Arch. Toxicol. 41, 179-186 (1978) Archives of

TOXICOLOGY �9 Springer-gerlag 1978

Transfer of 2,4,5,2',4',5'-Hexachlorobiphenyl and 2,2-bis-(p-Chlorophenyl), 1,1,1 -Trichloroethane (p,p'-DDT) from Maternal to Newborn and Suckling Rats

Mitsuru Ando

Environmental Health Sciences Division, National Institute for Environmental Studies, P.O. Yatabe, Ibaraki 300-21, Japan

Abstract. Pregnant rats were given a small dose of 14C-2,4,5,2',4',5'-hexachloro- biphenyl (HCB) and 3H-DDT intraperitoneally. The transfer of HCB and DDT through the placenta and milk was then investigated. Transfer through the pla- centa was 2.7 and 1.5% (respectively) of the initial doses; transfer through milk was 39.2 and 21.5%. HCB is obviously more transferable than DDT through the placenta and milk, the ratio of the amount of HCB transferred through milk to the amount transferred through the placenta agrees with that for DDT.

Concentrations of HCB and DDT in the whole suckling rat increases rapidly and is similar to the sigmoidal growth curve and change in lipid concentration. Therefore, the concentrations of the chemicals in the maternal tissue generally decrease in comparison with those of nonpregnant rats.

Key words. Chlorinated hydrocarbons - Hexachlorobiphenyl - PCB - DDT - Transfer.

Introduction

PCB has been one of the most useful industrial products since the 1940s, but be- cause it resists chemical degradation, it has polluted the global ecosystem (Jensen, 1972; Jansson et al., 1975). PCB poisoning occurred in western Japan in 1968. Thousands of people who consumed rice bran oil contaminated with Kanechlor-400 suffered from chloracnelike skin eruptions (Kuratsune et al., 1971). Recently, PCB has been found in normal human tissue and milk (Jensen and Sundstr6m, 1974; Masuda et al., 1974).

DDT was introduced as an insecticide after World War II. Its various toxic effects have been reported by many investigators (Laug et al., 1950; Hart and Fout, 1965; Kimbrough et al., 1971; Hayes, 1975). As DDT has also proved resistant to chemical degradation, it has accumulated widely in the environment and in human beings (Jensen et al., 1972; Brown and Chow, 1975).

Send offprint requests to: Mitsuru Ando (address see above)

0340-5761/78/0179/$ 01.00

180 M. Ando

It has been repor ted tha t ch lor ina ted hyd roca rbons , such as P C B and D D T , are

t ransfer red to the fetus th rough the p laccen ta (Cur ley et al., 1969) and to the baby

th rough milk (Hayes , 1975; Takag i et al., 1976). I t is therefore necessa ry to es t imate

the extent o f P C B and D D T transfer t h rough p lacen ta and milk.

Techn ica l p roduc t s o f P C B involve the mix ture o f m a n y isomers . M o s t investi-

gat ions o f P C B have been carr ied out using industr ial p roduc t s (Aroch lo r , Kane -

chlor etc.). Therefore , it is desirable to invest igate the na ture o f each P C B isomer , its

toxic effects, metabol i sm, and t ransfer rate.

In the present paper , the t ransfer rate o f 2 ,4 ,5 ,2 ' ,4 ' ,5 ' -hexachlorobiphenyl ( H C B )

and o f p,p'-DDT f rom mate rna l to newborn rats is s tudied and discussed.

Materials and Method

Female Wistar rats weighing 198-230 g were used in this study. The female rats were mated with males, and the day when the sperm was first found in the vaginal smear was counted as the day of conception (and termed day 0 of pregnancy). The rats were divided into four groups: In the three pregnant rats of group I, transfer of HCB and DDT through the placenta was investigated. Group II consisted of six nonpregnant rats, and group III of six pregnant rats, used to investigate the transfer of HCB and DDT through milk. Four nonpregnant rats (group IV) were used to compare data with group III.

Radioactive 14C-HCB (44.4 mCi/mmol, NEN Co.) and 3H-DDT (15.2 mCi/mmol, NEN Co.) were dissolved in soybean oil. Every rat received 14C-HCB (2.1 ~Ci/kg body weight) and 3H-DDT (83 ~Ci/kg body weight) intraperitoneally, and the rats were then placed in a separate metabolic cage until day 18 of gestation. They were fed on laboratory chow and water ad lib. The weights of the rats were recorded every 2 or 3 days before birth and once a week thereafter.

