SEARCH · USGS Science

Results for “Experimental Results”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 811 records · Page 45Linked to original sources

USGS1997

An evaluation of the rust fungus Gymnoconia nitensas a potential biological control agent for alien Rubus species in Hawaii

The rust fungus Gymnoconia nitens infects blackberry ( Rubus argutus ) systemically in regions of the continental United States, producing bright yellow–orange masses of spores on newly developing floricanes during springtime. In tests to determine the suitability of this rust as a biological control agent for R. penetrans in Hawaii, a species now thought to be conspecific with R. argutus, rooted cuttings of the Hawaiian plants were grown at North Carolina State University, inoculated, and observed. Other introduced weedy Rubus spp. in Hawaii, including R. ellipticus, R. rosifolius, and R. glaucus, as well as the two endemic species R. hawaiensis and R. macraei, also were inoculated. No species of Rubus are of commercial importance in Hawaii, but the protection of the native species, of which R. macraei is rare, was of utmost concern. The native Hawaiian species did not survive well in North Carolina in this study, however. Later availability of a plant pathogen containment laboratory in Hawaii enabled similar tests to be conducted at that facility. In addition to the above species, R. spectabilis (salmonberry), a species native to the Pacific Northwest with which the Hawaiian Rubus spp. are thought to share a common ancestor, was inoculated in Hawaii. Infection with G. nitens under natural field conditions becomes apparent only when sporulation occurs on floricanes the second year following infection. However, experimental inoculation led to early responses of chlorotic leaf flecking and puckering, leaf and stem contortion, and stem gall formation, indicating the sensitivity of R. penetrans (= R. argutus ), R. hawaiensis, and R. macraei to this rust. Apparent systemic infection also resulted in sporulation on one plant of R. macraei. Ability to attack the endemic species suggests that G. nitens would not be suitable for release in Hawaii as a biological control agent, at least on the islands with populations of the native species.

Hawaii↗

USGS1980

Kinetic model for the short-term dissolution of a rhyolitic glass

Aqueous dissolution experiments with the vitric phase of a rhyolitic tuff were performed at 25??C and constant pH in the range 4.5-7.5. Results suggest interchange of aqueous hydrogen ions for cations situated both on the surface and within the glass. At time intervals from 24 to 900 hr., dissolution kinetics are controlled by ion transport to and from sites within the glass. Experimental data indicate that parabolic diffusion rate of a chemical species from the solid is a nonlinear function of its aqueous concentration. A numerical solution to Fick's second law is presented for diffusion of sodium, which relates it's aqueous concentration to it's concentration on glass surface, by a Freundlich adsorption isotherm. The pH influence on sodium diffusion in the model can be accounted for by use of a pH-dependent diffusion coefficient and a pH-independent adsorption isotherm. ?? 1980.

Chemical Geology↗

USGS1986

The system NaCl-H 2 O: relations of vapor-liquid near the critical temperature of water and of vapor-liquid-halite from 300° to 500°C

Vapor-liquid relations ( P - T - x ) for the system NaCl-H 2 O were determined experimentally at temperatures spanning the critical temperature of water ( T c ), the lowest temperature in the system at which critical behavior occurs. In addition, vapor-liquid-halite P - T - x (vapor) relations were determined from 300° to 500°C. Results show that at 373.0°C, immediately below T c , the vapor side of the isothermal vaporliquid P-x boundary has a shape quite different from that previously conceived. The NaCl content of the vapor increases with pressure in a smooth manner from the pressure of the three-phase assemblage (135 bars, 0.0029% NaCl), to a pressure just below that of the vapor pressure of pure water (0.012% NaCl at 184 bars). Above this pressure the boundary abruptly reverses and projects asymptotically to 0% NaCl in a beak-like shape at 218 bars, the vapor pressure of pure water. At 375.5°, slightly above T c , the asymptote disappears, and is replaced by a rounded nose. At progressively higher temperatures, the nose disappears and by 380°C the familiar symmetrical bell-shaped curve predominates with the critical point defined by the top of the bell. The P - T curve of the three-phase assemblage determined in the present study is in agreement with previous workers. The NaCl content of the three-phase vapor, however, is much higher than some literature values at temperatures above 410°C.

