Peter G. Meier

Development of Bayesian Monte Carlo techniques for water quality model uncertainty

A new technique, Bayesian Monte Carlo (BMC), is used to quantify errors in water quality models caused by uncertain parameters. BMC also provides estimates of parameter uncertainty as a function of observed data on model state variables. The use of Bayesian inference generates uncertainty estimates that combine prior information on parameter uncertainty with observed variation in water quality data to provide an improved estimate of model parameter and output uncertainty. It also combines Monte Carlo analysis with Bayesian inference to determine the ability of random selected parameter sets to simulate observed data. BMC expands upon previous studies by providing a quantitative estimate of parameter acceptability using the statistical likelihood function. The likelihood of each parameter set is employed to generate an n-dimensional hypercube describing a probability distribution of each parameter and the covariance among parameters. These distributions are utilized to estimate uncertainty in model predictions. Application of BMC to a dissolved oxygen model reduced the estimated uncertainty in model output by 72% compared with standard Monte Carlo techniques. Sixty percent of this reduction was directly attributed to consideration of covariance between model parameters. A significant benefit of the technique is the ability to compare the reduction in total model output uncertainty corresponding to: (1) collection of more data on model state variables, and (2) laboratory or field studies to better define model processes. Limitations of the technique include computational requirements and accurate estimation of the joint probability distribution of model errors. This analysis was conducted assuming that model error is normally and independently distributed.

Xenobiotic-induced apoptosis: significance and potential application as a general biomarker of response

The process of apoptosis, often coined programmed cell death, involves cell injury induced by a variety of stimuli including xenobiotics and is morphologically, biochemically, and physiologically distinct from necrosis. Apoptotic death is characterized by cellular changes such as cytoplasm shrinkage, chromatin condensation, and plasma membrane asymmetry. This form of cell suicide is appealing as a general biomarker of response in that it is expressed in multiple cell systems (e.g. immune, neuronal, hepatal, intestinal, dermal, reproductive), is conserved phylogenetically (e.g. fish, rodents, birds, sheep, amphibians, roundworms, plants, humans), is modulated by environmentally relevant levels of chemical contaminants, and indicates a state of stress of the organism. Further, apoptosis is useful as a biomarker as it serves as a molecular control point and hence may provide mechanistic information on xenobiotic stress. Studies reviewed here suggest that apoptosis is a sensitive and early indicator of acute ...The process of apoptosis, often coined programmed cell death, involves cell injury induced by a variety of stimuli including xenobiotics and is morphologically, biochemically, and physiologically distinct from necrosis. Apoptotic death is characterized by cellular changes such as cytoplasm shrinkage, chromatin condensation, and plasma membrane asymmetry. This form of cell suicide is appealing as a general biomarker of response in that it is expressed in multiple cell systems (e.g. immune, neuronal, hepatal, intestinal, dermal, reproductive), is conserved phylogenetically (e.g. fish, rodents, birds, sheep, amphibians, roundworms, plants, humans), is modulated by environmentally relevant levels of chemical contaminants, and indicates a state of stress of the organism. Further, apoptosis is useful as a biomarker as it serves as a molecular control point and hence may provide mechanistic information on xenobiotic stress. Studies reviewed here suggest that apoptosis is a sensitive and early indicator of acute and chronic chemical stress, loss of cellular function and structure, and organismal health. Examples are provided of the application of this methodology in studies of health of lake trout (Salvelinus namaycush) in the Laurentian Great Lakes.

Rapid toxicity testing based on yeast respiratory activity.

Rapid and economical techniques are needed to determine the effects of environmental contaminants. At present, the main methods to assess the impact of pollutants are based on chemical analysis of the samples. Invertebrate and vertebrate exposures have been used over the last two decades in assessing acute and chronic toxicities. However, these tests are labor intensive and require several days to complete. An alternative to whole organism exposure is to determine toxic effects in monocellular systems. Another approach for assessing toxicity is to monitor sensitive, nonspecific, subcellular target sites such as mitochondria. Changes in mitochondrial function which could indicate a toxic effect can be demonstrated readily after addition of a foreign substance. In initial assessments of various chemicals, rat liver mitochondria (RLM) were evaluated as a biological sensor of toxicity. False toxicity assessments will result if these ions are present even though they are generally considered nontoxic. Because of these disadvantages, an alternative mitochondrial system, such as found in bakers yeast, was evaluated.

Organochlorine pesticide residues in rice paddies in Malaysia, 1981

Rice and fish are common staple foods in many parts of Asia, Africa, and Latin America. The cultivation of fish in paddy fields has proven to be highly productive. Simultaneous rice and fish cultures can be accomplished with little extra effort and is economically feasible and practical. Fish enhance rice yield through predation of insect pests, reduce aquatic vascular plant and algal growth, and add nutrients through deposition of fecal matter (TAN et al. 1973). However, the present use of persistent and toxic pesticides in paddy fields may not only destroy the ecological relationship between rice and fish, but may even prove deleterious to the consumers. In order to assess the potential health implications to paddy farmers, this study was conducted to determine the indigenous concentrations of organochlorine pesticides in the paddy fish, sediment, and water.

