Cadmium, lead and mercury levels in feeding yeast produced in Czechoslovakia

The Science of the Total Environment, 114 (1992) 73-86 Elsevier Science Publishers B.V., Amsterdam

73

Cadmium, lead and mercury levels in feeding yeast produced in Czechoslovakia Jii~i Cibulka a, Tomfig Turecki a, Daniela Miholovfi a, Pavel Mader a, Jifina Szfikovfi b and Marek Brabec a ~University of Agriculture, Department of Animal Physiology and Zoology, CS-16521 Prague 6, Czechoslovakia bAgricultural Enterprise, Louny, Czechoslovakia (Received May 8th, 1990; accepted December 31st, 1990)

ABSTRACT Ninety-six samples of the feeding yeast known as VITEX were analyzed for Cd, Pb and Hg content during 1987-1989. Cadmium content ranged from 0.30 to 5.12 mg- kg -~, lead content from 0.21 to 3.01 mg • kg -l and mercury content from 0.008 to 0.187 rag' kg -l. Our findings meet the current government standards (max. allowed Pb = 5.00, Cd = 0.50 and Hg = 0.100 mg" kg -I) only for lead, and with five exceptions, for mercury, With two exceptions, all cadmium levels found in the samples exceeded the limit. One raw material - - the wood chips - - was shown to be the main source of cadmium in the technological process. Relatively high Hg contents were measured in the wood chips (up to 0.155 mg" kg-l); the highest Hg level (1.105 m g ' kg -l) however was found in a sample of KOH.

Key words: cadmium; lead; mercury; feeding yeast; monitoring

INTRODUCTION

The fact that yeast cells accumulate hazardous elements has been known for several years (Rossi, 1976; Burgerovfi, 1981; Wolf et al., 1982; t~ernfi, 1988). In Czechoslovakia, a unique biotechnology was developed by BIOCEL, Paskov. There, spent sulphite liquor from a wood-pulp mill is used as a medium for Candida utilis cultivation. The dried yeast material is sold under the commercial name VITEX. Klement (1987) found 0.64 mg Cd. kg -l in VITEX yeast and Drfipal (1989) stated that elevated cadmium levels in VITEX yeast have been observed for several years. According to data provided to us by Sedlbauer (pers. commun.), the cadmium content in VITEX yeast ranged from 0.04 to 4.30 mg Cd. kg -~, the lead content from 0.30 to 0.90 mg P b - k g -~, and the mercury content from 0.010 to 0.027 mg Hg. kg -1 during the period of January to September, 1989. If a large-scale 0048-9697/92/$05.00

© 1992 Elsevier Science Publishers B.V. All rights reserved

74

J. CIBULKA ET AL

use of VITEX yeast in animal nutrition is adopted, the possible contamination of the feeding yeast by cadmium, lead and mercury represents a serious danger. MATERIALS AND METHODS

Yeast sampling A total of 96 yeast samples were collected between 1987 and 1989 in a yeast producing plant (BIOCEL, Paskov, Czechoslovakia). The samples (weighing - 5 0 0 g each) were wrapped in paper bags and transported to the Trace Laboratory of the Department of Animal Physiology and Zoology, University of Agriculture, Prague. The samples were stored in a dust-free environment at room temperature until analysis. For purposes of comparison, a set of six samples of baker's yeast bought randomly in several shops in Prague and in Mnigek pod Brdy, Czechoslovakia was analyzed in addition to samples of the feeding yeast MOZYR from the USSR, an ethanol yeast from Kojetin (Czechoslovakia) and the yeast ATTISHOLZ produced in Switzerland.

Process inputs and interproducts sampling Samples of intermediate products from different stages of the process were taken four times during the period monitored: sulphite liquor after sulphur dioxide stripping, enriched sulphite liquor, washed yeast milk from separation and brewed spent sulphite liquor from the first separation. A sample of feeding yeast was collected at the same time. Samples of the main process constituents were taken at the same time: phosphoric acid, potassium hydroxide, water, wood chips, defoamer, molasses + sulphite liquor (1:1), non-bleached and final cellulose. Liquid samples were placed in plastic bottles (1 1), which had been soaked for several days in diluted nitric acid to prevent secondary contamination. Solid samples (wood chips, cellulose) were packed in plastic bags.

