets. The American Jour- nal Clinical Nutrition 39; 809-815. Mahan, D. C. & Moxon, A. L. 1978. Effects of adding inorganic and organic selenium sources to the diets of young swine. Journal of Animal Science 47; 456-466. Ministry of Agriculture and Forestry 1990. Annual re- port IV. Working Group Report No 12. Helsinki. 29 p. (in Finnish). - 1994 Annual report. Working Group Report No 2. Hel- sinki. 36 p. (in Finnish). National Academy of Science 1989. Recommended Dietary Allowances. 10th ed. National Research Coun- sil, Washington, 284 p. Nordic Council of Ministers 1989. Nordic dietary re- commendations. Report 2. Copenhagen. 16 p. Oster, 0. & Prellwitz, W. 1989. The daily selenium in- take of West German Adults, Biological Trace Element Research 20: 1-14. Pennington, J. A. T. & Young, B. E. 1991. Total diet study nutritional elements, 1982-1989. Journal of the American Dietetic Associaton 91: 179-183. Sankari, S. 1985. Plasma glutathione peroxsidase and tissue selenium response to selenium supplementation in swine. Acta Veterinaria Scandinavica 81: 1-127, Varo, P. & Koivistoinen, P. 1981. Annual variations in the average selenium intake in Finland: Cereal products and milk as sources of selenium in 1979/80. International Journal of Vitamin and Nutrition Research 51: 79-84. -, Alfthan, G., Ekholm, P., Aro, A. & Koivistoinen, P. 1988. Selenium intake and serum selenium in Finland: Effects of soil fertilization with selenium. The American Journal of Clinical Nutrition 48: 324-329. 383 AGRICULTURAL SCIENCE IN FINLAND Ekholm, P. et al: Selenium concentration ofFinnish foods SELOSTUS Seleenilannoituksen muutoksen vaikutus suomalaisten elintarvikkeiden seleenipitoisuuteen Päivi Ekholm, Maija Ylinen, Pekka Koivistoinen ja Pertti Varo Helsingin yliopisto Seleenilannoituskäytäntöämuutettiin siten, että vuo- desta 1991 alkaen kaikissa moniravinnelannoitteissa on ollut yhtä paljon natriumselenaattia (Se 6 mg kg' 1 lannoitetta) aikaisemmin käytetyn kahden seleenili- säyksen sijasta. Toimenpiteellä haluttiin ennen kaik- kea estää eläinten rehuissa esiintyneitä suuria selee- nipitoisuuksia, joita oli havaittu eräissä yksittäista- pauksissa. Kaikkien seurattujen elintarvikkeiden seleenipi- toisuudet olivat laskeneet lannoituskäytännön muu- toksen vuoksi. Kevätviljojen seleenipitoisuudet oli- vat laskeneet eniten (yli 60 %), koska vuosina 1985- 1990 lannoitteissa käytetty seleenitaso 16 mg kg 1 oli tarkoitettu viljanviljelyyn. Muiden elintarvikkeiden seleenipitoisuudet olivat laskeneet vähemmän kuin kevätviljojen. Lihan seleenipitoisuus oli laskenut n. 30 %, maidon ja juuston yli 30 %. Muutos on ollut pienin naudan ja sian maksan kohdalla (10-20 %). Elintarvikkeiden seleenipitoisuuksien lasku oli vaikuttanut myös suomalaisten keskimääräiseen päi- vittäiseen seleenin saantiin Suomessa. Vuonna 1994 seleenin saanti oli 10 MJ:n energiatasolla 0,08 mg d'. Seleenin saantimme vastasi hyvin kansainvälisiä suo- situksia ja oli riittävä ja turvallinen. 384 AGRICULTURAL SCIENCE IN FINLAND