Geochimica et Cosmochimica Acta↗

USGS2021

Performance of the ecosystem demography model (EDv2.2) in simulating gross primary production capacity and activity in a dryland study area

Dryland ecosystems play an important role in the global carbon cycle, including regulating the inter-annual global carbon sink. Dynamic global vegetation models (DGVMs) are essential tools that can help us better understand carbon cycling in different ecosystems. Currently, there is limited knowledge of the performance of these models in drylands partly due to characterizing the heterogeneity of the vegetation and hydrometeorological conditions. The aim of this study is to evaluate the performance of a DGVM for drylands to facilitate improved understanding of gross primary production (GPP) as one of the important components of the carbon cycle. We performed a sensitivity analysis and calibrated the Ecosystem Demography (EDv2.2) DGVM to simulate GPP in a dryland watershed (Reynolds Creek Experimental Watershed, Idaho) in the western US for the years 2000-2017. GPP capacity and activity were investigated by comparing model simulations with GPP estimated from eddy covariance data (available from 2015-2017) and remote sensing products (2000-2017). Our results show good performance of EDv2.2 at daily timesteps ( R M S E ≈ 0.38 [ kgC / m 2 / year ] ) "> RMSE≈0.38[kgC/m2/year])

Idaho↗

USGS2008

Assessment of crop growth and soil water modules in SWAT2000 using extensive field experiment data in an irrigation district of the Yellow River Basin

SWAT, a physically-based, hydrological model simulates crop growth, soil water and groundwater movement, and transport of sediment and nutrients at both the process and watershed scales. While the different versions of SWAT have been widely used throughout the world for agricultural and water resources applications, little has been done to test the performance, variability, and transferability of the parameters in the crop growth, soil water, and groundwater modules in an integrated way with multiple sets of field experimental data at the process scale. Using an multiple years of field experimental data of winter wheat (Triticum aestivum L.) in the irrigation district of the Yellow River Basin, this paper assesses the performance of the plant-soil-groundwater modules and the variability and transferability of SWAT2000. Comparison of the simulated results by SWAT to the observations showed that SWAT performed quite unsatisfactorily in LAI predictions during the senescence stage, in yield predictions, and in soil-water estimation under dry soil-profile conditions. The unsatisfactory performance in LAI prediction might be attributed to over-simplified senescence modeling; in yield prediction to the improper computation of the harvest index; and in soil water under dry conditions to the exclusion of groundwater evaporation from the soil water balance in SWAT. In this paper, improvements in crop growth, soil water, and groundwater modules in SWAT were implemented. The saturated soil profile was coupled to the oscillating groundwater table. A variable evaporation coefficient taking into account soil water deficit index, groundwater depth, and crop root depth was used to replace the fixed coefficient in computing groundwater evaporation. The soil water balance included the groundwater evaporation. The modifications improved simulations of crop evapotranspiration and biomass as well as soil water dynamics under dry soil-profile conditions. The evaluation shows that the crop growth and soil water components of SWAT could be further refined to better simulate the hydrology of agricultural watersheds. ?? 2008 Elsevier B.V. All rights reserved.

Journal of Hydrology↗

USGS2026

Arctic Grayling, scared to death: Are Brown Trout an impediment to Arctic Grayling reintroduction success in Michigan?