Analytical procedures Sample preparation The liquid samples were prepared for analysis immediately after transportation to the laboratory. The solid samples were stored at room temperature until analysis. The dry ashing procedure was the same for all samples; only sample weights were different. The sample weight for feeding yeast was - 1.5 g and

CADMIUM, LEAD AND MERCURY LEVELS IN FEEDING YEAST

75

2-15 g for other solid samples. The volume of the water samples used was 50 ml. The following dry ashing procedure was used. A sample was weighed in a 50-ml quartz beaker with 1 mg accuracy and dried in a vacuum drier (SPT 200, made in Poland) at 105°C for 24 h. After drying, the samples were charred on a hot plate in a fume hood with the beakers covered by watch glasses. The following temperature timetable was adhered to. First hour at 160°C, second hour at 210°C, third hour at 280°C, fourth hour at 360°C. After charring, the samples were placed in a muffle furnace (LM 122.20 made in GDR) where ashing was carried out as follows: fifth hour at 350°C, sixth hour at 450°C and seventh to twenty-third hours at 500°C. To achieve complete organic material decomposition, an ashing aid in the form of 1 ml of 65% nitric acid (Analar grade) was used. After nitric acid evaporation to dryness, the samples were ashed for a further hour at 500°C in the muffle furnace. The ash was dissolved in 1.5% nitric acid using an ultrasonic bath. The solution was then transferred into calibrated test tubes and 1.5% nitric acid was added to each test tube to bring the volume up to 10 ml. Test tubes were sealed with parafilm and stored until analysis. To every eight real samples, two blanks were added to make a batch. The samples were analyzed in triplicate.

Measurement of prepared samples A flame atomic absorption spectrometer (Varian SpectrAA 40 P) was employed to measure lead and cadmium levels in the samples. Mercury levels were measured using a Trace Mercury Analyser TMA-254 (made in Czechoslovakia). The procedure is based on cold vapor atomic absorption spectrometry. A sample (250 mg) is burned in a catalytic oven in a stream of oxygen at 800-900°C and all mercury released is trapped in an amalgamator from which it is expelled into a flow-through cell. Calibration is performed using standard solutions with concentrations of 0.5 and 5.0/~g Hg. m1-1. The results were expressed in mg of an element per 1 kg of the samples (fresh matter). The average dry matter present in the yeast samples was 92%. The analytical results of interproducts and raw material (apart from water, potassium hydroxide and phosphoric acid) were expressed in mg per 1 kg of sample dry matter.

Analytical accuracy and reliability check The accuracy and reliability of the analytical system used was checked using certified reference material (bovine liver, NBS 1577a) and our own laboratory reference material NSC-2 (bovine liver) and HjP (bovine liver). The results of the control analyses are summarized in Table 1. The detection limits for individual elements measured during the first

76

J. CIBULKA ET AL

TABLE 1 The results of the control analyses of certified reference materials (mg" kg- J) Material NBS 1577a NSC-2 HjP

Pb Cd Pb Cd Hg

Certified

Measured

0.14 0.44 0.45 0.42 0.36

< 0.10 0.44 0.59 0.44 0.36

± ± ± + ±

0.02 0.06 0.09 0.03 0.02

± + ± ±

0.02 0.14 0.02 0.01

series of samples (16/4/87-28/11/88) using 2 g of sample weight were as follows: Pb = 0.40 m g - k g -1, Cd = 0.05 m g - k g -1, Hg = 0.001 m g . k g -1. For the samples analyzed from 29/11/88 to 13/3/89, the detection limits were: Pb = 0.20 m g . k g -l, Cd = 0.12 m g . k g -1 and Hg = 0.001 m g . k g -1. For the third analytical period from 13/3/89 to 17/11/89, the detection limits, using a 1.5 g sample weight, were: Pb = 0.52 m g - k g -1, Cd = 0.03 mg. kg -1 and Hg = 0.001 mg. kg-t.

