PubMed · 11432703
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R E Clement, P W Yang. 2001-06-15. Environmental analysis.. https://doi.org/10.1021/ac0103930
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Three field experiments were performed to assess the clearance, uptake, and exchange kinetics of polychlorinated biphenyls (PCBs) between grass and the atmosphere using mixed- and single-species grass (Holcus lanatus). In the clearance experiment, the grass was artificially contaminated by equilibration with diluted Aroclor vapor then exposed to field air, and the rates of depletion were monitored by sampling at regular intervals to determine clearance rate constants. In the uptake experiment, the uptake of PCBs from the ambient atmosphere was followed in growing grass at ambient concentrations for 3 and 6 weeks by analysis of segmented samples along the length of the sward. In the third experiment, diurnal temperature-driven changes in grass concentrations were measured. The results indicate that the grass is behaving as a two-compartment system: (1) a fast-exchanging surface adsorption site with a response time of hours and a capacity essentially independent of K(OA), the octanol-air partition coefficient and (2) a slow responding site with a response time of weeks, the capacity of which is related to K(OA). The kinetic and equilibrium phenomena involved in grass-air exchange are thus complex and are not adequately described by simple first-order rate constants and equilibrium partitioning coefficients.
A multiclass/multiresidue method for surveying the uptake of plant protecting chemicals by inhalation during field spraying work is described. Eleven nowadays mainly dispersed compounds, which cover a wide range of chemical properties, are analysed in air with personal active sampling and in one single analytical run. This has the advantage, that one basic method only needs to be implemented, calibrated and validated in a laboratory to perform varying monitoring tasks without changing the method itself. Samples were taken with Tenax sorbent tubes operated to collect the active compounds simultaneously in the vapour state, in aerosol state or bound to particles. The procedure consists of four unit operations only: sampling, elution, dilution and HPLC measurement, and is described in SOP-format. The limits of quantification, calculated as method detection limits, were between 1 and 9 microg m(-3) based on 1 m3 air volume sampled (8 h). Method performance was characterised by way of generated test atmospheres and field spraying trials.
Phosphoglycolate phosphatase (PGPase), a key enzyme of photorespiration in photosynthetic organisms, was purified from Chlamydomonas reinhardtii. The enzyme was an approximately 65-kDa homodimer with a pI value of 5.1 composed of approximately 32-kDa subunits not connected by any S-S bridges. It was also highly specific for phosphoglycolate with a K(m) value of 140 microm and an optimal pH between 8 and 9. The activity was strongly inhibited by CaCl(2), and it recovered competitively following the addition of MgCl(2) or EGTA. A mobility shift was observed in SDS-polyacrylamide gel electrophoresis by the addition of CaCl(2), indicating that the enzyme binds to Ca(2+). The N-terminal region of amino acid sequence deduced from cDNA sequence that was not contained in the purified PGPase had similar characteristics to those of typical stroma-targeting transit peptides in C. reinhardtii. The following region of the deduced sequence containing 302 amino acid residues was similar to p-nitrophenylphosphatase-like proteins, although the purified PGPase did not hydrolyze p-nitrophenylphosphate. Genomic DNA fragments from wild type containing the sequence homologous to the cDNA for PGPase complemented the PGPase-deficient mutant pgp1. Possible regulatory mechanisms during adaptation to limiting CO(2) were discussed based on the characteristics of the purified PGPase and the deduced amino acid sequence.