88 Articles of general interest-Fd Cosrtrc~r. To.\-icol. Vol. 17. No. I

tenance of a steady fluoride balance depended on the existence of a store of fluoride in the gut. Faecal ex- cretion of fluoride amounted to some 85% of the in- take. Removal of fluoride from the extraceMar pool into the bone compartment was about three times more rapid than its removal into the urine. Some evi- dence was obtained that the rabbit’s response to fluoride is linear over a wide range of doses. In anaes- thetized rats, the fractional clearance of fluoride by the kidney was not altered by changes induced in the rate of urinary flow or in fractional chloride clear- ance by the diuretics frusemide and acetazolamide (Whitford et al. Am. J. Physiol. 1976, 230, 527) but showed a strong dependence on urinary pH. Reab- sorption of fluoride was more than 95% complete over the pH range 5.0-5.6, but fluoride clearance rose to 70% when the urinary pH reached 78-80. There was evidence that the increase in fractional fluoride clearance seen during mannitol-induced diuresis was associated with an increase in urinary pH. It is sug- gested that while fluoride reabsorption can occur along the entire length of the nephron, it only occurs in the distal part of the tubule under acidic condi- tions.

In rats maintained on a high fluoride intake (34 ppm fluoride in the food and 50 ppm in the water) for 28 days and then given a low-fluoride diet (0.21 ppm) and distilled water, there was a 12-fold in- crease in fluoride uptake by the humeri during the 4-week high-intake period, more being taken up by the epiphyses than by the diaphyses (Singer et al. Proc. Sot. exp. Biol. Med. 1976, 151, 627). After the 3-week fluoride-depletion period, however, the skele- tal fluoride content had fallen by only 7.7%. These results are not inconsistent with those demonstrated in man by Spencer et al. (J. appl. Physiol. 1975, 38, 282). During the period of high-fluoride treatment, there was a significant increase in the fluoride levels of the plasma, muscle and liver, but these concen- trations returned to baseline values within 3-7 days of the transfer to the low fluoride intake. These authors report evidence from studies using ionized radioactive fluoride that muscle and liver contain bound fluoride, which is not immediately available for exchange with fluoride ions.

[P. Cooper-BIBRA]

DI-(2-ETHYLHEXYL) PHTHALATE AND THE BLOOD

Significant quantities of di-(2-ethylhexyl) phthalate (DEHP) have been found in blood preparations in- tended for transfusion and stored in PVC packs (Cited in F.C.7: 1971,9, 910), and it was demonstrated some years ago that when DEHP migrates from stor- age bags plasticized with it, the bulk of it becomes concentrated in the plasma-lipoprotein fraction of the stored blood (ibid 1973, 11, 914).

Rubin & SchilTer (Transfusion 1976, 16, 330) have reported on six leukaemic patients who were given platelet infusions from packs made of a vinyl plastics material. Each infusion took 20-30 minutes with the exception of one which lasted for 1 hour. Blood samples were taken before and immediately after the infusion and then at 15-minute intervals for 1 hour. The concentration of the plasticizer in the stored platelets was such that the total DEHP administered to these patients ranged from 26 to 82mg. Peak plasma concentrations of DEHP, found at the end of the infusion, ranged from 0.34 to 0.83 mg/lOOml and averaged about 0~02mg/1OOml plasma for each milligram DEHP administered per square metre of body surface. Thereafter the blood concentration of DEHP fell exponentially with a mean disappearance rate of 2.83%/minute. giving a mean half-life of DEHP in blood of 28 minutes. No striking difference in DEHP half-life was apparent in two patients showing mild hepatic-function abnormalities. In two patients whose urinary excretion of DEHP metabolites was studied, 55.9 and 40mg of DEHP equivalents, or 90 and 60% of the dose, respectively, appeared in the urine in the 24 hours following the infusion. Since, before this platelet infusion, these two patients were excreting 9.0 and 13.8 mg of DEHP equivalents daily (possibly, at least in part, as a result of previous transfusions), the

excess excretion of DEHP apparently attributable to the platelet infusion represented about 75 and 40x, respectively, of the administered plasticizer.

Relatively rapid clearance and excretion of DEHP was thus demonstrated in these patients, and the wide use of preparations of this type as well as the results of animal testing have so far provided little evidence of adverse effects. Nevertheless it is important to remember that patients given blood transfusions may be suffering from a wide variety of abnormalities and may be more susceptible than healthy people to the effects of foreign chemicals. The situation is further complicated by the fact that the pattern of tissue dis- tribution has been shown to vary with the physical state of the DEHP. Rubin & Schulz (Toxic. appl. Pharmac. 1974, 29, 143) demonstrated, for example, that the physical state of the ester in iv-administered solutions greatly affects the rapidity of its clearance from plasma and the extent of its retention in the liver. While present evidence indicates that the DEHP present in vinyl-stored blood products is in a solubi- lized state rather than in the form of suspended oil droplets (Rubin & Schiffer, lot. cit.), this situation is not reflected in much of the experimental toxicity and distribution data available. This is because the plasti- cizer’s low solubility in water has led to the use of solubilizing agents or physical techniques, such as sonication, in the preparation of test solutions. Solu- bilization with Tween 80, which has been used in some studies, has been shown to cause a marked in- crease in the acute toxicity of iv doses of DEHP (Schulz, Fedn Proc. Fedn Am. Sots exp. Biol. 1974, 33, 234).