Statistical procedures The results were worked up to obtain basic statistical parameters (Table 2) using an IBM compatible PC AT computer. Similarities between the empirical frequency distribution of the element concentrations and the models were tested employing the x2-test. RESULTS AND DISCUSSION

From the analyses of 96 samples of the feeding yeast VITEX, it was found that cadmium levels in the samples ranged from 0.30 to 5.12 mg. kg-1, lead levels from 0.21 to 3.01 m g . k g -~ and mercury levels from 0.01 to 0.19 mg- kg- 1 (Table 2). Figures 4 - 6 show the levels of elements in feeding yeast during the monitored years 1987-1989. It can be stated that, comparing these values with the recommended guidelines in feedstuffs, i.e. for Cd = 0.50, Pb = 5.00, Hg = 0.100 m g - k g -1 (Anonymous, 1987), only the lead contents and, with the exception of five samples, the mercury contents, were below the recommended limits. Nearly all samples exceeded the limit for cadmium; the exceptions were two samples. Frequency distribution is distinctly different for the elements studied. Cadmium distribution was bimodal (Fig. 1), and, using the x2-test, this distribution is significantly different from normal and log normal distribution. The

aDimensionless number.

n Arithmetic mean Geometric mean Median Modus S.D. Maximum Minimum Range Standardized skewnessa Standardized kurtosis a

Statistical parameter

23 1.48 I. 14 0.82 0.80 1.28 4.57 0.55 4.01 3.41 1.91

43 3.68 3,43 3.96 3.93 1.04 5.12 0.93 4.19 -3.70 1.73 30 2.93 2.32 3.52 3.17 1.49 5.12 0.30 4.82 -1.21 -1.27

96 2.91 2.33 3.65 4.36 1.51 5.12 0.30 4.82 -1.68 -2.81

87-89 23 0.50 0.46 0.43 0.30 0.22 1.12 0.30 0.82 2.69 1.73

87

89

87

88

Pb

Cd

Basic statistical parameters of Cd, Pb and Hg levels (mg • k g - 1) in VITEX yeast

TABLE 2

43 0.59 0.55 0.55 0.50 0.20 1.04 0.21 0.84 0.86 -0.38

88 30 0.75 0.64 0.59 0.54 0.53 3.01 0.29 2.72 6.51 12.04

89 96 0.62 0.55 0.52 0.50 0.35 3.01 0.21 2.80 14.74 43.28

87-89 23 0.067 0.061 0.064 0.076 0.032 0.171 0.031 0.140 3.306 4.232

87

Hg

43 0.025 0.021 0.021 0.011 0.016 0.094 0.008 0.086 5.739 8.924

88

30 0.053 0.044 0.043 0.029 0.037 0.187 0.018 0.169 4.692 5.797

89

96 0.044 0.034 0.034 0.019 0.033 0.187 0.008 0.179 7.625 9.716

87-89

"-.d

o~

.<

-¢

~r

Z

,7,

~r

78

J. CIBULKA ET AL

18

15

12

~9

L L&.

0

1

2

3 4 Cd [rag' kg -13

5

6

Fig. 1. Frequency histogram of cadmium levels (mg" kg -l) in VITEX yeast in 1987-1989.

distributions of lead and mercury values (Figs. 2 and 3) are not significantly different from the log normal model. Considering these facts, we will use only the range for Cd in the text below. For lead and mercury, geometric mean (~g) will be used, which is more suitable than routinely used arithmetic mean (xPb = 0.62 mg. kg -1 and X'gPb = 0.55 mg.kg-~; xng = 0.044 m g - k g -1 and Xgng = 0.034 mg. kg-l). Figure 4 describes a distinct elevation of cadmium content in 1988 (3.00-5.00 mg Cd • kg -~) compared to 1987 (0.50-1.00 mg Cd • kg-~). This fact could be explained by the appearance of a more contaminated wood from a new locality in the process during 1988. We are not able to prove this hypothesis. For the year 1989, a slight decrease in cadmium content may be observed. Figure 4 shows that more samples had cadmium levels below 1.00 mg C d . k g -I (1988 - - one sample, 1989 - - six samples). However, 11 samples had extremely high cadmium contents ( > 4.00 mg Cd. kg-1). There is a slight elevation in the lead levels o f the samples of VITEX yeast during the monitored years (xg87 = 0.46 m g . k g -l, Xg88 = 0.55 m g - k g l and xgs9 = 0.64 mg.kg-1). The average lead content (~-g) of the samples during the 3 years was 0.55 mg P b . k g - I (Fig. 5).

