Wesley J. Birge

Fish and amphibian embryos--a model system for evaluating teratogenicity.

Developmental stages of fish and amphibians were used to evaluate reproductive impairments produced by environmental contaminants. Using static-renewal and flow-through procedures, exposure was initiated at, or soon after, fertilization and maintained through 4 days posthatching. Trace concentrations of many environmental toxicants produced high frequencies of mortality and teratogenesis. When developmental stages of the trout were exposed to inorganic mercury, 10% control-adjusted mortality was observed at 1 microgram/L and frequencies of terata in hatched populations ranged from 8% to 43% for exposure concentrations of 2 to 25 micrograms/L. In similar tests with the narrow-mouthed toad, 45% mortality occurred when mercury was administered at 1 microgram/L; frequencies of teratogenesis ranged from 8% to 17% at exposure concentrations of 1 to 5 micrograms/L; and complete mortality occurred at 7 micrograms/L. Boron-induced teratogenesis in trout ranged from 5% at 1 microgram/L to 51% at higher exposure levels. When catfish embryos were exposed to atrazine at 0.06, 4.8, and 46.7 mg/L, terata appeared in surviving populations at frequencies of 4%, 69%, and 100%, respectively. Fish and amphibian developmental stages constitute simple and effective models for 1) investigating mechanisms of teratogenesis, 2) evaluating the impact of environmental toxicants on aquatic biota, and 3) identifying environmental teratogens which may be of concern to human health.

Ecology of a saline stream: community responses to spatial gradients of environmental conditions

Spatial changes in structural and functional characteristics of fish and macroinvertebrate communities in eastern Kentucky were investigated in a drainage system chronically exposed to high levels of chloride salts from nearby oilfield operations. Salinity levels at biological monitoring stations ranged from 0.12–31.3‰. Lotic regions with salinities greater than 10‰ were dominated by larvae of the dipterans Ephydra and Culicoides. In regions with salinities less than 10‰ species richness increased more or less linearly with decreasing levels of chloride salts. Ephemeropterans appeared to be one of the major invertebrate groups least tolerant of elevated NaCl levels and were absent in regions with salinities greater than 2‰ Availability of food resources, such as periphyton and particulate organic matter, did not appear to be grossly altered in disturbed regions, and it is suggested that the observed distribution of macroinvertebrate fauna was largely in response to taxonomic differences in salt tolerance. Fish seemed to be more tolerant of highly saline conditions, and several species were observed in regions experiencing salinities as high as 15‰. Accordingly, assemblages of fish taxa along the salinity gradient may have been influenced by trophic factors, such as spatial limitations in availability of invertebrate prey.

Modeling the effects of chronic toxicity on fish populations: the influence of life-history strategies.

Five life-history scenarios were composed to simulate fish population adaptations for survival under various environmental conditions. The scenarios encompassed differences in stage-specific survival, fecundity and hatch success, number of spawning events, and life-span effect response to chronic toxic impacts. The strategies represent a good survivor/generalist (GS), a species exhibiting high young-of-the-year survival, a species exhibiting high adult survival, a species with no parental care or guarding behavior, and an anadromous salmonid strategy. Although the modeled scenarios were similar in population growth rate and imposed toxic effects, differences concerning the influence of various traits were found. Scenarios characterized by a short life span, short time to reproductive maturity, moderate to high survival to reproductive maturity, large number of spawning events, and parental guarding behaviors experienced less perturbation from the imposed chronic stresses. The GS scenario, modeled after the round goby (Neogobius melanostomus), exemplified these characteristics. Scenarios exhibiting little difference between reproductive effort for younger and older adults recovered quickly from stressors on fecundity and adult survival rates. Greater population decline in response to commensurate impacts was seen for life-history strategies with long life span, no parental guarding behaviors, semelparity and annual iteroparity, high adult survival rates, and moderate to low fecundity.

