Matti Viluksela

Relation between physicochemical properties of phenols and their toxicity and accumulation in fish

The 96-hr LC50 values of 21 substituted phenols for the guppy (Poecilia reticulata) were determined at pH levels 6-8 and related to the lipophilicity defined as log P from the 1-octanol/water system, and to the delta pKa value (pKa of phenol-pKa). Log P was the more important parameter and exhibited a good correlation with log(1/LC50) at pH levels. The contribution of delta pKa when introduced as a second parameter into the regression equation was dependent on the pH of water: at pH 6 it was positive but turned negative as the pH was raised to 8. If the LC50 values were corrected for ionization using an empirically formulated relation between toxicity and pH, the resulting regression equation could be used to predict the toxicity at any pH from 6 to 8. When corrected for ionization, log BCF (the bioconcentration factor) of 8 phenols was highly correlated with log P but not with delta pKa. The regression of log BCF on log P sufficed to explain the regression of toxicity on lipophilicity.

Factors affecting the absorption of phenolics and carboxylic acids in the guppy (Poecilia reticulata).

The rate of absorption of 17 phenols, anisoles, and carboxylic acids in the guppy (Poecilia reticulata Peters) was measured at pH levels from 3 to 9. The rate was directly proportional to the concentration, and the compounds did not interfere with each others absorption. The primary route of uptake was across the gill epithelium, but 25-40% of the total amount penetrated across the skin. When the fish were exposed at a pH low enough to prevent ionization of acidic compounds, the initial rate of uptake increased with lipophilicity up to a partition coefficient of about 10(4). Above this point, the absorption rate did not correlate with lipophilicity indicating that the uptake rate of the most lipophilic compounds was limited by the unstirred water layers. The effect of lipophilicity on absorption accounts for about half of the effect found in toxicity and bioconcentration. The absorption rate of acids declined with pH rising, but did not follow changes in the concentration of nonionized acid. The slopes of the absorption rate vs pH curves were distinctly less steep than the slope of the dissociation curve. In addition, the curves of the most lipophilic acids showed a shift to the right, which can be ascribed to the unstirred layers on the surface of the epithelia.

Hepatic effects of a highly purified 2,2′,3,4,4′,5,5′-heptachlorbiphenyl (PCB 180) in male and female rats

PCB 180 (2,2,3,4,4,5,5-heptachlorobiphenyl) is a persistent and accumulating polychlorinated biphenyl abundantly present in food and the environment. In this study, we used highly purified PCB 180 (dioxinlike impurities: 2.7 ng TEQ(WHO)/g PCB 180) in a 28-day toxicity study in young adult Sprague-Dawley rats. Male and female rats were given total doses of 3, 10, 30, 100, 300, 1000 or 1700 mg/kg b.w. PCB 180 by gavage. Increased liver weights were observed at ≥ 300 mg/kg b.w. in males and females. No increases in serum ALT or ALP activities were found. A significant increase in liver pentoxyresorufin O-dealkylase (PROD) activity was found in males at ≥ 10 mg/kg b.w. and in females at ≥ 30 mg/kg b.w. In both genders, a significant induction of hepatic 7-ethoxyresorufin O-deethylase (EROD) activity was also observed in males at ≥ 10 mg/kg b.w. and in females at ≥ 300 mg/kg b.w. Western blotting showed that mainly cytochromes P450 (CYPs) 2B1/2 and 3A1 were induced while slight effects were seen on CYP1A1, CYP1A2 and CYP1B1. However, no induction of CYP1A1, 1A2 and 1B1 was found on the mRNA level, except for a slight effect in females at 1000 mg/kg b.w. Furthermore, hepatic UDP-glucuronosyltransferases (UGTs) 1A1 and 1A6 were markedly induced in males and slightly induced in females. The hepatic concentrations of apolar retinoids were decreased in males at ≥ 30 mg/kg b.w. and in females at ≥ 300 mg/kg b.w. Taken together our findings show that pure PCB 180 leads to hepatic changes in a dose range which did not cause CYP1A1 induction but causes centrilobular liver hypertrophy, affects drug-metabolizing enzymes involved in the metabolism of exogenous and endogenous substrates and leads to changes in liver retinoid levels. A benchmark dose (BMD) approach is presented in order to model lowest effective dose levels for these effects. Comparison of PCB 180 liver level related to BMDL₅ for hepatic hypertrophy in rats with human data on total hepatic PCB levels in individuals without history of specific exposure suggests a relatively small margin of tissue burden in the range of 37-fold. Our results show that the highly pure non dioxin-like PCB 180 exerted strong effects different to dioxin-like compounds and that the low TEQ contamination allowed a characterization of the PCB as non-dioxinlike.

Studies on the contact sensitizing activity of dithranol (anthralin) and 10-butyryl dithranol (butantrone)

The contact sensitizing activity of dithranol and butantrone (10‐butyryl dithranol) was studied in 3 animal models: the guinea pig maximization test (GPMT). the closed patch test (CPT), and the mouse ear swelling lest (MUST) in 2 different mouse strains. In the GPMT. both dithranol and, to a greater extent, butantrone showed sensitizing potential. Because butaintrone was less irritant, the concentrations used were 10 x higher than those of dithranol. In the CPT, only butantrone was slightly positive. In the MEST. with both CF‐1 and Balb/c mice, dithranol caused less swelling of the test ear after challenge than butantrone. According to the evalution criteria of the MEST, only butantrone caused sensitization in 50% of the CF‐1 mice and in 40% of the Balb/c mice. Thus, the GPMT was the only test which indicated the minor contact sensitizing potential of dithranol. On the other hand, the 10‐butyryl analogue of dithranol showed undoubtedly stronger contact sensitizing potential than the parent compound in all tests. Therefore, as compared to dithranol, an increased risk of sensitization should be considered.