79

CADMIUM, LEAD AND MERCURY LEVELS IN FEEDING YEAST

40-

~, 3o-

\ lo.

\

/

\\ \

0

1

2 Pb [ m g . k g "1]

3

4

Fig. 2. Frequency histogram of lead levels (mg" kg -1) in VITEX yeast in 1987-1989.

20-

16

~- 12u_ .

8

t//

\ \

\

:

\

\\ \ 0

~

0,01

f

0,03

Q07

0,11 Hg [mg,kg "1]

I

0,15

'

'

'

I

0,19

'

"

"

i

0,23

Fig. 3. Frequency histogram of mercury levels (rag-kg-I) in VITEX yeast in 1987-1989.

80

J. CIBULKA ET AL.

6-

5-

% ~3

.E.

8/4/87

12/1/~

2/1/89 Date of sampting

17/11/89

Fig. 4. Cadmium levels in samples of VITEX yeast in 1987-1989 (Czechoslovak limit 0.5 mg- kg - i).

The average mercury content (%g) in VITEX yeast during 1987-1989 was 0.034 mg Hg. kg -~. An observed decrease in values for the individual years 1987 and 1988 were (Xg87 = 0.061 mg.kg-1; xg88 = 0.021 m g . k g -l) did not continue in 1989 (x~89 = 0.044 mg. kg -l) (Fig. 6). Table 3 compares the elemental levels in VITEX yeast with the values for the feeding yeast MOZYR, produced in the USSR; the yeast ATTISHOLZ, made in Switzerland; and a Czechoslovak yeast cultivated on ethanol in Kojetin. It is clear that the cadmium levels in these yeasts are substantially lower than those of VITEX yeast (Kojetin = 0.14 mg Cd. kg-1; MOZYR = 0.06 mg Cd-kg-1). Nevertheless, in A T T I S H O L Z yeast, the Cd level (0.61 mg Cd. kg-1) exceeded the Czechoslovak limit (0.50 mg Cd-kg-1). Since wood chips were determined to be the main source of cadmium, we think that less contaminated raw material explains the lower Cd levels in MOZYR and ATTISHOLZ yeast. In Kojetin, the yeast are cultivated on ethanol. Values for the Cd content of VITEX yeast similar tO those we have found were reported by Klement (1987), who found 0.64 mg C d . k g -l. Sedlbauer (pers. cam-

81

CADMIUM, LEAD AND MERCURY LEVELS IN FEEDING YEAST

3-

orb

~2-

#

0

8/4/87

i

-q . . . . . . . I . . . . . . 12/1/88 2/1/89 Date of sampling

1 17/11/89

Fig. 5. Lead levels in samples of VITEX yeast in 1987-1989 (Czechoslovak limit 5.0 mg" kg-l).

mun.) found from 0.40 to 4.30 mg Cd. kg -~ in VITEX yeast during the period of January to September, 1989 which is also in a good agreement with our results. The lead levels in ATTISHOLZ yeast are substantially higher (1.50 mg Pb. kg -~) than those of VITEX yeast (~g = 0.55 mg Pb. kg-1). Ahlers and R6sick (1985) and R6sick et al. (1986) measured an elevated penetration of Cd into yeast cells when glucose was present in the cultivation medium. In light of this observation, it is important to remember that VITEX yeast biomass cultivation is based on the fermentation of the simple saccharides, including glucose, contained in spent sulphite liquor. Wolf et al. (1982) found 8.10-11.30 mg Pb. kg -~ in a microbial biomass. In Torula, they measured 4.50 mg Pb. kg -l. Our findings in VITEX yeast were 0.21-3.01 mg Pb. kg -1. Summarized results concerning the baker's yeast are in Table 4. There are no valid guidelines in Czechoslovakia for elements in baker's yeast with the exception of lead, which is limited to 5.00 mg. kg- 1. For the evaluation of measured levels of Cd and Hg we could use the limits for 'other food items'

82

J. CIBULKA ET AL

0,20]

0,161

0,12)

f- 0,08.