The rats of groups I and II were killed on the day of birth. From each of three litters of group III, two rats were killed on the day of birth, and on the 4th, 9th, 12th, 14th, and 16th postnatal days. One maternal rat was killed 12, 14, and 16 days after giving birth. Three other maternal rats of group III, their newborn, and four nonpregnant rats of group IV were killed on the 16th postnatal day.

All rats were killed by heart puncture while under ether anesthesia. Liver, kidney, and adipose tissue were removed, rinsed with physiological saline, weighed, and stored at --20 ~ C. After adding an equal volume of physiological saline, liver was homogenized in a 30-ml Potter-Elvehjem glass homoge- nizer in an ice bath, placed in screw-capped test tubes, and stored at - 2 0 ~ C.

Newborn and suckling rats were killed while under ether anesthesia. Each rat was homogenized quickly in an universal homogenizer in an ice bath after weighing and adding an equal volume of physiological saline. A part of the homogenized sample was used to analyze the concentration of lipids and radioactivity of 14C and 3H.

14C-HCB and 3H-DDT were extracted according to the method of Dale et al. (1970). 14C-HCB and 3H-DDT were extracted from adipose tissue after 48 h, and from liver, kidney, and blood after 24 h. The solvent of the extracted 14C-HCB and 3H-DDT was evaporated in a rotary evaporator. ~4C- HCB and 3H-DDT were then dissolved in a toluene scintillator (ppo 4 g, popop 0.1 g, toluene 11) and measured in a Beckman liquid scintillation spectrometer. The radioactivity was expressed as disintegra- tions of 14C or 3H per min per g of tissue. Lipid was extracted from liver by a chloroform-methanol mixture (2 : 1) and determined by the method of Bragdon (1960).

Results

Newborn and Suckling Rats

The g rowth rate o f suckl ing rats gives a typical s igmoid curve, as does the increase

in concen t r a t ion o f lipid in newborn and suckl ing rats. Tab le 1 shows the rad ioac t iv-

Transfer of HCB and DDT Through Placenta and Milk 181

Table 1. Body weight, lipid concentration, and radioactivity in newborn and suckling rats (Mean + SD)

Days after Body weight Lipid birth (g) concentration

(mg/g)

Radioactivity per gram of rat (g)

14C-HCB 3H-DDT (x 103) (X 104)

0 6.05 + 0.65 32.9 + 6.8 0.36 + 0.18 0.81 +0.04 4 9.63 _+ 1.44 51.9 + 13.3 1.13 + 0.33 2.71 + 0.71 9 20.9 + 2.8 91.6 + 11.0 1.25 + 0.15 2.96 + 0.37

12 31.7 + 1.5 105.3 + 11.1 1.64 + 0.17 3.80 + 0.38 14 35.5 + 1.1 124.0 + 5.4 1.54 + 0.14 3.90 _+ 0.06 16 38.3 _+ 2.2 117.1 + 2.3 1.92 + 0.10 4.23 + 0.21

Table 2. The radioactivity of 14C-HCB and of 3H-DDT per gram of lipid, and the radioactivity in the whole body of newborn and suckling rats (Mean + SD)

Days Radioactivity per gram Radioactivity in whole body after of lipid (g lipid) of rat (rat) birth

14C-HCB 3H-DDT 14C-HCB 3H-DDT (x 103) (x 105) (x 103) (x 105)

0 8.65 _+ 4.03 1.81 _+ 0.74 2.21 + 1.26 0.51 + 0.29 4 23.1 _+ 9.5 5.52 + 2.13 10.7 + 2.1 2.57 + 0.48 9 13.9 +_ 3.3 3.27 _+ 0.66 26.0 + 3.1 6.20 + 1.13

12 15.5 _+ 1.3 3.61 _+ 0.28 52.0 _+ 6.1 12.1 + 1.7 14 12.4 + 0.9 3.15 + 0.18 64.7 + 2.5 16.4 + 0.8 16 16.4 + 1.0 3.61 + 0.21 72.3 + 3.7 16.0 + 1.0

ity of 14C-HCB and of 3H-DDT per g of the suckling rats; it was found to increase gradually until reaching a saturation level. HCB and D D T behave similarly in this respect.

