STUDY ON A CONTENT OF MERCURY IN HAIR, MILK AND BLOOD OF COWS HOUSED IN AN URBANIZED AREA

Zbigniew Dobrzański¹, Tadeusz Szulc², Robert Kupczyński³, Marian Kuczaj^4
1 Department of Environment Hygiene and Animal Welfare, The Faculty of Biology and Animal Science, Wrocław University of Environmental and Life Sciences, Poland
² Institute of Animal Breeding, Wrocław University of Environmental and Life Sciences, Poland
³ Department of Environmental Hygiene and Animal Welfare, Wrocław University of Environmental and Life Sciences, Poland
⁴ Institute of Animal Breeding, Faculty of Biology and Animal Science, Wrocław University of Environmental and Life Science, Poland

ABSTRACT

Research on a content of mercury in 24 dairy cows (an average daily milk yield – 22.23 kg) of PHF breed (black-white and red-white colour, divided into primiparous and multiparous ones) housed in a farm system in suburban area were conducted. Concentration of a metal was determined using TMA-254 spectrophotometer in unwashed samples of hair (overall content) and in washed ones (assimilated content) as well, and also in full blood and raw milk.  The biggest amount of mercury was observed in hair (max 6.5 µg·kg^-1 d.m.), then in blood (max 2.0 µg·l^-1), ad the lowest amount was in milk  (max 0.6 µg·l^-1). Difference between Hg content in raw and washed hair was 26.5%. Content of Hg in milk did not exceed a limit established by a Decree of Ministry of Health (10 µg·kg^-1) in any sample. Statistically significantly higher content of Hg was in hair of cows of black-white colour comparing to red-white (p<0.01). Any influence of cows' performance period (primiparous, multiparous) on Hg content in hair, milk and blood was observed. Any significant correlations between Hg content in hair and a concentration of that element in blood and milk were noted.

Key words: mercury, cow, hair, milk, blood.

INTRODUCTION

Mercury inhibits a strong chemical and biological activity and a changeability of a form (liquid and gaseous). It is not used in life processes of plants, animals and human however it belongs to strong environmental poisons, especially in organic forms [21,31]. Toxic activity of mercury causes disorders in enzymatic system functioning, and changes in an area of phosphoric bonds of DNA, that is connected with its further mutagenic, embryotoxic and teratogenic  activity  [16,26].

According to Virtanen et al. [36] and Zair et al. [39] mercury is an important factor causing a number of metabolic changes and disorders, including neurological, nephrological, immunological, cardiological, motoric, reproductive and even genetical in human.  In animal organisms mercury shows an antagonism with Cd, Zn and I, and disturbs metabolism of  Cu. Its availability is limited by selenium [15,24].

An important source of mercury emission into an environment is mining and steel industry, oil processing, industrial processes using mercury and its compounds, cement and electrotechnical devices production, combustion of coal and oil products, industrial sewage,  waste lagoons etc. [4,13,27,38]. Small amount of mercury is included in chemical fertilizers and feed additives (phosphates), liquid manure and composts [19,30]. Mercury easily moves from an environment to plant and animal organisms, that may locally lead to an increased accumulation of that toxic metal in products of animal origin like meat, milk, eggs, fats, fish tissues, bee products [2,7,22,42,40]. It should be added that not only a concentration of Hg in food products, but also so called PTWI index (Provisional Tolerable Weekly Intake), i.e. weekly intake of a given element with food, are of an importance. According to data of  FAO/WHO – JECFA for long years that index for mercury was 0.3 mg, including 0.2 mg in a form of methyl mercury, and since 2003 the latter value has been limited to 1.6 µg·kg^-1 of body mass. That means an acceptable intake for an adult man on a level of only 0.112 mg Hg·week^-1 [25,34].

Milk and blood are good indicators, however there are mechanisms limiting a bioaccumulation of Hg in tissues and organs of animals [18,28]. Products of skin and  epidermis, i.e. hair, coat, bristle, wool or feathers are better and non-invasive indicators, they enable an assessment of mercury bioavailability from an environment (overall content) and from feed and water (available content) [6,9,11,17,32,].

The aim of the work is an assessment of mercury content in hair, blood and milk of cows housed in farm system in an urbanized area (suburban).