0,04-

0

. . . . . . I . . . . . . . 12/1/8B 8/4/87

I

'

2/1/89 Date of sampling

'

,

'

'

I

17/11/89

Fig. 6. Mercury levels in samples of VITEX yeast in 1987-1989 (Czechoslovak limit 0.1 mg" kg - i).

(Cd = 0.05; Hg = 0.020 mg. kg-l). However, these limits seem to be very low since Cd levels in six yeast samples analyzed exceeded the limit by 4-fold. All measured Hg values in the baker's yeast were under the current limit for 'other food items' (0.020 mg Hg. kg-1). The same was true of the lead content.

TABLE 3 Cadmium, lead and mercury levels in MOZYR yeast (USSR), ATTISHOLZ (Switzerland), and a y e a s t f r o m Kojetin (Czechoslovakia) (mg" kg-i) Yeast

n

Cd

Pb

Hg

MOZYR ATTISHOLZ Kojetin

1 1 1

0.06 0.61 0.14

0.04 1.50 0.27

0.046 0.013 0.087

yeast

0.01

0.004

0.003

0.003

0.01

0.03

0.23

0.19

0.13

0.20

0.05

0.19

s

0.14

0.19

0.18

< 0.16

0.19

< 0.13

~

s

0.04

0.01

0.04

0.02

0.006

0.006

0.008

0.013

0.011

0.006

~

s

0.003

0.003

0.003

0.005

0.005

0.003

0.06

0.01

0.08

0.05

0.07

0.07

~

0.01

0.002

0.001

0.002

0.003

0.002

s

0.05

0.07

0.06

< 0.05

0.06

< 0.05

~

Pb

Cd

Hg

Cd

Pb

mg • k g - I. of flesh matter

m g • k g - l of dry matter

0.01

0.01

0.01

0.01

s

0.002

0.002

0.003

0.005

0.004

0.002

~

Hg

0.001

0.001

0.001

0.002

0.002

0,001

s

Current Czechoslovak limit ( A n o n y m o u s , 1986; m g " kg -I of fresh matter): Cd = 0.05 (other foodstuffs), Pb = 5.00 (baker's yeast), H g = 0.02 (other foodstuffs).

Praha 10 17/3/88 Praha 4 17/3/88 Praha 4 17/3/88 Praha 1 17/3/88 Mnigek p. Brdy 18/3/88 Praha 3 23/3/88

Place and date of sampling

Cadmium, lead and mercury levels in baker's yeast

TABLE 4

oo ~o

..< r~

t~

~r

Z ~7

r." rn

84

J. CIBULKA ET AL

TABLE 5 Cadmium, lead and mercury levels in samples of interproducts and process inputs (mg- kg- 1 of dry matter) Sample

Sulphite liquor

Enriched sulphite liquor

Washed yeast milk

Spent sulphite liquor

Dried yeast

Phosphoric acid a

Molasses + sulphite liquor (1:2) Molasses Water a

Wood chips

De foamer

Date of sampling

Dry mass %

Cd

8/4/87 29/1/88 2/11/88 17/11/89 8/4/88 29/1/88 2/11/88 17/11/89 8/4/87 29/1/88 2/11/88 17/11/89 8/4/87 29/1/88 2/11/88 17/11/89 8/4/87 29/1/88 2/11/88 17/11/89 8/4/87 29/1/88 2/11/88 17/11/89 8/4/87 29/1/88 2/11/88 17/11/89 8/4/87 29/1/88 2/11/88 17/11/89 8/4/87 29/1/88 2/11/88 17/11/89 8/4/87 29/1/88 2/11/88 17/11/89