Table 2 shows the radioactivity of 14C-HCB per g of lipid in the suckling rats. The peak of the radioactivity is on the 4th day after delivery and from the 9th day the radioactivity remains virtually constant. Similar results are obtained with 3H- DDT. Table 2 also shows the increase in the total radioactivity of 14C-HCB and of 3H-DDT in the whole body of the suckling rats. The increase of the total radioactiv- ity is represented by a sigmoid curve which is similar to the curve for body weight.

The relationship between the total radioactivity of 14C-HCB in suckling rats and the body weight is shown by Figure 1, from which a linear relationship is obvious. A similar result is obtained with 3H-DDT.

182 M. Ando

o

xlO ~

'~ 10.

'S

m

y

~ 2

o o o o

o o

o o

10 20 30 40 50 6'0

body w e i g h l of r a t ( gJ

Fig. 1. The relationship between the total radioactivity of 14C-HCB in the whole body of suckling rats (y- axis) and their body weight (x-axis)

Maternal Rats

Table 3 shows the average weight of the whole animal and that of the liver and kidneys. There is no significant difference in the weights between groups I and II, but the liver and kidney weights of nursing rats (group III) are significantly greater than those of nonpregnant rats (group IV).

In blood, the concentration of lipids does not vary between the groups. The concentration of liver lipids is higher in rats after delivery than in nonpregnant rats. Otherwise, the concentration of liver lipid in nursing rats is lower than that in non- pregnant rats.

Table 4 shows the radioactivity of 14C-HCB in liver, blood, and kidney. The radioactivity of 14C-HCB in the blood of pregnant and nursing rats is evidently lower than in that of nonpregnant rats. The radioactivity of laC-HCB in the liver and kidneys of nursing rats is significantly lower than that of nonpregnant and of preg- nant rats.

Table 5 shows the radioactivity of aH-DDT in liver, blood, and kidney. The radioactivity of 3H-DDT in the blood of pregnant and nursing rats is lower than in that of nonpregnant rats. The radioactivity of 3H-DDT in the liver and kidneys of nursing rats is significantly lower than in the liver and kidneys of nonpregnant and pregnant rats. This result is similar to that found with HCB.

From the result described above, it is obvious that the radioactivity of ~4C-HCB or 3H-DDT in organs of maternal rats decreases after delivery and during nurs- ing.

Discussion

Several investigations have shown that the metabolism of fat-soluble chlorinated hydrocarbons such as PCB and DDT is related to lipid metabolism (Ando, 1977; Dale et al., 1962; Lambert and Brodeur, 1976). The tranfer of chlorinated hydrocar-

Tab

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. A

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21

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1.68

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76

2.38

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92 a

1.88

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57

0.64

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of

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(x

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(x

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. R

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of

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of

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(x 1

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(x 1

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(x 1

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(•

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3.67

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I 0.

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O

Transfer of HCB and DDT Through Placenta and Milk 185

son and Mol, 1968). However, most studies have been performed with technical products o f PCB (the mixture of many kinds of PCB isomers); few experiments have been made with single PCB isomers (Peterson et al., 1976).

One of the most typical isomers of PCB is 2,4,5,2',4' ,5'-hexachlorobiphenyl (HCB). From the present studies, it is obvious that HCB and p ,p ' -DDT behave similarly with respect to their excretion and placental transfer.

The amount of HCB and D D T transferred from mother to newborn and suck- ling rats can be calculated as a percentage of the initial dose. HCB and D D T pass through the placenta in the amounts of 2.7 and 1.5% respectively, and through the milk by 39.2 and 21.5% respectively. The ratio of HCB transferred through milk to that transferred through the placenta is 14.6, while in the case of D D T it is 14.4. It is obvious that HCB is more easily transferred through the placenta and milk than DDT.

The concentration of HCB and D D T in maternal blood slightly decreases owing to the placental transfer of the chemicals. As the amount of HCB and D D T trans- ferred through the placenta is minute, the concentration of these chemicals within the maternal tissues does not change significantly as a result of placental trans- fer.

The transfer of HCB and D D T through the milk is sufficient to increase the total concentration of the chemicals in suckling rats. Therefore, the concentration of HCB and D D T within the maternal tissues does decrease significantly during nursing.

From the data presented, it is obvious that the concentration of HCB and D D T in maternal tissues generally decreases in comparison with that of nonpregnant rats.

Acknowledgements. My thanks are due to Prof. I. Wakisaka for much helpful discussion and encour- agement. I am also indebted to Dr. M. Sameshima for helpful suggestions.

References

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Received January 10, 1978