Interlaboratory precision study of a whole sediment toxicity test with the bioluminescent bacterium Vibrio fischeri

The reproducibility of sediment toxicity bioassays using the Microtox® solid‐phase test (SPT) with the luminescent bacterium Vibrio fischeri was estimated in an interlaboratory precision study. A preliminary study, with five labs testing six solid‐phase samples, was used to evaluate proposed method modifications. As a result, it was recommended that the SPT protocol be revised to include whole sample testing with subsequent wet‐weight to dry‐weight correction, and the use of NaNO3, rather than NaCl, as the diluent for freshwater sediment samples. The revised protocol was then examined in a definitive precision study, with 18 laboratories each testing eight samples. Coefficients of variation for the eight samples ranged from 35.8 to 78.0%. One possible source of error is the separate moisture content determination performed by each laboratory in order to calculate the wet‐weight to dry‐weight correction. Out of a total of 143 bioassays performed by the 18 labs, only two results (1.4%) exceeded the critical value of the interlaboratory consistency statistic h. With coefficients of variation comparable to other interlaboratory precision studies, and an extremely low number of results exceeding the critical value of h, it is concluded that the V. fischeri SPT has an acceptable level of precision and can be developed as a standardized test method. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 339–345, 1999

ACUTE TOXICITY OF SOME BLUEGREEN ALGAE TO THE PROTOZOAN PARAMECIUM CAUDATUM1

Four species of bluegreen algae were tested for possible effect on the protozoan Paramecium caudatum Ehrenberg. Toxicity was demonstrated using lyophilized cells of Fischerella epiphytica Ghose and Gloeotrichia echinulata (Smith) Richter. Nostoc linckia (Roth) Bornet & Thuret failed to show any effects when lyophilized but became toxic when sonified. Anabaena flos‐aquae (Lyngb.) Bréb. was nontoxic in all tests. G. echinulata was lethal at 0.1 mg·ml−1 which is comparable to the toxic concentration of Aphanizomenon flos‐aquae (L.) Ralfs reported for microcrustaceans.

Acute and chronic life cycle toxicity of acenaphthene and 2,4,6-trichlorophenol to the midge Paratanytarsus parthenogeneticus (Diptera: Chironomidae).

The acute and life cycle toxicities of acenaphthene and 2,4,6-trichlorophenol (2,4,6-TCP) were evaluated using the parthenogenic dipteran larva, Paratanytarsus parthenogeneticus, of the family Chironomidae. Static 48 h acute toxicity tests employed third instar larvae, and the flow-through 20-day life cycle tests were initiated with eggs. No acute lethal effect was observed in the saturated concentration (2.1 mg/l) of acenaphthene in water, and the median lethal concentration of 2,4,6-TCP was approximately 40 mg/l. In the life cycle toxicity test with acenaphthene, hatchability of the midge was affected by 50% at an exposure concentration of approximately 0.17 mg/l. The median effective concentration for larval, pupal and adult development was found between 0.06 and 0.07 mg/l, respectively, and these were significantly lower than the effective concentration for hatching success. With regard to 2,4,6-TCP toxicity, the median effective concentration for midge hatchability was 4.23 mg/l. The larval development, pupal formation and adult emergence, however were impeded at 1.60, 1.46 and 1.33 mg/l, respectively. Each level was noticeably lower than the median effective concentration for hatchability. The concentrations for each compound that interfered with the development to fourth instar, pupa and adult were not significantly different. These results indicate that larval developments after hatching were the most sensitive stages and affected the success of midge growth.

Oil and PCB interactions on the uptake and excretion in midges

Polychlorinated biphenyls (PCBs) are highly persistent global contaminants with a broad range of long-term environmental and health effects (Fishbein 1974). Body burdens of many chlorinated aryl compounds in aquatic organisms accumulate by combinations of passive absorption directly from water or by partitioning into lipids of foods. Both routes have been shown to contribute significantly to levels found in fish (Stalling and Mayer 1972; Hansen et al. 1976).

Artificial substrata for reducing periphytic variability on replicated samples

Periphyton accrual (chlorophyll a) was evaluated utilizing two different geometrically shaped artificial glass substrata. The first consisted of small coverslips attached to a glass slide (Dilks & Meier 1981), while the other method employed both horizontally and vertically oriented small culture tubes. Sufficient numbers of each type were placed in Fleming Creek (Ann Arbor, Michigan), a second order temperate stream, to permit four collections of three replicates for each type at 5-day intervals. With the exclusion of the first collection (after 5 days), the variability among the replicates was less than 8 percent. Analysis of the chlorophyll a data by ANOVA and simple linear regression showed least amount of variation in horizontally positioned test tubes, followed by those of vertical orientation, and then by the coverslips. The highest concentration of periphyton biomass measured in chlorophyll a was, however, observed in the vertically placed test tubes. The coverslips and horizontally incubated tubes collected comparable concentrations of chlorophyll a over the exposure period.

Sabotage of Public Water Supply Systems

During times of war, there is always talk of threats cf terrorism against public water supplies. In the recent Gulf War, a number of utilities in the U.S. stepped up their security measures by guarding their treatment plants and distribution systems (AWWA, 1991). Special security procedures were in place during the Olympic Games in both Los Angeles and Atlanta.