To avoid such complications, Waddell ef al. (Toxic. appl. Pharmac. 1977, 39, 339) incorporated into an

Articles of general interest-FL/ Cosr~rt. Tauicol. Vol. 17. No. I 89

autoradiography study a procedure designed to pro- vide a test solution containing DEHP in the physical state in which it would be likely to be encountered in blood stored in plastics bags. By immersing DEHP labelled with 14C in the carbonyl group in sterile mouse plasma. for 78 days at 22°C they achieved a concentration of 2.293 mg DEHP/ml. Intravenous injections of I ml of this plasma were given to adult male mice, which were anaesthetized and frozen for whole-body autoradiography after 1, 3, 9 or 24 hours or 7 days. Others, injected with the labelled DEHP 30 minutes after ligation of both renal pedicles, were subjected to autoradiography 1 or 3 hours after the injection. The responses of germ-free mice to these treatments were compared with those of conventional animals. In all the mice there was rapid accumulation of radioactive label in the kidney and liver, but not in other organs. This was demonstrated 1 hour after the injection, but by 3 hours considerable elimination into the urine, bile and intestine had occurred and elimination was virtually complete within 9 hours, except in the mice with ligated kidneys. These showed a more prolonged retention of radioactivity and a more scattered distribution in the blood and extra- cellular fluids.

Attachment of DEHP to protein constituents of human plasma, with physical alteration, has been demonstrated by Stern et al. (ibid 1977, 41, 507), in further attempts to define the form of the DEHP

actually encountered by patients given blood trans- fusions from PVC packs. In human plasma stored at room temperature for IO days in PVC packs plasti- cized with [14C]DEHP, they demonstrated that DEHP formed a non-particulate diffusion complex and that the extent of migration was determined not by the plasma lipid content but by the total protein concentration. In non-particulate solutions prepared by the careful addition of ethanolic DEHP to plasma, a large proportion of the DEHP was shown to be bound to the Q- and P-globulins. When the diffusion complex of [14C]DEHP was injected into the tail vein of rats, the second phase of 14C half-life in the blood was shorter than when a complex formed from an ethanolic or Polysorbate-80 solution was used, organ retention was reduced and excretion was more rapid, at least initially. When included in the perfus- ing fluid for an isolated rat-liver preparation, the pro- tein diffusion complex of DEHP was metabolized and rapidly excreted in the bile.

These findings provide further evidence that the physico-chemical reactions of DEHP with plasma are complex, and that when toxicity studies of this plasti- cizer are undertaken in connexion with its presence in transfused blood, the non-particulate complex, which is the actual blood contaminant, should be used, rather than other solubilized or particulate forms.

[P. Cooper-BIBRA]

EVIDENCE OF A SAFE LEVEL OF TDI

Toxicology cannot class toluene diisocyanate (TDI) as one of its success stories. In spite of considerable scientific interest, the mechanism underlying its toxic action still remains elusive (Cited in F.C.7: 1972, 10, 730; ibid 1976. 14. 218; ibid 1977. IS. 365). The inability of the toxicologiSt to define an acceptable atmospheric concentration of TDI is a more practical disappointment.

Among recent additions to the TDI literature is a report by Wegman et al. (Br. J. ind. Med. 1977, 34, 196) on a follow-up of an earlier investigation of workers involved in the production of polyureth- ane. The original study (idem, J. occup. Med. 1974, 16, 258) demonstrated that exposure to TDI resulted in an acute reduction in pulmonary function. The same workers were re-examined 2 years later to assess the chronic effects of TDI. Only 63 of the 112 workers originally studied were still employed and therefore available for examination, but the pulmonary func- tion of the retested and lost groups of workers was comparable in 1972 and there was little evidence of a selection bias in the restudied group.

TDI levels at the workplace were determined five times during the 2 years between the two investiga- tions and were found to be stable. The workers were divided into three groups of approximately equal size: those exposed to TDI levels in excess of 0.0035 ppm, those exposed to between 0.002 and 0.003 ppm TDI. and those exposed to levels below 0+)015 ppm.

Although the incidence of subjective symptoms of pulmonary disorder was similar in all three groups, the prevalence of coughing and phlegm increased with increasing exposure and there were variations in per- formance in pulmonary-function tests. The group exposed to the lowest levels of TDI had a 2-year change in forced expiratory volume (FEV) within t.he expected limits for a normal population, but in the other two groups, loss in FEV increased with increas- ing exposure. Even when all possible contributory fac- tors were considered, including age, smoking habits and lung size, the differences between the groups were still significant, and it was concluded that a loss of pulmonary function occurred at TDI exposures of

0.0035 ppm with a possibility that exposures as low as 0.002 ppm were having some effect.

Wegman er al. (1977, lot. cit.) stressed the impor- tance of measuring the factory levels of TDI as well as length of work service in any prospective study of the effects of this particular monomer. If length of service had been adopted as the sole index of expo- sure, no significant correlation would have been found between exposure and reduction in FEV. These authors also noted the possible complications intro- duced by the welldocumented acute effects of TDI; at high exposures FEV decreases over every work- shift, whereas at lower levels, acute loss occurs on the first day of a working week. Because of this, it was emphasized that lung function should be exam-