19.90

< 0.11 0.55 0.40 0.71 < 0.11 0.55 0.40 0.60 2.13 3.15 3.14 3.31 0.33 0.25 0.14 0.17 0.84 1.96 1.04 3.40 0.14 0.12 0.11 0.23 0.03 0.21 0.11 0.02 < 0.02 < 0.002 < 0.001 0.003 0.19 0.16 0.22 0.16 0.01 < 0.02 < 0.01 < 0.01

18.53

17.15

12.11

92.00

34.72

60.80

95.94

34.43

~

Pb s

0.03 0.01 0.05 0.01 0.01 0.08 0.10 0.04 0.07 0.07 0.29 0.003 0.02 0.004 0.02 0.04 0.01 0.06 0.02 0.02 0.02 0.04 0.01 0.01 0.02 0.01

0.001 0.07 0.04 0.02 0.07

~

< 0.52 < 0.24 < 0.52 0.75 < 0.54 < 0.26 < 0.49 0.45 1.06 0.52 < 0.58 0.56 < 0.83 < 0.20 < 0.50 0.76 0.52 0.44 1.04 0.54 < 0.10 < 0.08 < 0.11 0.09 0.20 0.53 2.48 1.04 < 0.10 < 0.01 < 0.02 < 0.01 0.28 0.30 < 0.61 < 0.47 0.17 < 0.06 < 0.25 < 0.06

Hg s

0.10

0.13 0.15 0.06 0.08

0.06 0.10 0.06 0.06 0.19

0.03 0.02 0.15 0.16 0.12

0.17 0.09

0.05

~

s

0.038 0.023 0.002 0.016 0.018 0.025 0.004 0.012 0.263 0.059 0.003 0.035 0.083 0.017 0.003 0.017 0.073 0.046 0.022 0.027 0.001 0.001 0.001 0.007 0.017 0.009 0.004 0.003 0.011 < 0.001 0.002 0.002 0.089 0.155 0.035 0.014 0.010 0.001 0.001 0.119 b

0.017 0.001 0.001 0.006 0.006 0.013 0.000 0.004 0.141 0.003 0.001 0.003 0.025 0.005 0.001 0.001 0.001 0.001 0.002 0.001 0.000 0.000 0.001 0.003 0.005 0.003 0.000 0.002 0.007 0.001 0.001

0.024 0.015 0.016 0.002 0.002 0.001 0.001

85

CADMIUM, LEAD AND MERCURY LEVELSIN FEEDING YEAST

TABLE 5

(continued)

Sample

Cellulose

Non-bleached cellulose KOH a

Date of

Dry mass

Cd

sampling

%

K

Pb

s

8/4/87 29/1/88 2/11/88 17/11/89 17/11/89 18.00

< < < <

0.02 0.06 0.02 0.03 0.10 0.02

17/11/89

< 0.01

~

Hg

s

K

s

< 0.10 0,39 0.12 < 0,50 0.30 0.07 < 0,86

0.043 0.012 0.012 0.010 0.058

0.041 0.004 0.004 0.002 0.016

< 0.07

1.105

0.020

a m g ' k g - J of fresh matter. bDue to surprisingly high mercury levels, we show only the value of one measurement. The mercury content of this particular sample will be the subject of further method research.