Introduction: Arctic Grayling Thymallus arcticus were extirpated from Michigan in 1936. Their demise was caused by over-fishing, habitat destruction from large-scale logging, and Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta. Subsequently, Brook and Brown trout have become the dominant salmonid species in Michigan streams. Past attempts to restore Grayling to Michigan have been unsuccessful perhaps due to competition with these now resident salmonids. Objective: To determine the impacts of competition between age-0 Arctic Grayling and age-0 Brook and Brown Trout on Grayling growth and survival. Methods: Competition trials were performed in experimental streams, lasting two months, across three years, with three treatment types: the control, 10 Grayling with 10 Grayling; the Brook Trout treatment, 10 Grayling with 10 Brook Trout; and the Brown Trout treatment, 10 Grayling with 10 Brown Trout. Results: Brown Trout had a significant effect on Arctic Grayling growth and mortality, while Brook Trout had no effect on Arctic Grayling growth or mortality. Conclusion: Age-0 Brown Trout negatively impacted growth, condition, and survival of age-0 Arctic Grayling, while the impacts of age-0 Brook Trout or conspecifics were negligible. This suggests reintroduction of Arctic Grayling may be more successful in streams with few or no Brown Trout.

Michigan↗

USGS2008

Is there enough sand? Evaluating the fate of Grand Canyon sandbars

Large dams have the potential to dramatically alter the flow regime, geomorphology, and aquatic ecosystem of downstream river reaches. Development of flow release regimes in order to meet multiple objectives is a challenge facing dam operators, resource managers, and scientists. Herein, we review previous work and present new analyses related to the effects of Glen Canyon Dam on the downstream reach of the Colorado River in Marble and Grand Canyons. The dam traps the entire incoming sediment load in Lake Powell and modulates the hydrologic regime by, for example, eliminating spring snowmelt floods, resulting in changes in the geomorphology of the river downstream. The primary geomorphic impact has been the erosion of sandbars along the banks of the river. Recognition of this impact has led to many scientific studies and a variety of experimental operations of Glen Canyon Dam with the goal of rebuilding the eroding sandbars. These efforts have thus far been generally unsuccessful and the question remains as to whether or not the dam can be operated such that sandbars can be rebuilt and maintained over extended periods with the existing sediment supply. We attempt to answer this question by evaluating a dam operation that may be considered a "best-case scenario" for rebuilding and maintaining eroded sandbars. Our analysis suggests that this best-case scenario may indeed have viability for rebuilding sandbars, and that the initial rate at which sandbars could be rebuilt is comparable to the rate at which sandbars have been eroded since dam construction. The question remains open as to the viability of operations that deviate from the best-case scenario that we have defined.

Grand Canyon↗

USGS2010

Application of SEAWAT to select variable-density and viscosity problems

SEAWAT is a combined version of MODFLOW and MT3DMS, designed to simulate three-dimensional, variable-density, saturated groundwater flow. The most recent version of the SEAWAT program, SEAWAT Version 4 (or SEAWAT_V4), supports equations of state for fluid density and viscosity. In SEAWAT_V4, fluid density can be calculated as a function of one or more MT3DMS species, and optionally, fluid pressure. Fluid viscosity is calculated as a function of one or more MT3DMS species, and the program also includes additional functions for representing the dependence of fluid viscosity on temperature. This report documents testing of and experimentation with SEAWAT_V4 with six previously published problems that include various combinations of density-dependent flow due to temperature variations and/or concentration variations of one or more species. Some of the problems also include variations in viscosity that result from temperature differences in water and oil. Comparisons between the results of SEAWAT_V4 and other published results are generally consistent with one another, with minor differences considered acceptable.

