Confounding factors toxicity

A cohort mortality study was conducted to compare the mortality rates due to chronic renal disease in 4,519 battery plant workers and 2,300 lead production or smelter workers from 1947 to 1980 (Cooper 1988 Cooper et al. 1985). The mortality data for these workers were compared with national mortality rates for white males. Environmental lead levels and PbB levels were available for only about 30% of all workers for varying time periods from 1947 to 1972. Statistically significant increases in mortality from "other hypertensive disease" and "chronic nephritis" were seen in both lead cohorts. Limitations of this study include the fact that various confounding factors, such as smoking, were not accounted for, and the workers were probably exposed to other toxic chemicals. 

Comparison of the relative sediment toxicity of different SPs can be difficult as there are a variety of different test methods and endpoints evaluated, in addition to other confounding factors relating to sediment quality. Amweg et al. [28] determined the toxicity of six SPs to //. azteca in 10-day studies at 23 °C in natural sediments containing 1-6% OC. Toxicity data were reported as bulk sediment concentrations and normalized to the organic carbon content (Table 5). The results indicated that normalization removed some, but not all, of the variability between sediments. Other factors such as sediment texture may also affect bioavailability and hence apparent toxicity in sediment studies. 

AltJiough the demonstration of some degree of maternal toxicity is required in regulatory developmental toxicology studies for both pharmaceuticals and chemicals (1 ), marked maternal toxicity may be a confounding factor in study design and data interpretation. 

Bioassay Detected effects Endpoint Levels Of indication Known active toxic compounds Performance characteristics (sensitivity detection limit variability reproducibility) Confounding factors Percentage false positive data... 

An important complication that is specific to human developmental toxicity studies is the necessity to control for confounding factors that influence human development, such as parental intelligence, quality of home environment, nutritional factors and socioeconomic status (Bellinger et al., 1992 Bellinger, 1995). These may influence the outcomes from the newborn period to adulthood. In addition, assessment methods must take into consideration the time (days, months or years) that may intervene between exposure/insult and the expression of toxicity at a much later age. 

Ankley, G. T., Benoit, D. A., Balogh, J. C., Reynoldson, T. B., Day, K. E. and Hoke, R. A. (1994) Evaluation of potential confounding factors in sediment toxicity tests with three freshwater benthic invertebrates, Environmental Toxicology and Chemistry 13 (4), 627-635. 

Lacey, R., Watzin, M.C. and McIntosh, A.W. (1999) Sediment organic matter content as a confounding factor in toxicity tests with Chironomus tentans, Environmental Toxicology and Chemistry 18 (2), 231-236. 

Sublethal toxicity tests that are relatively less sensitive can reduce the usefulness of both ZPE and LTF. In addition, confounding factors such as the presence of other discharge sources can complicate the interpretation of both hazard assessment schemes. 

We have addressed the topic of metal bioavailability and metal toxicity in environmental samples. Traditionally, metal availability is investigated using a chemical approach. Afterwards, the concept of Water Effect Ratio (WER) was proposed by the U.S. EPA and employed bioassays (e.g., fish and invertebrate tests) to assess metal bioavailability and toxicity. In the HMBC approach discussed in this review, we have made use of a bacterial assay that is specific for metal toxicity to achieve this goal. This is only a preliminary survey of the potential applications of the HMBC concept. Some preliminary results on the use of MetPLATE for the fractionation of HMBC to obtain information on the factor(s) that control metal bioavailability in environmental samples were also presented. Using MetPLATE eliminates or diminishes the confounding factor represented by the presence of organic toxicants in a given sample. Further work is needed to refine the fractionation scheme. 

In summary, other symptoms of IFNa toxicity are far more common than nephrotoxicity (fevers, chills, malaise, arthralgias, fatigue anorexia, weight loss, depression, impaired cognihve function, diminished libido, abnormal thyroid function). Nevertheless, IFNa has a complicated and important relationship to the kidney but there are many confounding factors... 

There are considerable data on the chronic toxicity of NP in laboratory animals. The focus of these investigations has typically been evaluation of the potential reproductive and developmental effects of NP, due to its ability to modulate estrogen receptor-mediated responses. Many endpoints are not consistently observed across studies. Some of this variability may be due to differences in the conditions, design, and other test-specific variables of the toxicity tests. For example, since phytoestrogens are abundant in most laboratory animal feeds (such as found in soy and alfalfa) and are known to modulate estrogen receptor-mediated responses, phytoestrogens may be confounding factors as a result of the feed selection. 

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