MATERIAL AND METHODS

Research material was collected in early autumn period from cows of Polish Holstein-Friesian breed (PHF) of black-white (bw) and red-white (rw) colour. The farm is situated on an area of Wroclaw city (Psie Pole district), and cows are kept in free-stall system, feeding was based on TMR (total mixed ration) system. Animals were not grazed but made use of yards. An average annual milk yield of cows on a farm was about 8500 kg.

Samples for the study were collected from 24 cows (clinically healthy) that were in lactation period (up to 100th day), 12 primiparous and 12 multiparous ones (2–4 lactation). Half of each age group consisted of animals of black-white colour (bw), and next part animals of red-white colour (rw).

Representative samples of milk were collected during afternoon milking to special plastic containers. Blood was collected after milking from neck external cervical vein to test-tubes with EDTA (full blood). Hair was obtained by cutting with an electric razor from 2 sites: withers area and area of chest, in equal amounts that then were mixed. The material (mass about 5–6 g) was subjected to cleaning process, where foreign substances were removed. Then hair was divided onto two parts. First of them were raw samples (unwashed) for determination of an overall mercury content. Remaining material, in order to determine an assimilated content, was subjected to cleaning (washing) in warm water with a detergent, and then it was rinsed twice in distilled water and subjected to natural drying. Such prepared samples were homogenized using a special mill, and in sterile foil sacks transferred to analytical laboratory.

Also feed (TMR), drinking water from automatic drinking bowls and soil from a yard were once collected for analyses. Feed and soil were dried and grinded.

A determination of an overall and assimilated Hg content was done using method of an atomic absorption spectrophotometry (AAS), technique of flameless amalgamation with the use of TMA-254type analyzer of Tesla company (smallest detectable amount of Hg – 0.2 ng). Certified DOLT-2 and DORM-2 preparations (Canadian Certified Reference Material Project Company) were a reference material.

Analysis of chemical content (fat, protein, lactose, dry matter, non-fat dry matter) in representative milk samples collected at the same time that other material was done using  Milko-Scan 133 B apparatus (Foss Electronic Company).

Results were subjected to statistical analysis, mean values () and standard deviations (s) were calculated, and a significance of differences between groups (with division on primiparous and multiparous cows, and black-white and red-white colour) was assessed with t-Student's test. Also correlation coefficients (r) between Hg content in hair, milk and blood were calculated. All statistical calculations were done using Statgraphics 5.1. software.

RESULTS AND DISCUSSION

Milk yield on a day of a study was on average on a level of 22.23 kg from a cow (Table 1). Any significant differences in a content of particular components (fat, protein, lactose, dry matter) were observed between primiparous and multiparous cows, similarly like in the case of cows' genotypes (bw and rw). Thus, milk composition with respect to a content of main components was similar in all groups.

Table 1. Milk yield and its chemical composition – cows of PHF breed

Cow (n=12)		Milk (kg)	Fat (%)	Protein (%)	Lactose (%)	Dry matter  (%)	Non-fat dry matter (%)
Primiparous		20.38	4.66	3.25	4.57	13.09	8.43
	s	4.51	1.12	0.22	0.10	1.27	0.22
Multiparous		24.08	4.16	3.16	4.53	12.44	8.28
	s	3.79	1.03	0.13	0.26	1.05	0.32
Black-white colour		23.56	4.43	3.21	4.56	12.79	8.37
	s	3.27	1.13	0.16	0.25	1.21	0.33
Red-white colour		20.90	4.40	3.20	4.54	12.74	8.34
	s	5.11	1.08	0.21	0.12	1.21	0.23
Mean (n=24)		22.23	4.41	3.20	4.55	12.76	8.35

Content of mercury in hair of cows is presented in Table 2. Statistically higher (p<0.01) content of overall mercury (in unwashed samples), on a level of 3.39 µg·kg^-1 d.m, was observed comparing to content of assimilated mercury that was 2.49 µg·kg^-1 d.m. Thus, 26.5% of mercury included in hair was probably coming from an environment, air pollution (dust) and a base (droppings, soil). Any significant differences between primiparous and multiparous cows were noted, in the case of an overall and assimilated Hg as well. Thus, the length of cows performance do not influence a content of Hg in hair in a significant manner, that may be connected with a constant replacement of hair in animals. Maximal content of Hg was 6.5 µg·kg^-1 d.m.

Table 2. The content of Hg in hair of cows of PHF bred (µg·kg-1 d.m.)