Scientific Investigations Report↗

USGS1989

Developments in the control of bacterial kidney disease of salmonid fishes

Bacterial kidney disease of salmonid fishes, caused by Renibactenum salrnoninarum, was first reported more than 50 yr ago; nevertheless, large gaps persist in our knowledge of the infection - particularly in methods for its control. In the 1950's, principal control measures consisted of prophylactic or therapeutic feeding of sulfonamides, which were later supplanted by the antibiotic erythromycin. Chemotherapy has effected some reduction of mortality, but benefits are typically transient and mortality usually resumes after the drug is withdrawn. Some studies have indicated that diet composition affects the prevalence and severity of the disease. Although tests of chemotherapeutants and diet modification have continued, research emphasis has shifted partly toward prevention of the disease by breaking the infection cycle. It is now generally accepted that R. salrnoninarum can be transmitted both vertically and horizontally. Experimental evidence indicates that immersion of newly fertilized eggs in iodophor or erythromycin does not prevent vertical transmission. However, the injection of female salmon with erythromycin before they spawn shows promise as a practical means of interrupting vertical transmission. The results of attempts to prevent infection of juvenile salmonids by vaccination against bacterial kidney disease have been disappointing, thus underscoring a basic need for a better understanding of protective mechanisms in salmonids. The recent development of more sensitive and quantitative detection methods should aid in evaluating the efficacy of current and future control strategies.

Diseases of Aquatic Organisms↗

USGS2003

The debris-flow rheology myth

Models that employ a fixed rheology cannot yield accurate interpretations or predictions of debris-flow motion, because the evolving behavior of debris flows is too complex to be represented by any rheological equation that uniquely relates stress and strain rate. Field observations and experimental data indicate that debris behavior can vary from nearly rigid to highly fluid as a consequence of temporal and spatial variations in pore-fluid pressure and mixture agitation. Moreover, behavior can vary if debris composition changes as a result of grain-size segregation and gain or loss of solid and fluid constituents in transit. An alternative to fixed-rheology models is provided by a Coulomb mixture theory model, which can represent variable interactions of solid and fluid constituents in heterogeneous debris-flow surges with high-friction, coarse-grained heads and low-friction, liquefied tails. ?? 2003 Millpress.

Conference Paper↗

USGS2020

Nest predation and adult mortality relationships with post-natal metabolic rates and growth among songbird species

Metabolism is thought to mediate the connection between environmental selection pressures and a broad array of life history tradeoffs, but tests are needed. High juvenile predation correlates with fast growth, which may be achieved via fast juvenile metabolism. Fast offspring metabolism and growth can create physiological costs later in life that should be minimized in species with low adult mortality. Yet, relationships between juvenile metabolism and mortality at offspring versus adult stages are unexplored. We found that post-natal metabolism was positively correlated with adult mortality but not nest predation rates among 43 songbird species on three continents. Nest predation, but not adult mortality, explained additional variation in growth rates beyond metabolism. Our results suggest that metabolism may not be the mechanism underlying the relationships between growth and mortality at different life stages.

Journal of Experimental Biology↗

USGS2022

Mississippi Kite nest defense: Is there an influence of nest phenology or human activity?

Birds that have adapted to urban landscapes often display changes in their behavioral responses to human disturbance. This habituation may result in a decreased wariness and secrecy near their nest and an increased inclination to engage in aggressive nest defenses. Aggressive defense of nests has been noted among Mississippi Kites ( Ictinia mississippiensis ), a raptor that has become a common and abundant urban nesting species across the Southern Great Plains. Defensive behaviors include swoops at, and occasional physical contact with, humans who venture close to nests. Previous research found aggressive responses by kites in 16–20% of experimental passes under nests. However, the type of human pedestrian activity around nests may influence the occurrence of aggressive responses. We assessed adult Mississippi Kite responses to experimental nest area intrusions during each week of the first four weeks of nestling development to explore increases or attenuation of aggressive behaviors. We also assessed responses in context of three types of pedestrian passes to nests. We conducted 84 trials consisting of 252 passes and found 90% elicited no response from the attending kite, 8% elicited a flight response, and 2% elicited an attack. There was no difference in response to pass type, but we found evidence that responsiveness may be associated with nestling age. Our results suggest aggression by Mississippi Kites is uncommon, but infrequent events that gain local attention may increase the perceived risk from the species due to the availability heuristic. Additionally, individual nesting pairs may tend toward aggression and become persistent nuisance birds that gain attention but are not representative of the majority of nesting pairs.

