Partitioning of monomethylmercury between freshwater algae and water.

Phytoplankton-water monomethylmercury (MeHg) partition constants (KpI) have been determined in the laboratory for two green algae Selenastrum capricornutum and Cosmarium botrytis, the blue-green algae Schizothrix calcicola, and the diatom Thallasiosira spp., algal species that are commonly found in natural surface waters. Two methods were used to determine KpI, the Freundlich isotherm method and the flow-through/dialysis bag method. Both methods yielded KpI values of about 10(6.6) for S. capricornutum and were not significantly different. The KpI for the four algae studied were similar except for Schizothrix, which was significantly lower than S. capricornutum. The KpI for MeHg and S. capricornutum (exponential growth) was not significantly different in systems with predominantly MeHgOH or MeHgCl species. This is consistent with other studies that show metal speciation controls uptake kinetics, but the reactivity with intracellular components controls steady-state concentrations. Partitioning constants determined with exponential and stationary phase S. capricornutum cells at the same conditions were not significantly different, while the partitioning constant for exponential phase, phosphorus-limited cells was significantly lower, suggesting that P-limitation alters the ecophysiology of S. capricornutum sufficiently to impact partitioning, which may then ultimately affect mercury levels in higher trophic species.

Pesticides in canals of South Florida.

Atrazine, ametryn, bromacil, simazine and norflurazon were the most frequently detected pesticides in surface water samples and DDE, DDD and ametryn were the most frequently detected pesticides in sediment samples collected over the period November 1991 to June 1995 in a monitoring network that includes 27 stations in south Florida canals. The 744 pesticide detections during this time period represent about 2% of the total number of analytical determinations. Many of the most frequently detected compounds were used in large amounts in the monitoring area based on pesticide usage estimates included in this study. Spatial trends in pesticide detections followed use patterns. The maximum atrazine detections occurred in winter to late spring and were associated with usage on turfgrass and agricultural products. Endosulfan residues above the Florida water quality criterion were occasionally observed in surface water in the Homestead area and most of the exceedences occurred in confined waters. Methods with lower MDLs have recently been developed and should increase the number of detections in future sampling. Pesticides which bind strongly to soil, pesticides that are highly persistent and those used in large amounts were some of the more frequently found pesticides in sediments.

Determination of ethylenethiourea in crops using particle beam liquid chromatography/mass spectrometry.

Several food crops were analyzed for residues of ethylenethiourea (ETU), a suspect thyroid and liver carcinogen present in EBDC fungicides, using a commercial particle beam (PB) LC/MS method. The PB/LC/MS detection limits for ETU in crops (5 ppb, 1.25 ng) are comparable to those obtained by LC with electrochemical detection. Spectra obtained from crop samples containing as little as 5 ng of ETU were matched with the NBS library reference EI spectrum. Isotopically labeled ETU was used as an internal standard for quantitation and determination of recoveries. No enhancement of molecular ion signal intensity from unlabeled ETU was observed upon coelution with the isotopically labeled variant. This MS method permits detection of ETU with increased selectivity without compromising sensitivity.

Determination of oxyfluorfen herbicide and oxyfluorfen amine residues in garbanzo beans by liquid chromatography.

Oxyfluorfen and oxyfluorfen amine were determined by liquid chromatography (LC) with ultraviolet (UV) and photoconductivity detection (PCD). A simple extraction procedure acceptably recovered both analytes from garbanzo beans over a wide range of fortifications (0.05 to 20 ppm) (83 +/- 4 for oxyfluorfen; 85 +/- 4 for oxyfluorfen amine). Percent recoveries decreased slightly as the fortification level decreased. Both analytes could be determined simultaneously at a concentration greater than 0.2 ppm in garbanzo beans. Detection limits were 3 ng for oxyfluorfen and 100 ng for oxyfluorfen amine using LC/UV, and 12 ng for both oxyfluorfen and oxyfluorfen amine with LC/PCD. Different knitted reaction coils and photoreactors were evaluated. Photoproduct yields and identification were determined by ion chromatography. The LC/PCD method measures oxyfluorfen and oxyfluorfen amine separately and has a shorter analysis time, while the standard method using gas chromatography measures total residues and is more sensitive.

Determination of nabam fungicide in crops by liquid chromatography with postcolumn reaction detection.

The ethylenebisdithiocarbamate (EBDC) fungicide, nabam, was determined in several crop matrixes using liquid chromatography with postcolumn reaction detection. After separation by micellar liquid chromatography, nabam (EBDC sodium salt) was acid hydrolyzed to ethylenediamine and fluorigenically labeled with o-phthalaldehyde-mercaptoethanol (OPA-MERC). Standard curves were linear from the detection limit of ca 1 ng to 1000 ng. Nabam was recovered in high yield (89 plus or minus 7.7%) over a range of concentrations (0.1 to 20 ppm) from fortified samples of papaya, lettuce, cucumber, spinach, and applesauce using a simple extraction method. Efforts to convert the more popular EBDC fungicides, maneb and mancozeb, to nabam are discussed.

The pharmacoeconomics of renal transplantation: increased drug costs with decreased hospitalization costs.

We evaluated the economic and clinical effects of two immunosuppressive drug regimens used to treat recipients of human leukocyte antigen (HLA)-identical sibling donor renal transplants during the first posttransplant year. We compared consecutive patients in two groups of 30 who were given either antilymphoblast globulin (ALG), azathioprine, plus prednisone or cyclosporine, azathioprine, and prednisone for immunosuppression. We standardized all dollar values, costs and charges, to the 1986 level using our hospital's health care charge inflation rate. There were no significant differences between the two treatment groups for actual patient (100% vs 93%; p = 0.51) and graft survival rates (100% vs 93%; p = 0.51), average serum creatinine level (1.0 +/- 0.3 vs 1.0 +/- 0.2 mg%; p = 0.46), and most recent creatinine level (1.4 +/- 0.3 vs 1.4 +/- 0.7 mg%; p = 0.45). The average cyclosporine-azathioprine-prednisone costs were $3987/patient more for the first year of therapy than for ALG-azathioprine-prednisone. However, the former regimen produced an average of $9543/patient less in total hospitalization charges. This was due to both a shorter initial hospital stay and a decreased rate of rehospitalization, with a lower frequency of acute rejection episodes (p = 0.001) and infectious complications (p = 0.05). We conclude that, although this cyclosporine-containing protocol was associated with increased drug costs, it is justified by decreased hospitalization charges that resulted from improved efficacy and safety.

A rapid gas chromatographic procedure for the analysis of oxalate ion in urine.

A specific, precise, rapid and sensitive method for the analysis of oxalic acid in urine is described. This microanalytical procedure can detect concentrations of urinary oxalic acid as low as 4 mg/l with a relative standard deviation of replicates of less than 5% (24-h urine collections). 10% BCl3:2-chloroethanol is used to derivatize 0.1 ml of urine after evaporation to dryness or lyophilization. The bis-2-chloroethyl ester of oxalic acid formed is extracted into ethyl acetate/isopropyl ether (1:3, v/v) and is detected by electron capture gas chromatography at the 50 pg level. The total analysis time for 35 samples in 8 h per GC column. A series of determinations of urinary oxalic acid in 21 kidney stone-forming patients resulted in values ranging from 10.6 to 42.0 mg/24 h with a mean recovery of added oxalic acid of 98.2% (range 84.0-111.3%).