Development of the blood-cerebrospinal fluid barrier to proteins and differentiation of cerebrospinal fluid in the chick embryo

Abstract Blood plasma and cerebrospinal fluid (CSF) samples were collected from chick embryos at 5–20 days of development. Protein concentrations of the samples were determined using Folin phenol reagent. During development plasma protein concentration increases from 4.79 mg/ml at 5 days to 7.07, 9.47, and 18.13 mg/ml by Days 10, 14, and 20, respectively. The protein concentration of CSF increases from 3.25 mg/ml at 5 days to 5.10 mg/ml on Day 10, representing approximately 68–72% as much protein as found in plasma at corresponding embryonic stages. This parallel increase in CSF and plasma protein is particularly significant from 6 to 10 days, when the average gain rates are 0.40 and 0.39 mg/ml/day, respectively. The protein level in CSF remains nearly stable from 10 to 12 days, with a moderate peak occurring on Day 11 (5.32 mg/ml). Thereafter, CSF protein concentration drops from 5.17 mg/ml at 12 days of development to 1.42 mg/ml on Day 20. This amounts to an average decrease of 0.47 mg/ml/day. It appears that the blood-CSF barrier to proteins begins to function by 10–12 days and that CSF protein concentration decreases to the normal definitive range by 20 days of development.

Toxicity of metals to chick embryos

A comparative index to the embryopathic effects of a number of metals which may appear as trace contaminants in avian food sources is given. Chicken eggs (White Plymouth Rock strain) were treated by yolk injection with sodium arsenite, sodium selenate and chloride salts of cadmium, lead, mercury, methyl mercury and zinc immediately prior to incubation. Eggs were positioned horizontally for 24 hr before injection, allowing the embryonic blastodisc to orient away from the point of needle entry. The test aliquot was deposited in a needle track extending through the diameter of each egg yolk, thus facilitating the uniform distribution of the toxicant. Percent survival was determined as hatchability in experimental populations/hatchability of controls. Survival rates at a concentration of 0.001 ppM were 64-66% for selenium, arsenic and cadmium at the same concentration, survival rates were 74-83 percent for lead, methyl mercury, inorganic mercury, and zinc. All metals produced appreciable percentages of teratogenic survivors when administered at or above their TL/sub 50/ concentrations. The greatest percentages of defective survivors were always at the highest test concentrations which permitted survival, ranging from 0.5 ppM for selenium and arsenic to 10.0 ppM for mercury and zinc. (MFB)

Metal trophic transfer from algae to cladocerans and the relative importance of dietary metal exposure

We initially investigated effects and uptake of cadmium and copper on Pseudokirchneriella subcapitata (primary producer; formerly known as Selenastrum capricornutum). Our major efforts focused on the effects of metal-laden (i.e., Cd, Cu) P. subcapitata when used to provide dietary metal exposure to Ceriodaphnia dubia (primary consumer). Major test endpoints included feeding rate, survival, and reproduction. Metal body burden in C. dubia increased dose dependently at dietary exposure concentrations of 0.6 microg/g algal dry weight or less for cadmium and 74.7 microg/g algal dry weight or less for copper. However, it decreased sharply when dietary concentrations exceeded 0.6 microg/g algal dry weight for cadmium and 74.7 microg/g algal dry weight copper. Both dietary cadmium and copper affected all the major test endpoints. Whereas reproduction was observed to be the most sensitive endpoint, survival was observed to be the least sensitive endpoint. These results demonstrated the potential importance of dietary exposure for consideration in metal regulations or risk assessment.

Structure-activity relationships in aquatic toxicology*

Relationships among chemical structure, aquatic toxicity, and bioconcentration potential were examined for several classes of organic compounds. Structure-toxicity correlations were based largely on median lethal concentrations (LC50) and toxicant threshold concentrations (LC1) determined in mini-chronic tests with early life stages of fish and amphibians. Exposure was initiated at fertilization and maintained through 4 days posthatching. Bioconcentration potential was assessed using n-octanol/water partition coefficients (log P). In tests with polychlorinated biphenyls (PCB), acute and chronic toxicity generally increased with percent chlorination. In addition, toxicity of specific PCBs appeared to be affected by the ratio of less chlorinated to more highly chlorinated isomers. The toxicity of chlorinated methanes (i.e., methylene chloride, chloroform, carbon tetrachloride) also increased with chlorination. Concerning single ring aromatic compounds, pyridine was much less toxic than benzene and benzene was less toxic than its mono-substituted derivatives, including chlorobenzene, nitrobenzene, toluene, and phenol. However, no consistent order of toxicity was observed for the substituted compounds. Acute toxicity also increased with the number of aromatic rings in a series of nitrogen heterocyclic compounds, and the latter were less toxic than corresponding alicyclic compounds. Within most classes of compounds, a direct correlation was observed between acute toxicity and bioconcentration potential. As observed with PCB compounds, the mini-chronic test described in this study permitted evaluations of structure-activity relationships using both LC50 and LC1 values determined with early life stages. The LC1s compared well with results obtained in life-cycle studies, thus providing an economical and reliable means of estimating chronic values for reproductive impairment.