Journal of Raptor Research↗

USGS2025

Predicting pup-rearing habitat for Mexican wolves

Population monitoring is essential to document recovery efforts for threatened and endangered species. Mexican wolves ( Canis lupus baileyi ) are an endangered subspecies of gray wolves that historically occupied large portions of the American Southwest and Mexico. Recently, the Mexican wolf population in the United States has been growing rapidly and traditional approaches for population monitoring (e.g., capture and radio collaring) are becoming difficult and expensive as wolves expand into new areas. We developed predictive models of pup-rearing habitat (i.e., den and rendezvous sites) that could help guide future population monitoring efforts. We located 255 den sites and 129 rendezvous sites in Arizona and New Mexico, USA (1998–2023) using tracking collars and site visits. We sampled habitat conditions in wolf-occupied regions of Arizona and New Mexico and fit logistic regressions to these data following a use–available study design to estimate resource selection functions (RSF) for den and rendezvous sites. We hypothesized wolves would select areas that offered greater physical protection, lower human-disturbance, and access to reliable water sources for pup-rearing but that the relative importance of these features would differ between the denning and rendezvous site seasons. Mexican wolves selected den sites at higher elevations in steeper and rougher terrain that were closer to permanent waterbodies but farther from rural roads. Selection of rendezvous sites was also associated with higher elevations and proximity to waterbodies but varied with availability of green leaf biomass on the landscape. While still highly predictive, our rendezvous site model was less predictive than our den model (Spearman's correlation averaged 0.81 [SE = 0.05] vs. 0.90 [SE = 0.03], respectively), possibly because water and green leaf biomass are more spatially diffuse and variable because of monsoonal rains during the rendezvous site season. Our results suggest that terrain features associated with physical protection and access to reliable water were most important in characterizing suitable pup-rearing habitat for Mexican wolves. By predicting suitable den and rendezvous site habitat across portions of the Mexican Wolf Experimental Population Area, our models can help guide future population monitoring by reducing the total search area when surveying for wolves and increase the probability of detecting all members of a pack.

Arizona, New Mexico↗

USGS2025

Utility of a swath laser rangefinder for characterizing mass movement flow depth and landslide initiation

Mass movements such as debris flows and landslides are some of the deadliest and most destructive natural hazards occurring mostly in alpine and volcanic settings. With ever-growing populations located downslope from known debris flow channels, early warning systems can help prevent loss of life. Geophysical and technological advances have improved monitoring and detection capabilities in recent years; however, they can often be cost prohibitive and resource intensive, making them less accessible to disadvantaged populations. We tested and validated a readily available and cost-effective two-dimensional swath laser rangefinder in a controlled experimental setting against two independent flow-depth lasers. The swath laser successfully recorded cross-sectional changes in flow depth from four debris flows and a water-only flood, in addition to geomorphic changes associated with landslide initiation. The results suggest that a swath laser could be integrated into systems for debris flow detection and characterization of mass movements in natural settings, thus improving the ability to monitor these hazards.

Landslides↗

USGS2009

Investigation of uptake and retention of atmospheric Hg(II) by boreal forest plants using stable Hg isotopes

Although there is now a general consensus among mercury (Hg) biogeochemists that increased atmospheric inputs of inorganic Hg(II) to lakes and watersheds can result in increased methylmercury (MeHg) concentrations in fish, researchers still lack kinetic data describing the movement of Hg from the atmosphere, through watershed and lake ecosystems, and into fish. The use of isotopically enriched Hg species in environmental studies now allows experimentally applied new Hg to be distinguished from ambient Hg naturally present in the system. Four different enriched stable Hg(II) isotope “spikes” were applied sequentially over four years to the ground vegetation of a microcatchment at the Experimental Lakes Area (ELA) in the remote boreal forest of Canada to examine retention of Hg(II) following deposition. Areal masses of the spikes and ambient THg (all forms of Hg in a sample) were monitored for eight years, and the pattern of spike retention was used to estimate retention of newly deposited ambient Hg within the ground vegetation pool. Fifty to eighty percent of applied spike Hg was initially retained by ground vegetation. The areal mass of spike Hg declined exponentially over time and was best described by a first-order process with constants ( k ) ranging between 9.7 × 10 −4 day −1 and 11.6 × 10 −4 day −1 . Average half-life ( t 1/2 ) of spike Hg within the ground vegetation pool (±S.D.) was 704 ± 52 days. This retention of new atmospheric Hg(II) by vegetation delays movement of new Hg(II) into soil, runoff, and finally into adjacent lakes. Ground-applied Hg(II) spikes were not detected in tree foliage and litterfall, indicating that stomatal and/or root uptake of previously deposited Hg (i.e., “recycled” from ground vegetation or soil Hg pools) were likely not large sources of foliar Hg under these experimental conditions.