Cow (n=12)	Overall content	Assimilated content
Primiparous	3.27A ± 0.71	2.42B ± 0.43
Multiparous	3.52A ± 1.22	2.57B ±0.39
Black-white colour	4.00A ± 1.04	2.77B ± 0.31
Red-white colour	2.78A ± 0.40	2.22B ± 0.32
Mean (n=24)	3.39A ± 0.98	2.49B ± 0.41

A – B – p ≤ 0.01 (between overall and assimilated content)

It may be concluded from the research by Dobrzański et al. [11] that an average overall content of Hg in hair of cows from farm keeping system was 0.015 mg·kg^-1, while assimilated content was of 33.3% lower from an overall content. On areas of gold mine influence in Brazil an average concentration of Hg on a level of 0.1 mg·kg^-1 was observed in cows' hair [27], and on an area of mercury mine in Germany the content of Hg in sheep wool was 0.107 mg·kg^-1 on average [16]. According to Bodkowski et al. [6], an average content of Hg in sheep wool on an area of copper industry was 0.19 ppm, while on areas ecologically clean it was 0.12 ppm (120 µg·kg^-1). That testifies the influence of industry on accumulation of that element in animals. In a context of that information it should be recognised that obtained in a present study concentrations of Hg were low, that proves the small influence of urbanization on Hg accumulation. Content of Hg was also low in given feed (0.01 mg·kg^-1 d.m.) and in drinking water on a farm (0.04 mg·l^-1). In turn, in upper layer of soil from yards the noted content of Hg was 0.066 mg·kg^-1 d.m. that should also be considered as a low value in a context of other data [4,41].

Comparing both breeds, the statistically higher (p<0.01) content of overall and assimilated mercury was observed in hair of cows of black-white (bw) colour, comparing to red-white (rw) ones. This is probably connected with a content of pigments in hair. From research of Krośnicka-Bombała [23] it may be concluded that content of pigments in coat of sheep and goats influences an accumulation of some elements. The author observed positive correlations between the content of eumelanin and concentration of  Fe, Cu, Mn, K, Na and Mg (Hg was not analysed).

An average concentration of Hg in full blood was a few fold lower than in hair (Table 3). In the case of primiparous cows it was 0.84 µg·l^-1 on average, while in multiparous ones it was 1.05 µg·l^-1. Maximum value was 2.0 µg·l^-1. Any significant differences between these groups, or between genotypes of cows (bw and rw) were noted. Obtained concentrations are considered to be rather low. In cattle in mining area of Brazil, an average value observed in blood was 11.7, and in pigs it was 15.7 µg Hg·l^-1 [27], while in older calves in agricultural Galicia, the maximum value of Hg in blood was 13.4 µg·l^-1, and in industrialized Asturias (Spain) it was only 2.76 µg·l^-1 [1]. Concentration of Hg in blood of human is usually in a range of <0.25–9.9 µg·l^-1 [10,18], however in industrialized areas it may be considerably higher [41].

Table 3. The content of Hg in blood and milk of cows of  PHF breed (mg·l-1)

Cow (n=12)	Blood	Milk
Primiparous	0.84 ± 0.19	0.24 ± 0.06
Multiparous	1.05 ±0.30	0.27 ±0.07
Black-white colour	1.02 ±0.26	0.28 ±0.09
Red-white colour	0.87 ± 0.25	0.23 ± 0.08
Mean (n=24)	0.945 ± 0.24	0.255 ± 0.07

Results of a study on Hg content in raw milk are presented in Table 3. An average concentration was 0.24 in primiparous cows and 0.27 ppb (µg·l^-1) in multiparous ones. Maximum content was 0.6 µg·l^-1. Differences between cows wb and rb were not significant statistically.

There is a great deal of data concerning an accumulation of mercury in milk of cows kept on industrialized as well as typically agricultural regions in literature available. Dobrzański et al. [12] observed that content of Hg in milk of cows from different regions of Silesian macro-region was in a range of  0.3–6.7 µg·l^-1. In the late 80 years, Żmudzki et al. [42] noted an average content of Hg on a level of 2 µg·kg^-1 on average (max. 8 µg·kg^-1) in milk of cows in Zgorzelec-Bogatynia region. A permissible limit of Hg concentration in milk as food product was officially established as 10 µg·kg^-1.

