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In a study in which male rats have been exposed to 0,20, 60, 200, 600 and 2000 mg di(isononyl)phthalate (DINP)/kg diet for 2 weeks, body weight and liver weight and a number of enzyme parameters (palmitoyl coenzyme-A oxidase (PCO), enoyl coenzyme-A hydratase (ECH), carnitine acetyl transferase (CAT) and lauric acid hydroxylase (LAH)) have been determined in liver homogenates which are related with peroxisome proliferation. No effects have been observed on both liver and body weight. PCO, CAT and LAH, showed no effect at 200 mg DINP/kg diet, corresponding with 18.2 mg/kg b.w./day. ECH appeared to be the most sensitive parameter with a dose-without-effect of 60 mg DINP/kg diet, corresponding to 5.7 mg DINP/kg b.w./day. This value of 60 mg/kg diet has been defined as overall no-observed-effect-level for DINP in this experiment.

In a study in which male rats have been exposed to 0, 20, 60, 200, 600 and 2000 mg di(isodecyl)phthalate (DIDP)kg diet for 2 weeks, body weight and liver weight and a number of enzyme parameters (palmitoyl coenzyme-A oxidase (PCO), enoyl coenzyme-A hydratase (ECH), carnitine acetyl transferase (CAT) and lauric acid hydroxylase (LAH) have been determined in liver homogenates which are related with peroxisome proliferation. No effects have been observed on liver and body weight. CAT appeared to be the most sensitive parameter with a dose-without-effect (DWE) of 60 mg DIDP/kg diet, corresponding with 5.6 mg DIDP/kg b.w./day. The other enzyme parameters PCO, ECH and LAH showed no effect at 200 mg DIDP/kg diet, corresponding with 18.4 mg/kg b.w/day. Since CAT is considered to be not specific for peroxisome proliferation this latter value has been established as overall no-observed-effect-level.

In a study in which male rats have been exposed to 0, 200, 600, 2000, 6000 and 20000 mg benzylbutylphthalate (BBP)/kg diet for 2 weeks, body weight and liver weight and a number of enzyme parameters which are related with peroxisome proliferation (palmitoyl coenzyme-A oxidase (PCO), enoyl coenzyme-A hydratase (ECH), carnitine acetyl transferase (CAT) and lauric acid hydroxylase (LAH)) have been determined in liver homogenates. No effect has been observed on the liver weight. The body weight showed a significant decrease as the highest dose level. PCO and CAT showed no effect up to 600 mg BBP/kg diet. LAH was more sensitive with a dose-without-effect (DWE) of 200 mg BBP/kg diet, corresponding with 19.1 mg BBP/kg b.w./day. ECH appeared to be the most sensitive parameter with an effect in all dose levels used. Therefore, no overall no-observed effect level can be defined in this experiment.

In a study in which male rats have been exposed to 0, 200, 600, 2000, 6000 and 20000 mg diethylphthalate (DEP)/kg diet for 2 weeks, body weight and liver weight and a number of enzyme parameters which are related with peroxisome proliferation (palmitoyl coenzyme-A oxidase (PCO), enoyl coenzyme-A hydratase (ECH), carnitine acetyl transferase (CAT) and lauric acid hydroxylase (LAH) have been determined in liver homogenates. No effects have been observed on the liver and body weights. PCO and LAH showed no effects up to 2000 and 600 mg DEP/kg diet, respectively. ECH was more sensitive with a dose-without-effect (DWE) of 200 mg/kg diet. Cat was the most sensitive parameter with an effect in all dose groups. Although CAT turned out the most sensitive parameter, this enzyme was not considered in the establishment of an overall no-observed-effect-level for peroxisome proliferation since it is not specific for peroxisome proliferation. The second most sensitive parameter was the ECH activity. Therefore an overall no-observed-effect-level for peroxisome proliferation of 200 mg DEP/kg diet was established corresponding to 19 mg DEP/kg b.w./day.

In a study in which male rats have been exposed to 0, 20, 60, 200, 600 and 2000 mg di(cyclohexyl)phthalate (DCHP)/kg diet for 2 weeks, body weight and liver weight and a number of enzym parameters which are related with peroxisome proliferation palmitoyl coenzyme-A oxidase (PCO), enoyl coenzyme-A hydratase (ECH), carnitine acetyl transferase (CAT) and lauric acid hydroxylase (LAH) have been determined in liver homogenates. No effects have been observed on the liver and body weights. CAT showed no effect up to 600 mg DCHP/kg diet. PCO and LAH were more sensitive with a dose-without-effect (DWE) of 200 mg DCHP/kg diet. ECH, an enzyme involved in the beta-oxidation, appeared to be the most sensitive parameter with a dose-without-effect of 60 mg DCHP/kg diet. Therefore an overall no-observed-effect-level of 60 mg DCHP/kg diet was defined corresponding to 5.8 mg DCHP/kg b.w./day.