Environmental Science & Technology↗

USGS2024

Detection of prions from spiked and free-ranging carnivore feces

Chronic wasting disease (CWD) is a highly contagious, fatal neurodegenerative disease caused by infectious prions (PrP CWD ) affecting wild and captive cervids. Although experimental feeding studies have demonstrated prions in feces of crows ( Corvus brachyrhynchos ), coyotes ( Canis latrans ), and cougars ( Puma concolor ), the role of scavengers and predators in CWD epidemiology remains poorly understood. Here we applied the real-time quaking-induced conversion (RT-QuIC) assay to detect PrP CWD in feces from cervid consumers, to advance surveillance approaches, which could be used to improve disease research and adaptive management of CWD. We assessed recovery and detection of PrP CWD by experimental spiking of PrP CWD into carnivore feces from 9 species sourced from CWD-free populations or captive facilities. We then applied this technique to detect PrP CWD from feces of predators and scavengers in free-ranging populations. Our results demonstrate that spiked PrP CWD is detectable from feces of free-ranging mammalian and avian carnivores using RT-QuIC. Results show that PrP CWD acquired in natural settings is detectable in feces from free-ranging carnivores, and that PrP CWD rates of detection in carnivore feces reflect relative prevalence estimates observed in the corresponding cervid populations. This study adapts an important diagnostic tool for CWD, allowing investigation of the epidemiology of CWD at the community-level.

Scientific Reports↗

USGS2012

Frictional slip of granite at hydrothermal conditions

Sliding on faults in much of the continental crust likely occurs at hydrothermal conditions, i.e., at elevated temperature and elevated pressure of aqueous pore fluids, yet there have been few relevant laboratory studies. To measure the strength, sliding behavior, and friction constitutive properties of faults at hydrothermal conditions, we slid laboratory granite faults containing a layer of granite powder (simulated gouge). Velocity stepping experiments were performed at temperatures of 23° to 600°C, pore fluid pressures P H 2 O of 0 (“dry”) and 100 MPa (“wet”), effective normal stress of 400 MPa, and sliding velocities V of 0.01 to 1 μm/s (0.32 to 32 m/yr). Conditions were similar to those in earlier tests on dry granite to 845°C by Lockner et al. (1986). The mechanical results define two regimes. The first regime includes dry granite up to at least 845° and wet granite below 250°C. In this regime the coefficient of friction is high (μ = 0.7 to 0.8) and depends only modestly on temperature, slip rate, and P H 2 O . The second regime includes wet granite above ∼350°C. In this regime friction decreases considerably with increasing temperature (temperature weakening) and with decreasing slip rate (velocity strengthening). These regimes correspond well to those identified in sliding tests on ultrafine quartz. We infer that one or more fluid-assisted deformation mechanisms are activated in the second, hydrothermal, regime and operate concurrently with cataclastic flow. Slip in the first (cool and/or dry) regime is characterized by pervasive shearing and particle size reduction. Slip in the second (hot and wet) regime is localized primarily onto narrow shear bands adjacent to the gouge-rock interfaces. Weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide, or from a dependence of strength on gouge particle size. Major features of the granite data set can be fit reasonably well by a rate- and temperature-dependent, three-regime friction constitutive model (Chester, this issue). We extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural, slipping faults for sliding rates as low as 31 mm/yr. We do this for two end-member cases. In the first case, pore pressure is assumed hydrostatic at all depths. Shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data, while at depths below about 9–13 km (depending on slip rate), strength becomes less sensitive to depth but sensitive to slip rate. In the second case, pore pressure is assumed to be near-lithostatic at depths below ∼5 km. Strength is low at all depths in this case (<20 MPa, in agreement with observations of “weak” faults such as the San Andreas). The predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm/yr, in rough agreement with the seismic-aseismic transition depth observed on mature continental faults. These results highlight the importance of fluid-assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry, large displacements, higher concentrations of phyllosilicates, and time-dependent fault healing.