An integrated assessment of the biological effects of boron to the rainbow trout

Abstract Acute and chronic toxicity tests have been performed in a number of independent laboratories to assess the effects of boron on aquatic life. Among the lowest effect concentrations were those determined in investigations on embryo-larval stages of the rainbow trout (Oncorhyncus mykiss) in reconstituted water. To gain a more precise definition of effect levels with rainbow trout, additional studies were performed with this species in both laboratory and natural dilution waters. Consistent lowest observed effect concentrations (LOECs) ranged from 0.1 to > 18 mg/L boron. The flat concentration-response curve observed for boron (i.e., small changes in effects relative to large increases in boron concentrations) sometimes affected precision in the determination of no-effect or threshold concentrations. Other factors that may have contributed to the wide range of LOEC values related to the effects of different types of dilution water on boron toxicity and the differential sensitivity of the trout strains evaluated. The impact of these variables on defining effect levels is discussed in detail in this paper. Based on the results of the rainbow trout tests, together with data from field surveys, a concentration of between 0.75 and 1.0 mg/L is determined to be a reasonable, environmentally acceptable limit for boron in aquatic systems. This conclusion is consistent with limits proposed by other investigators.

Effects of cadmium-enriched sediment on fish and amphibian embryo-larval stages

Aquatic toxicity tests were conducted to evaluate the effects of cadmium-enriched sediment on embryo-larval stages of the goldfish (Carassius auratus), leopard frog (Rana pipiens), and largemouth bass (Micropterus salmoides). Natural stream sediment was collected and enriched with cadmium to nominal concentrations of 1.0, 10.0, 100, and 1000 mg/kg. Enriched sediments were placed in Pyrex dishes and covered with 350 ml of reconstituted water. Fertilized eggs were placed in the dishes and maintained through 4 days posthatching, giving a total exposure time of 6 to 7 days. For all tests the cadmium concentrations ranged from 1.1 to 76.5 micrograms/liter in water above sediments containing 1 to 1000 mg Cd/kg, respectively. Although low frequencies of mortality were observed in all tests, goldfish, leopard frog, and bass exposed to sediments enriched to 1000 mg Cd/kg accumulated 4.61, 12.55, and 60.0 micrograms Cd/g, respectively. No significant correlations (P less than 0.05) were found between mortality of the goldfish and leopard frog and the cadmium concentrations in either water or sediment. However, all three species showed strong correlations (r greater than or equal to 0.98) between cadmium concentrations in water and tissue, sediment and tissue, and water and sediment. Tissue cadmium concentrations were related to the length of time test organisms were in direct contact with cadmium-enriched sediment.

Effects of acid-mine drainage on the chemical and biological character of an alkaline headwater stream

Distribution of metals in water and sediments, as well as spatial alteration in the benthic macroinvertebrate and fish assemblages, was assessed in an alkaline headwater stream in eastern Kentucky receiving runoff from an abandoned surface mine. Concentrations of aluminum, copper, iron, manganese, and zinc generally increased 2 to 3 orders of magnitude in the receiving water immediately below where the mine runoff entered the creek. Metals in the water column were transported downstream largely in association with suspended particulates and declined in concentration progressively in a linear fashion commensurate to distance below the mine drainage outfall. In contrast, metal enrichment of sediments occurred spatially in a non-incremental pattern and varied among locations in conjunction with sitespecific changes in concentration levels of sediment organic matter. Benthic macroinvertebrate and fish fauna were eliminated for a distance of 0.3 km below the outfall, presumably owing to the presence of high levels of dissolved metals and low pH. Recovery of stream benthos occurred 1.0–2.0 km further downstream and was characterized by numerical dominance of collector-gatherer trophic groups consisting primarily of midge larvae (Chironomidae: Orthocladiini). Fish fauna in downstream reaches consisted exclusively of creek chubs(Semotilus atromaculatus) and stoneroller minnows(Campostoma anomalum). Metal levels in water and sediments remained elevated in regions of biological recovery and, as a consequence, downstream communities were comprised predominantly of metal tolerant taxa.