POLYCHLORINATED BIPHENYLS (PCB's) - Environmental Implications

BIO-ACCUMULATION AND BIO-TRANSFORMATION OF PCB's

PCB's are persistent and stable compound and they do not degrade rapidly and are passed up to aquatic food chain in increasing level. This phenomenon is known as bioaccumulation. PCB's accumulate in tissues of almost all organisms, because of their high lipid solubility and slow rate of metabolism and elimination. They accumulate preferentially in fat-rich tissues

Uptake by micro-organism of both pure chlorinated biphenyl isomers and commercial PCB mixtures is rapid, and high bio-concentration factors are achieved. According to some studies PCB congeners with higher levels of chlorination are taken up preferentially, in the majority of studies, all PCB's appear to be taken up equally. Uptake by micro organism is true absorption; adsorption onto the surface of the organisms represent little of the uptake. Since, resistant forms, of micro-organisms take up less PCB's than sensitive forms and dead cells accumulate more PCB's than live cells, there is some capacity to exclude the compounds.

Uptake of PCB's into plants from soil is positively correlated with the soil concentration of the PCB's. The accumulation capacities of roots are more than the stems and foliage. Lower chlorinated congeners of the PCB's are taken up more by the plants, probably because of their greater mobility in the soil.

The PCB's uptake by plants is influenced by following factors:
  • The PCB's concentration in the soil.
  • CPCB's uptake between plant species are different, some species absorb more PCB's than others.
  • Most of the PCB's in roots may, in fact, be adsorbed on the surface and not actually taken up.
  • There is a general trend of increasing PCB content with decreasing chlorination for pure PCB congeners.
  • The amount of chlorination seems to have an effect on the mobility of PCB's within plant parts. The lower chlorinated PCB's have been reported to be more mobile in soils than highly chlorinated PCB's.
Fish of all life stages absorbs PCB's readily from water. PCB's with greater chlorination are more readily taken up and retained. PCB's body burden tends to increase with age of the fish and levels are higher in fish with greater lipid content. Depending on the species, habitat, and behavior, PCB's can be taken up from water, sediment or food to different degree.

In Birds, the PCB's are taken up from contaminated food or water and concentrated in the fatty tissues. PCB's of higher chlorination levels are accumulated to a greater extent. Egg-laying females can transfer substantial amounts of PCB's from body tissues to the eggs. Redistribution of PCB's residue occurs on starvation (starvation is significant during the migration of birds in the wild). Most critically, PCB residues in the brain increase during starvation and this may kill the birds without further intake of PCB's.

                                        Yusho Accident, 1968 - Japan
In June, 1968 patients appeared at the Dermatology clinic of Kyusthu University Hospital, Fukuoka, Japan suffering from chloracne. After few clinical, chemical and epidemiological investigations, it was found that the disease originated from the consumption of a batch of rice oil supplied in February, 1968; the disease was called Yusho (rice oil disease). This rice oil was found contaminated with Kanechlor 400, a 48% chlorinated biphenyl, at 2000-3000 mg/kg, which entered the oil through a leak in the heat exchanger. Chlorinated dibenzofurans at 5 mg/kg were found in three samples of toxic rice oil that contained PCB levels of about 1000 mg/kg (Nagayama et.al., 1976).

The earliest symptoms of PCB's exposure were enlargement and hyper-secretion of the Meibonian glands of the eyes, swelling of the eyelids and pigmentation of the nails and mucous membranes, occasionally associated with fatigue, nausea and vomiting. This was followed by hyperkeratosis and darkening of the skin with follicular enlargement and acneform eruptions. These skin changes were most often seen on the neck and upper chest, but in severe cases, extended to the whole body.

Biopsy skin samples showed hyperkeratos i.e. dilation of the follicles, and an accumulation of melanin in the basal cells of the epidermis; melanin granules have also been observed in biopsy samples of the conjunctiva, oedema of the arms and legs was also observed in some patients. The majority of the patients were found to have respiratory symptoms and suffered from chronic bronchitis like disturbance, that persisted for several years.

Yusho patients did not appear to suffer from central nervous effects, but some complained of numbness of the arms and legs. Nuco-cutaneous signs had decreased year-by-year, but neurological signs, respiratory signs and symptoms and various complaints, as general fatigue, anorexia, abdominal pain and headache, had become more prominent among the patients.



                                        Yusho Accident, 1968 - Japan
A similar incident to Yusho accident occurred in Taiwan in 1979, and by the end of 1980, the number of affected persons were found 1843. The incident has been referred to as Yu-Cheng (Chang et.al., 1980a, b; Chen et.al., 1980). The accident had occurred due to the consumption of rice bran oil contaminated with PCBs that was used as a heat transfer medium in the manufacture of the oil. PCB intake was estimated to be 0.7-1.84 g and blood PCB levels ranged from 3 to 1156 µg/litre. The formation and hypersecretion of the meibonian glands occurred in patients, whose blood PCBs concentration was above 40 µg/litre.

The common symptoms noticed were heavy pigmentation of conjunctiva, abnormal cystic acneiform eruptions and follicular accentuation, skin and nail pigmentation, swelling of the eyelids and increased discharge from the eyes, headache, nausea, and numbness of the limbs. The major blood disorders were decreased hemoglobin concentration, erythrocyte conc., gamma-immunoglobin and increased white blood cell counts.