Journal of Geophysical Research↗

USGS1972

Biological data on PCBs in animals other than man

SUMMARY: Polychlorinated biphenyls have become ubiquitous in the world ecosystem in quantities similar to those of DDE. Experimental studies have shown that PCBs have a toxicity to mallards, pheasants, bobwhite quail, coturnix quail, red-winged blackbirds, starlings, cowbirds, and grackles that is of the same order as the toxicity of DDE to these species. Overt signs of poisoning also are similar to those caused by compounds of the DDT group. Toxic effects of DDE and Aroclor 1254 to coturnix chicks were additive, but not synergistic. PCBs containing higher percentages of chlorine are more toxic to birds than those containing lower percentages. PCBs of foreign manufacture contained contaminants to an extent that greatly increased their toxicity. Residues of PCBs in the brains of birds killed by these compounds measure in the hundreds of parts per million. PCBs may have contributed to mortality of some birds in the field. Toxicity to insects of PCBs of different degrees of chlorination is the reverse of the pattern in birds: the lower chlorinations are more toxic to insects. PCBs enhanced the toxicity of dieldrin and DDT to insects. Shrimp are very sensitive to PCBs and most will die as a result of 20-day exposure to a concentration of 5 ppb. PCBs also inhibit shell growth of oysters. Crabs are less sensitive; all accumulate residues to many times the concentrations in the water, and a test with crabs showed that they lost the residues very slowly. Growth of certain species of marine diatoms was experimentally inhibited by PCBs, but algae were not affected. The small marine crustacean, Gammarus, is sensitive to PCBs in concentrations of thousandths to tenths of a part per billion. Exposure to 5 ppb of Aroclor 1254 caused mortality of two species of fish in 14-45 days. Onset of death was delayed and was accompanied by fungus-like lesions. Rainbow trout were quickly killed by terphenyls at 10 ppb under normal oxygen conditions and at 2 ppb with reduced oxygen. Metabolic changes of PCBs have been suggested by environmental observations of different isomeric patterns in animals of different trophic levels. Quantitative differences also are pronounced, with magnifications of hundreds to thousands of times. Laboratory studies have shown no metabolic changes of PCBs by crabs and shrimps, minimal changes by fish, and pronounced changes by birds. PCBs induce microsomal enzyme activity in birds. Exposure to PCBs increased the susceptibility of mallard ducklings to duck hepatitis virus. Offspring of pheasants whose parents received high dosages of PCBs made poor choices in visual cliff tests. Egg production and hatching after pipping also were affected. Migratory restlessness was increased in English robins exposed to PCBs. Long-term studies of the reproductive effects of Aroclor 1254 on mallards and bobwhite quail and of Aroclor 1254 plus DDE on quail showed no significant differences from controls. In studies of chickens, however, egg production and hatchability were impaired by high doses of Aroclor 1254 and by low doses of Aroclor 1242. Statistical evaluations of the role that different chemicals may play in thinning eggshells of brown pelicans showed that DDE residues correlate better with shell thinning than do residues of dieldrin or PCBs, confirming observations with cormorants and white pelicans.

Book chapter↗