Texas Animal Health Commission

We investigated the effect of different densities (0, 20, or 40) of developing larval Aedes triseriatus (Say) on bacterial abundance, bacterial productivity, and leaf fungal biomass in a microcosm experiment. Larvae in the low-density treatment developed normally, but larvae at the high density were significantly slower to develop. Both bacterial abundance (direct microscopic counts) and bacterial productivity (3H-leucine incorporation rates) on leaf material were significantly lower in the presence of larvae. Bacterial abundance in the water column did not change significantly with treatment, but bacterial productivity varied with time and declined significantly at both larval densities. Bacteria on the walls and bottom of the containers also were less abundant and significantly less productive in the presence of larvae. Aside from presence/absence effects, there was no clear evidence that larval impacts were density-dependent. Leaf-associated fungal biomass, as measured by ergosterol levels, varied with time but was not significantly affected by any treatment, suggesting most fungal tissue was incorporated in the leaf matrix and unavailable to larvae. Based upon estimated biomass accrual and respiration of larvae, it appears that bacterial biomass and production were insufficient to account for carbon demands of growing larvae. Because fungal biomass and leaf mass likely contributed little to gross larval demands, other carbon sources (e.g., protozoa and extracellular microbial components) were probably used by larvae. Although apparently insufficient for all larval carbon demands, bacterial and leaf fungal biomass may be adequate for other larval nutritional needs (i.e., nitrogen and essential lipids).

A mathematical model was developed to simulate the transport and dissolution of colloidal particles with a water‐soluble component in a porous medium. The model is based on mass balance equations describing the mass transport, dissolution, sorption, capture, and release of colloids in a three‐phase medium consisting of a solid matrix, an aqueous phase, and colloids. Colloid dissolution, contaminant sorption on solid matrix, and colloid capture mechanisms are represented by first‐order kinetics. A numerical comparison of the model of a water‐soluble component associated with fly ash–mobilized transport and transport due only to dissolved component migration indicates that the presence of colloids significantly increases the aqueous phase contaminant concentration.

To evaluate differences in milk production between cows with positive and negative caudal fold tuberculin test results in a Mycobacterium bovis-infected dairy herd. Cross-sectional epidemiologic survey. 369 Holstein cows with lactation duration between 200 and 360 days. The caudal fold tuberculin test was performed. Information on milk production data, parity, calving season, days of lactation, previous milk production, and whether cows had clinical mastitis was obtained from farm records. Composite milk samples were collected and submitted for bacterial culture. 170 cows had positive tuberculin test results, and 199 had negative results. Cows with positive test results produced less milk (mean, 347 kg [763 lb]) than did cows with negative test results after adjusting for variables biologically related to milk production. Calving season (spring, summer) was significantly associated with reduced milk production. Cows with clinical mastitis produced less milk than did cows without clinical mastitis, but the difference was not statistically significant in the multiple regression analysis. In this herd, tuberculosis was associated with a 4% decrease in milk production. Milk production losses per cow attributable to calving season (spring, summer) were 3 times those attributable to tuberculosis. However, because of the high prevalence of tuberculosis in this herd, the impact of tuberculosis on total herd milk production was an additional cause for concern.

To evaluate differences in prevalence of tuberculosis (TB) in adult beef cattle that originated from different states in Mexico and were shipped direct-to-slaughter into Texas in 1995. Epidemiologic survey. Approximately 65,000 adult beef cattle. Postmortem examinations of carcasses for detection of Mycobacterium bovis infection were conducted at slaughter plants in Texas. Specimens were collected from cattle with granulomatous lesions, stored in neutral-buffered 10% formalin or saturated sodium borate solution, and processed for histologic and bacteriologic diagnosis. Prevalence and 95% confidence intervals were estimated by state of origin. Difference between prevalences for different states was tested for significance (P < 0.05), using the proportion test. Overall prevalence of TB at slaughter in adult beef cattle that originated from Mexico was approximately 0.5/1,000 (34/65,233). Prevalence of TB in cattle that originated from Chihuahua (0.07) was significantly lower than that in cattle from Coahuila (0.80), Nuevo Leon (1.27), and Tamaulipas (1.81). Prevalence of M bovis infection in adult beef cattle may be significantly different between states in the northern border region of Mexico. On the basis of disease prevalence and numbers of exported cattle and provided safeguards such as TB testing are continued, cattle from Chihuahua may pose a lower risk of TB transmission to Texas cattle than do cattle from Coahuila, Nuevo Leon, and Tamaulipas. To allow interstate/international movement of cattle from northern border states of Mexico, TB testing requirements should be continued. In the context of international trade, southern border states of the United States should continue collaborating with northern border states of Mexico to control and eradicate this disease.

