Residue surface

By using an effective, distance-dependent dielectric constant, the ability of bulk water to reduce electrostatic interactions can be mimicked without the presence of explicit solvent molecules. One disadvantage of aU vacuum simulations, corrected for shielding effects or not, is the fact that they cannot account for the ability of water molecules to form hydrogen bonds with charged and polar surface residues of a protein. As a result, adjacent polar side chains interact with each other and not with the solvent, thus introducing additional errors. 

When fouling occurs, even mechanical cleaning does not remove all traces of the bio film. Previously fouled and cleaned surfaces are more rapidly colonized than new surfaces. Residual biofilm materials promote colonization and reduce the lag time before significant fouling reappears. 

Raju J, Gupta VK. 1989. A new extractive spectrophotometric method using malonyl dihydrazide for the determination of organophosphoms pesticides in surface residues. Microchem J 39 166-171. 

NDO can be classified as class III dioxygenase the electron transfer chain involves a Rieske-type ferredoxin. Electrons enter NDO through the Rieske-type cluster of the dioxygenase. Kauppi et al. (11) have suggested that the binding site of NDO for the ferredoxin involves the 6 strands 10 and 12 of the Rieske domain as well as residues from the catalytic domain that form a depression in the protein surface close to Cys 101, which is a ligand of the Rieske cluster. In Rieske proteins from be complexes, access to this side of the cluster is blocked by an acidic surface residue (Asp 152 in the ISF, Glu 120 in RFS). 

Surface residues must not be removed during sampling. 

Whatever the case, the ability to irrigate test plots is an important consideration during field site selection. Sprinkler irrigation is preferred. Flood and furrow irrigation should be avoided since they may disturb surface residues, resulting in uneven residue distribution and/or inadvertent agrochemical loss from the study plots. Recommended irrigation practices are discussed in more detail in Section 3.3.8. 

Outer retainer sleeve (A) remains in soil to prevent drag down of surface residues to lower soil profile... 

Empirical evidence supporting the role of soil micro-layer losses in zero-time issues is given by the often-seen rise in post zero-time residue recoveries. The improved recoveries likely result from the micro-layer residue redistribution that reduces losses of the highly concentrated surface residues. There has been some speculation that zerotime core recoveries may be due to volatilization losses not measured by standard laboratory studies. If this were the case, however, increases in residue concentrations would not occur over time since volatilized residues would be lost to the atmosphere. ... 

Apply the supplemental water inputs via sprinkler irrigation. Do not flood or furrow irrigate since these practices may disturb soil surface residues. Be aware that even... 

Dislodgeable soil residue (DSR) studies are used to determine exposure of re-entry workers to soil surface residues. Soil surface residues are defined as test substance residue levels in <150-q.m soil particles (i.e. soil dust which can stick to a worker s skin, or can be inhaled). 

Surface residues of DDT and parathion at various times during the season and at harvest were determined for apples, pears, peaches, oranges, and lemons. Low level surface residues of parathion on apples were not carried over into cider. Harvest residues on fresh fruit are distinguished from residues present in food at the time of consumption which are included under the designation ultimate residues. 

BARNES et o/.—FRUIT SURFACE RESIDUES OF DDT AND PARATHION AT HARVEST... 

Table I. Surface Residues of DDT on Rome Beauty Apples at Harvest...

Surface residues of DDT on apples resulting from experimental applications applied in schedules comparable to commercial usage ranged from less than 0.5 to 2.0 p.p.m. at harvest. Schedules of application involving higher spray concentrations and greater frequency of application than are at present required in commercial practice resulted in most cases in residues of less than 7 p.p.m. Typical harvest residues are presented in Table I. 

On pears, experimental applications of DDT applied in commercial schedules resulted in surface residues ranging from less than 0.5 to approximately 3 p.p.m. Typical harvest residues are shown in Table II. 

Intervals between application and sampling of apples retaining weathered surface residues of parathion ranged between 21 and 70 days. At harvest, these residues were 0.05 p.p.m. or less, following each of 13 varied schedules of application (Table III). (These values are derived from samples containing an optimum amount of parathion for analytical precision.) Low level surface residues on apples were not carried over as ultimate residues in cider (Table III). This fact supports the contention that there is close association of the parathion deposits with the waxlike coating of the fruit. 

Surface residues of parathion on peaches were 4- to 15-fold higher than for comparable schedules on apples or pears, possibly because of the higher initial deposits retained on the more retentive surfaces of these fruits. Surface residues of DDT on peaches were also higher than those which would be expected to result from comparable schedules on apples and pears. Typical residue values for peaches are shown in Table V. 

As compared with the residues of DDT present within citrus peel (2), the relative significance of surface residues of DDT on citrus fruits is diminished by the fact that these are readily removed in large proportion by the usual packinghouse processing (5). 

Table IV. Surface Residues of Parathion on Bartlett Pears...

Table VI. Attenuation of Posttreatment Surface Residues of DDT on Citrus Following...

On lemons, surface residues at harvest ranged from 2 to 3 p.p.m. (Table VIII), somewhat larger amounts being generally present within the peel (2). 

Table VIII. Attenuation of Surface Residues of DDT on Eureka Lemons...

Studies on oranges (Table IX) have shown that surface residues of parathion are also of relatively low magnitude in comparison with the quantities found within the peel ( ). Surface residues on these fruits decreased rapidly (5), reaching values of 0.01 p.p.m. or less at harvest following a single application at required dosages. 

Standardized procedures were adopted with regard to sample preparation, recovery of toxicant, and chemical assay. In order to determine the nature and magnitude of penetrated residues, it was necessary to disassociate all extra-surface residues. The techniques originally developed to effect this separation and which were used in most of the DDT penetration studies have been described by Gunther 11). Certain modifications which have been developed subsequently in connection with the parathion studies are described in detail below since this phase of penetration studies assumes singular importance (see also 14). 

---