In milk in Spain (Canary Island) an average value of Hg was established on a level of  0.09–0.61 µg·kg^-1 [29], while in China it was 1.0–3.9 µg·kg^-1 [41]. In Italy in an area of Rome that content was considerably higher, i.e. 0.9–38 µg·kg^-1 [37], while in southern part of that country only 2–3 µg Hg·kg^-1 d.m. [7]. High concentrations were observed in milk products in Egypt, they reached even 86–556 µg·kg^-1 [3]. In that context, the information that woman's milk may contain from 0.2 to 20.3 µg Hg·l^-1 seems to be interesting [14,33].

It is generally believed that Hg transport to blood or milk from respiratory or alimentary system depends on a form of Hg, since only alkyl combinations (e.g. methyl mercury) are transferred easily, while inorganic ones are removed with droppings (urine, faeces). Grega and Barowicz [18] reveal that Hg like other metals (Al, Pb, Zn, S) are first deposited in various organs (liver, kidneys, brain), and then may penetrate from blood to milk, while a mammary gland itself is a kind of biological barrier [10,28]. It is known that Hg may create plenty of durable complexes with proteins and other compounds, mainly that including SH groups [20]. According to Sundberg et al. [33] casein, fat and whey fraction of mice milk accumulate mercury from methyl mercury in percentage amounts of 11:39:34, while from inorganic form in a ratio of 31:15:41 (%), respectively, in relation to an overall Hg content in milk of these animals. 

Content of Hg in feed, drinking water and to a smaller extent in the air, may have some influence on an occurrence of elevated Hg concentrations in milk. Chodorowski et al. [8] observed a high, i.e. 23 µg·kg^-1, concentration of Hg in milk after feed contamination with metallic mercury. In turn Dobrzański and Tarnacka [13] proved that Hg content in milk of cows in the vicinity of electrotechnical industry waste lagoon was 3 µg·l^-1, despite that in forage grass maximum values reached up to 1730 µg·kg^-1 d.m. what confirms that inorganic forms of that element are available to a very small extent. 

Any statistically significant correlations between Hg content in hair and concentration of that element in blood and milk were noted. Value of correlation coefficient (r) oscillated in a range of -0.102 to 0.117. Probably with bigger amount of samples the value of that coefficient would have been different, especially in the case of relationship between blood and milk or hair and blood. A positive correlations  (r=0.87÷0.93, p<0.001) between Hg concentration in feathers and blood in sea birds Larus canas L (common gull) were demonstrated by Kahle and Becker [20], while Björnberg et al. [5] give significant correlations (r=0.32÷0.037, p<0.001) between Hg concentration in hair of women in Sweden and a content of that element in blood. High correlation between Hg concentration in blood and milk of cows in urbanized regions was reported by Hindu authors [35].

Summing up, it should be stated that farm keeping of dairy cows in urbanized (and industrialized) region  do not possess any ecotoxicolgical threat for that animals, and observed Hg concentrations in raw milk ought to be considered as low.

CONCLUSIONS

1. A low concentration of mercury was noted in raw milk of cows kept in urbanized region with respect to information from national and international literature and a standard officially accepted for that element on a level of 10 µg·kg^-1. 

2. Any statistically significant relationship between Hg content in hair and a concentration of that element in milk and full blood of cows were observed.

3. It was observed that the length of performance period of cows (primiparous, multiparous) does not influence Hg content in hair, milk and blood.

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Accepted for print: 4.03.2009

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Zbigniew Dobrzański
Department of Environment Hygiene and Animal Welfare, The Faculty of Biology and Animal Science, Wrocław University of Environmental and Life Sciences, Poland
J. Chełmońskiego 38 C
51-630 Wrocław
Poland
Phone: +48 71 320 5865
email: zbigniew.dobrzanski@up.wroc.pl

Tadeusz Szulc
Institute of Animal Breeding,
Wrocław University of Environmental and Life Sciences, Poland
Chełmońskiego 38C, 51-630 Wrocław, Poland
phone: 71 320 57 62
email: tadeusz.szulc@up.wroc.pl

Robert Kupczyński
Department of Environmental Hygiene and Animal Welfare,
Wrocław University of Environmental and Life Sciences, Poland
Chełmońskiego 38 C, 51-630 Wrocław, Poland
Phone: (+48 71) 320 59 41
email: robert.kupczynski@up.wroc.pl

Marian Kuczaj
Institute of Animal Breeding, Faculty of Biology and Animal Science, Wrocław University of Environmental and Life Science, Poland
Chełmońskiego 38 C
51-630 Wrocław, Poland
Phone +48 71 32-05-860
fax: +48 71 32-05-764
email: marian.kuczaj@up.wroc.pl

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