Macrobenthic communities were surveyed in 1987–88 as part of acomprehensive study of fish kills and water quality in the upper TrinityRiver. The purpose was to characterize macrobenthic integrity in relation toambient and storm-associated water quality and other environmental factors.No physical habitat features were found to be substantially limiting toaquatic life. Water and sediment quality generally were good, andmacrobenthic communities typically were healthy. Ecological conditions werevastly improved compared to the recent past, attributable mainly todecreased contaminant loading from wastewater treatment plants and reducedincidence of raw sewage bypassing. Nonetheless, some impact was evident incertain reaches. Deleterious effects at Beach St. evidently resulted frompesticides derived from urban runoff. Slight impacts by dissolved metalswere suggested for Grand Prairie and Continental Ave.; possible sourcesincluded urban runoff and wastewater treatment plant effluents. Moderateimpacts at S. Loop 12 were attributed to low-flow toxicity induced by awastewater treatment plant discharge; ammonia and chlorine were consideredprimarily responsible, with metals and pesticides possibly involved.Macrobenthic communities were somewhat degraded from Trinidad to US 79, dueto storm-related stresses by DO depression, pesticides, and metallic oxides.Overall impacts were relatively slight on a long-term basis, however, and ahigh aquatic life use was attained at most sites. The degree of macrobenthicintegrity was considered remarkable for an effluent-dominated system withsuch extensive urbanization in the watershed.

A goal of our research is to identify biochemical factors that underlie the susceptibility of bone marrow cell populations to benzene metabolites so as to develop a mechanistically based chemoprotective strategy that may be used in susceptible humans exposed to benzene.By doing biochemical risk analysis of bone marrow stromal cells from mice and rats and the human myeloid cell lines, HL-60 and ML-1; and by using buthionine sulfoximine and dicumarol we have observed that the susceptibility of these cell populations to hydroquinone (HQ) correlates with their concentration of glutathione (GSH) and activity of quinone reductase (QR).Accordingly, the induction of QR and GSH by 1,2-dithiole-3-thione (D3T) in these cell populations has resulted in a significant protection against the following hydroquinone-mediated toxicities: inhibition of cell proliferation and viability; reduced ability of stromal cells to support myelopoiesis; and altered differentiation of ML-1 cells to monocytes/macrophages.Preliminary in vivo experiments indicate that feeding mice D3T results in an induction of QR in the bone marrow compartment such that stromal cells are more resistant to hydroquinone-induced cytotoxicity in vitro.Overall, these studies suggest that in addition to hepatic cytochrome P4502E1, bone marrow OR and GSH are factors that could determine an individual's relative susceptibility to the toxic effects of benzene.

Routine use of solid-phase sediment toxicity tests for scientific and regulatory purposes necessitates the development of solid-phase reference toxicant materials. In order to evaluate an approach for developing such materials, 12 solid-phase 96-h reference toxicant tests were conducted over 12 weeks with the marine bivalve Mulinia lateralis. Reference toxicant material was clean muffled sand spiked with copper used in a conventional dilution series with unspiked sand as the diluent. Control survival ranged from 92 to 100% and during the exposure weights increased by a factor of about 3 relative to initial weights. Measured concentrations of copper in the water column above the reference material during testing showed that the toxicant exposures were relatively consistent between tests. Coefficients of variation (CV) for mortality and sublethality (growth) endpoints were 39% and 42%, respectively. Coefficients of variation for other solid-phase reference toxicant material studies do not exist, but comparison of the results of this study with water-only literature values are favorable. Values for CVs in the literature range from 4 to 120% and 2 to 48% for acute and sublethal endpoints, respectively, for water column organisms and about 45% for an acute test using the marine amphipod (Ampelisca abdita). This evaluation demonstrates that use of sand spiked with copper is a credible approach for developing a solid phase reference toxicant material; however, further development is required to reduce both biological and chemical sources of variability.