Underlying issues including approaches and information needs in risk assessment.

Risk assessment requires a delicate consideration of the factors modifying exposure and effects. In this contribution a review is given of the qualitative and quantitative information needs that are essential for a proper risk assessment. The focus is on the details of metal exposure and exposure assessment, following the themes of environmental, physicochemical, and biological components that define exposure. Apart from a description of the principle processes and pathways, exposure assessment is placed in the context of risk assessment and its use in policy and regulatory decision making.

Ela 1.0--a framework for life-cycle impact assessment developed by the Fraunhofer-Gesellschaft. Part A: The conceptual framework.

The Fraunhofer-Gesellschaft has sponsored the development of a conceptual and flexible, computer aided tool to perform the impact assessment within LCA (life cycle assessment) for technical products and processes. The developed general framework "Ela 1.0" (environmental loads analysis) consists of four elements: the selection of appropriate impact categories, the categorization of emissions and wastes leaving the systems as well as of resource and energy consumption, the characterization and an analysis of the results of the impact assessment. The latter compares the product-based emissions with the total of emissions of a region such as Germany, the EU or OECD countries. The framework Ela 1.0 considers the environmental categories: global warming, ozone depletion, resource and energy consumption, wastes, eutrophication (including COD and BOD as measured parameters), acidification, ecotoxicity, ozone formation and human toxicity. The latter categories are handled by listing of precursors for ozone formation, and by listing of emissions scored according to their human hazard potential. The options, possibilities and limitations of the conceptual framework are presented in part A of a series of publications.

Assessment of the environmental behaviour of antioxidants in folios. Comparative risk analysis for the use of folios in agriculture.

The objective of the reported study has been to assess and evaluate as comprehensively as possible the environmental impact of Octadecyl 3(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (CAS no: 2082-79-3, Irganox 1076, Ciba Specialty Chemicals Inc., Additives), which is used as an antioxidant. The potential impact on the compartments soil, groundwater and surface water is to be considered. For comparative purposes, additionally, other chemical compounds being currently under environmental discussion are also taken into account. These comprise pesticides and phthalates which are ubiquitously distributed plasticizers as well as a complexing agent. Since the data basis for each of the compounds under consideration is different, a tiered approach comprising various methodologies of impact assessment has been chosen to achieve the best possible comprehensiveness. The tiers are: 1. Tier: hazard assessment using a scoring system 2. Tier: comparative risk assessment. When interpreting the results of each method, system boundaries as well as underlying assumptions were taken into consideration. Both methodologies showed, that-as compared to the reference substances-there is no relevant environmental and toxicological concern due to low environmental and human hazard from Octadecyl 3(3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

Purification and mechanistic properties of an extracellular alpha-L-arabinofuranosidase from Monilinia fructigena.

1. The alpha-L-arabinofuranosidase isoenzyme designated AFIII [Laborda, Archer, Fielding & Byrde (1974) J. Gen. Microbiol. 81, 151-163] was purified by sequential isoelectric focusing, hydrophobic chromatography, gel filtration and chromatofocusing. 2. The enzyme is a monomer of Mr 40,000. 3. On inactivation of the enzyme with 3H-labelled 1-alpha-L-arabinofuranosylmethyl-3-p-nitrophenyltriazene, 0.64 mol of alpha-L-arabinofuranosylmethyl residues/mol of enzyme is estimated to become attached to protein. 5. Neither first-order nor second-order rate constants for hydrolyses of aryl alpha-L-arabinofuranosides are dependent upon leaving-group acidity [beta lg(V) = -0.16 +/- 0.11; Beta lg(V/K) = -0.11 +/- 0.07; n = 7; delta pKa = 4.5] 6. Bond-breaking is nonetheless rate-limiting, as is shown by a value of 18(V) of 1.030 +/- 0.007 for the hydrolysis of p-nitrophenyl arabinoside. 7. Proton-donation to the leaving group is thus far advanced at the rate-limiting transition state for this enzyme. 8. Four alpha-L-arabinofuranosyl pyridinium salts are substrates, and an approximate beta lg(V) value of -0.9 can be estimated. 9. The absolute rate enhancement with the 4-bromoisoquinolinium salt, 2.5 X 10(9), is comparable with that observed with pyranosidases. 10. Ring-opening mechanisms can therefore be dismissed, even though they are known in the acid-catalysed hydrolysis of arabinofuranosides.

Goat liver beta-mannosidases: molecular properties, inhibition and inactivation of the lysosomal and nonlysosomal forms.

The two caprine hepatic beta-mannosidases have been partially purified and their properties have been compared. The lysosomal beta-mannosidase A had an apparent molecular weight of 127,000 +/- 10,000 and an isoelectric point of pH 6-7. Its activity was unaffected by incubation with Triton X-100 (0.1%) and cysteine (20 mM) and it hydrolyzed the presumed natural substrates, Man(beta 1-4)GlcNAc and Man(beta 1-4)GlcNAc(beta 1-4)GlcNAc. The nonlysosomal beta-mannosidase B had an apparent molecular weight of 43,000 +/- 2,000 and an isoelectric point of pH 5.5. beta-Mannosidase B was activated by Triton X-100 (0.1%) and was inhibited by cysteine (20 mM). Hydrolysis of Man(beta 1-4)GlcNAc, but not of Man(beta 1-4)GlcNAc(beta 1-4)GlcNAc, followed incubation with beta-mannosidase B. 1,5-Dideoxy-1,5-imino-D-mannitol did not inhibit the A enzyme and only feebly (Ki = 0.3 mM) inhibited the B enzyme; beta-D-mannopyranosylmethyl p-nitrophenyl triazene did not inactivate either enzyme but 1,2-anhydro-1,2,3,5,6/4-cyclohexane hexol inactivated the B enzyme only. The radical mechanistic differences between the two enzymes argue against their having the same genetic origin.

Identification of an essential carboxylate group at the active site of lacZ beta-galactosidase from Escherichia coli.

[3H] Conduritol C cis-epoxide (1,2-anhydro-epi-inositol, I) was synthesized as an active-site-directed inhibitor for lacZ beta-galactosidase from Escherichia coli. A considerable kinetic isotope effect was noted in the reduction by [3H]NaBH4 of the p-benzoquinone-derived precursor for I. Complete loss of beta-galactosidase activity occurred on incorporation of 4 mol I/mol beta-galactosidase tetramer. The inhibitor was very labile in the denatured enzyme at pH greater than 8, implying the formation of an ester bond between I and a carboxylate at the active site. The radioactive material released from the labeled enzyme was identified as allo-inositol. The stereochemistry of the expoxide reaction (trans-diaxial ring opening) is thus the same as for beta-glucosidases with the corresponding epoxides. The binding site for I was identified as Glu-461 by the isolation and partial sequence analysis of a radioactive octapeptide from the cyanogen bromide and pepsin fragments of the labeled enzyme. A failure to determine the N-terminal amino acid of the labeled peptide is ascribed to the great reactivity of the esterified gamma-carboxyl group of its N-terminal Glu-461 which causes rapid cyclisation of this residue to pyroglutamate, even under weakly basic conditions. The participation of the carboxylate of Glu-461 in catalysis is discussed.