Svobodov~i and Muzik~if (1984) found elevated lead levels only in a few samples of baker's yeast in Czechoslovakia. Similarly, low Pb and Hg levels were measured in our baker's yeast samples (Kpb = 0.13-0.19 mg P b - k g -t dry matter; xHg = 0.006-0.013 mg Hg. kg -~ dry matter). This corresponds with the finding of Bittel et al. (1977) that heavy metals in bread came mostly from flour and not from the water or the baker's yeast used in preparing bread. To locate the possible sources of Cd, Pb and Hg, selected interproducts and raw materials were analyzed; the results are summarized in Table 5. It would appear that the main source of Cd is sulphite liquor (0.40-0.71 mg Cd. kg-l), in which Cd enters from wood chips (0.16-0.22 mg Cd-kg-~). The amount of Cd in phosphoric acid (0.11-0.23 mg. kg -~) is very small considering the total quantity of the acid used in the technology. We consider the main source of Cd in the process to be the wood used as a raw material. We believe that the relatively high Cd level in wood corresponds to a general worsening of the environment in Czechoslovakia. Lead levels in the dry matter of the samples of the raw material were generally very low. Higher Pb levels in samples of the molasses and sulphite liquor collected on 2/11/88 suggested that the molasses could be a source of Pb. This was proved on 17/11/89, when the Pb level of the molasses sample was found to 1.04 mg. kg -~. Relatively high Hg contents in the sulphite liquor (up to 0.038 mg. kg -1) indicate that an important source of mercury may be the wood (up to 0.155 mg Hg. kg-~). The highest Hg level (1.105 mg. kg-1) was measured in a sample of KOH. The reason for this was the electroanalytical production of KOH on a mercury electrode.

86

J. CIBULKA ET AL

The high mercury level in the defoamer (0.119 mg.kg -1) sampled on 17/11/89 does not correspond to lower Hg levels measured in previous sampling (0.001-0.010 mg Hg. kg-~). It was learned that, at present, a defoamer (Unidan) made in Yugoslavia is being used, rather than a previously used defoamer (Struktol J-633) made in West Germany. ACKNOWLEDGEMENTS

The authors thank Dr. J. Sedlbauer, BIOCEL, Paskov for his help in sample collection and for providing information concerning the technology. We thank Dr. Z. Svatog and Dr. J. Rezni6kov~i for their help in sample analyses. REFERENCES Anonymous, 1986. Law collection No. 61/1986, Czechoslovakia. Anonymous, 1987. Law collection No. 117/1987, Czechoslovakia. Ahlers, J. and E. Rfsick, 1985. Influence of nitrilo-triacetic acid on Cd2÷-uptake by yeast. Int. Conference Heavy Metals in the Environment, Athens. Bittel, R., A. Fourcy, B. Godon and G. Mourioux, 1977. Transfer of heavy metals in the baking chain. Ann. Technol. Agric., 26, 2: 189-198. Burgerovfi, E., 1981. Mo~nosti vyu~iti kvasinek obohacen~ch mikroelementy v krmivfi~sk~ praxi. Sbornik VSZ Praha, PEF (~esk6 BudEjovice, 875: 275-283. (2ern~, S., 1988. Interakce a transformace n~kter~ch t~k~ch kov6 v p~E. Konference "T~.k~ kovy v ~ivotnim prostgedi", (~esk~ BudEjovice. Dr~ipal, J., 1989. Problematika cizorod~ch l~itek. Zprfivy CISVI3, c. 4, IV. ~tvrtleti: 7-20. Klement, V., 1987. OvEgeni produk~ni fiEinnosti kompletnich krmn~ch sm~si pro nosnice se za~azenim krmn~ch kvasnic vyroben~,ch v Paskov6 s obchodnim n~zvem Vitex. VSZ Brno, dipl. prfice, 27 s. R6sick, E., M. Mangir and E. Lochmann, 1986. Unterschiedliche Aufnahme von Cadmium in Saccharomyces- bzw. Rhodotorulazellen. Chemosphere, 15, 8: 981-983. Rossi, V., 1976. Proteins from petrol. Boll. Lab. Chim. Provin., 27, 5: 161-173. Svobodovfi, J. and V. Muzik~i~, 1984. Nage poznatky z kontroly vybran~,ch mikroprvkt~ v po~ivatinfich. Dny hygieny a v~,~ivy "Potrava jako faktor prosti~edi '', Karlovy Vary. Wolf, A., S. Hrub2~, D. Hrivn~ik, M. Sv~ibovfi et al., 1982. Hygienic evaluation of some untraditional protein sources. (~eskoslov. Hyg., 27, 2: 108-111.