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  • Author: S.J. Harris, x
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National governments introduced residue limits and guideline levels for pesticide residues in water when policies were implemented to minimize the contamination of ground and surface waters. Initially, the main attention was given to drinking water.

Regulatory limits for pesticide residues in waters should have the following characteristics: definition of the type of water, definition of the residue, a suitable analytical method for the residues, and explanation for the basis for each limit.

Limits may be derived by applying a safety factor to a no-effect-level, or from levels occurring when good practices are followed and also passing a safety assessment, or from the detection limit of an analytical method, or directly by legislative decision.

The basis for limits and guideline values issued by WHO, Australia, the United States, New Zealand, Japan, Canada, European Union, and Taiwan is described, and examples of the limits are provided. Limits have been most commonly developed for drinking water, but values have also been proposed for environmental waters, effluent waters, irrigation waters, and livestock drinking waters. The contamination of ground water is of concern because it may be used as drinking water and act as a source of contamination for surface waters. Most commonly, drinking water standards have been applied to ground water.

The same terminology may have different meanings in different systems. For example, guideline value (GV) in WHO means a value calculated from a toxicology parameter, whereas in Australia, a GV is at or about the analytical limit of determination or a maximum level that might occur if good practices are followed. In New Zealand, the GV is the concentration where aesthetic significance is influenced.The Australian health value (HV) is conceptually the same as the WHO GV. The New Zealand maximum acceptable value (MAV) and the Canadian maximum acceptable concentration (MAC) are also conceptually the same as the WHO GV.

Each of the possible ways of defining the residues has its merits. A residue limit in water expressed as the sum of parent and toxicologically relevant transformation products makes sense where it is derived from the acceptable daily intake (ADI). For monitoring purposes, where it is best to keep the residue definition as simple as possible for the sake of practical enforcement and economy, theparent or a marker residue is preferable. It is also possible for parent and degradation products (hydrolysis and photolysis products and metabolites) to become physically separated as the water moves through soil strata, which suggests that separate limits should be set for parent and important degradation products.

The Commission has made 12 recommendations for regulatory limits for pesticide residues in water. The recommendations will act as a checklist for authorities introducing or revising limits or guidelines for pesticide residues in water.

Abstract

Atomistic simulations using lattice and molecular dynamics were carried out on the {210}, {310}, and {410} tilt grain boundaries of MgO as a function of pressure up to 100 GPa at a single temperature of 600 K. The calculations show a significant change in the structure of the tilt grain boundaries as pressure increases. The results show that, beyond the previously identified reversible pressure induced collapse of the channel structure, an irreversible shear was identified that forms a mirror grain boundary, which does not possess well-defined dislocation cores and is consequently denser. These mirror boundaries are energetically more favorable than the symmetric boundaries at elevated pressures. As applied pressure approaches 100 GPa a reversible structural transition occurs causing the boundaries to shear perpendicular to the boundary plane forming highly dense structures that contained seven coordinate ions at the boundary and the presence of an edge dislocation-like structure. We suggest that differences between the boundary structures seen in the HREM studies with those predicted by simulations may result from stresses upon the crystal during preparation causing irreversible shearing.

The Lectures of 1827

Abstract

Meprins are zinc-endopeptidases of the astacin family, which are expressed as membrane-bound or secreted forms in renal and intestinal brush-border membranes of mouse, rat and man. There are two types of meprin subunits, α and β, which form disulfide-bonded homo- and heterodimers; further oligomerization is mediated by non-covalent interactions. Both subunits are translated as proenzymes that have to be activated by removal of an N-terminal propeptide. In the gut, the most probable activator is trypsin. In addition, plasmin has been shown to activate the human α subunit in colorectal cancer tissue. In the present study we have overexpressed the human meprin α subunit and a His-tagged soluble tail-switchmutant of meprin β in Baculovirus-infected insect cells. The recombinant homo-oligomeric proteins were purified by gel filtration and affinity chromatography with yields of up to 10 mg/l cell culture medium and analyzed with regard to their activation mechanism. While both α and β homo-oligomers are activated by trypsin, only meprin α homo-oligomers are processed to their mature form by plasmin. These results indicate a different accessibility of the propeptide in meprin homo-oligomers and suggest an explanation for the appearance of meprin hetero-oligomers consisting of active α, but latent β subunits.

Abstract

The availability and use of online counseling approaches has increased rapidly over the last decade. While research has suggested a range of potential affordances and limitations of online counseling modalities, very few studies have offered detailed examinations of how counselors and clients manage asynchronous e-mail counseling exchanges. In this paper we examine e-mail exchanges involving clients and counselors through Kids Helpline, a national Australian counseling service that offers free online, e-mail, and telephone counseling for young people up to the age of 25. We employ tools from the traditions of ethnomethodology and conversation analysis to analyze the ways in which counselors from Kids Helpline request that their clients call them, and hence change the modality of their counseling relationship, from e- mail to telephone counseling. This paper shows the counselors' three multilayered approaches in these e-mails as they negotiate the potentially delicate task of requesting and persuading a client to change the trajectory of their counseling relationship from text to talk without placing that relationship in jeopardy.