Combined Actions and Interactions of Chemicals in Mixtures

kidneys at the LONEL, and a dose-dependent increase in kidney weight and
number of epithelial cells in the urine at the NONEL and the LONEL. The males
treated with a single agent showed slightly increased kidney weights, and/or slight
histopathological changes in the kidneys at the LONEL, and (with d-limonene
only) epithelial cells in the urine at the NONEL and LONEL. In females, renal
changes induced by the combination were not more severe than those observed
with individual compounds. No adverse changes attributable to treatment were
observed in rats fed the combination at one-quarter of the NONEL. The authors
concluded that combined exposure to the four nephrotoxins at their individual
NONEL did not constitute an obviously increased hazard, indicating absence of
clear additivity and synergistic interaction, whereas at the LONEL clearly
enhanced renal toxicity occurred in males, although not in females (Jonker et al.
1993, Feron et al. 1995a).
5.3.2 Nephrotoxicants with similar mode of action
In a subsequent study the additivity assumption (dose addition) was tested, using
the similarly acting nephrotoxicants tetrachloroethylene (Tetra), trichloroethylene
(Tri), hexachloro-1,3-butadiene (HCBD) and 1,1,2-trichloro-3,3,3-
trifluoropropene (TCTFP) (Jonker et al. 1996). The compounds were given to
female rats by daily oral gavage for 32 days either alone, at the LONEL and
NONEL (= LONEL/4), or in combinations of four (at the NONEL and LONEL/2)
or three (at the LONEL/3), see Table 5.3.21.
Relative kidney weight was increased on exposure to the individual compounds at
their LONEL and, to about the same extent, on combined exposure at the NONEL
or the LONEL/3.The other end-points studied (histopathology, concentrating
ability, urinary excretion of glucose, protein and marker enzymes, and plasma
creatinine and urea) were not or only scarcely affected upon combined exposure at
the NONEL or LONEL/3. As assessed by the effect on kidney weight, the renal
toxicity of the mixtures corresponded to the effect expected on the basis of the
additivity assumption. (Feron et al. 1995a, Jonker et al. 1996).
Table 5.3.2.1. Four-week oral toxicity study in female rats with mixtures of nephrotoxicants
having similar mode of action
Treatment (mg/kg bw/d) Total doses in toxicity
units
Control: corn oil 10 ml/kg bw/d
Individual compounds at NONEL e
Tetra a 600 mg/kg bw/d ¼
Tri b 500 mg/kg bw/d ¼
TCTFP c 1.5 mg/kg bw/d ¼
HCBD d 1.0 mg/kg bw/d ¼
Individual compounds at LONEL f
Tetra 2400 mg/kg bw/d 1
Tri 2000 mg/kg bw/d 1
TCTFP 6.0 mg/kg bw/d 1
HCBD 4.0 mg/kg bw/d 1
Combination of all 4 compounds
At NONEL 1
At LONEL/2 2
Combination of 3 compounds
Tetra + Tri + TCTFP at LONEL/3 1
Tetra + Tri + HCBD at LONEL/3 1
Tetra + TCTFP + HCBD at LONEL/3 1
Tri + TCTFP + HCBD at LONEL/3 1
a Tetra = tetrachloroethylene
b Tri = trichloroethylene
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