Physician Specialty and Office Visits Made by Adults With Diagnosed Multiple Chronic Conditions: United States, 2014-2015.

OBJECTIVES: Adults with multiple chronic conditions (MCCs; ≥2 chronic conditions) account for a substantial number of visits to health care providers. The complexity of a patient's care, including the number of chronic conditions, may differ by physician specialty. The objectives of this study were to (1) examine differences in physician office visits among adults with MCCs by physician specialty and (2) identify the types of MCC dyads (combinations of 2 chronic conditions) most common among visits to office-based physicians. METHODS: We used data from the 2014-2015 National Ambulatory Medical Care Survey (unweighted analytic sample, n = 61 682), a nationally representative survey of physician office-based ambulatory visits, to examine differences in physician office visits among adults with MCCs by physician specialty. We also identified the most commonly observed MCC dyads among these visits. RESULTS: During 2014-2015, 40.0% of physician office visits were made by adults with MCCs. Compared with visits for all specialties combined (40.0%), a significantly higher percentage of physician office visits among adults with MCCs were to specialists in cardiovascular disease (74.7%) and internal medicine (57.6%). For all physician specialties except psychiatry, the MCC dyads of hyperlipidemia and hypertension and diabetes and hypertension were among the most commonly observed MCC dyads among visits made by adults with MCCs. CONCLUSIONS: Awareness of these findings may help specialists improve care for adults with MCCs. The recognition among physicians of common MCC dyads is relevant to the care management of persons with MCCs.

Availability of Injectable Antimicrobial Drugs for Gonorrhea and Syphilis, United States, 2016.

We estimated the availability of the injectable antimicrobial drugs recommended for point-of-care treatment of gonorrhea and syphilis among US physicians who evaluated patients with sexually transmitted infections in 2016. Most physicians did not have these drugs available on-site. Further research is needed to determine the reasons for the unavailability of these drugs.

Mental Health-related Physician Office Visits by Adults Aged 18 and Over: United States, 2012-2014.

In 2016, mental illness affected about 45 million U.S. adults (1). Although mental health-related office visits are often made to psychiatrists (2), primary care physicians can serve as the main source of treatment for patients with mental health issues (3); however, availability of provider type may vary by geographic region (3,4). This report uses data from the 2012-2014 National Ambulatory Medical Care Survey (NAMCS) to examine adult mental healthrelated physician office visits by specialty and selected patient characteristics.

The ecotoxicological recovery of Ely Creek and tributaries (Lee County, VA) after remediation of acid mine drainage.

The Ely Creek watershed (Lee County, VA) was determined in 1995 to be the most negatively affected by acid mine drainage (AMD) within the Virginia coalfield. This determination led the US Army Corps of Engineers to design and build passive wetland remediation systems at two major AMD seeps affecting Ely Creek. This study was undertaken to determine if ecological recovery had occurred in Ely Creek. The results indicate that remediation had a positive effect on all monitoring sites downstream of the remediated AMD seeps. At the site most impacted by AMD, mean pH was 2.93 prior to remediation and improved to 7.14 in 2004. Benthic macroinvertebrate surveys revealed that one AMD influenced site had increased taxa richness from zero taxa in 1997 to 24 in 2004. While in situ testing of Asian clams resulted in zero survival at five of seven AMD influenced sites prior to remediation, some clams survived at all sites after. Clam survival was found to be significantly less than upstream references at only two sites, both downstream of un-mitigated AMD seeps in 2004. An ecotoxicological rating (ETR) system that combined ten biotic and abiotic parameters was developed as an indicator of the ecological status for each study site. A comparison of ETRs from before and after remediation demonstrated that all sites downstream of the remediation had experienced some level of recovery. Although the remediation has improved the ecological health of Ely Creek, un-mitigated AMD discharges are still negatively impacting the watershed.

Nurse practitioners, certified nurse midwives, and physician assistants in physician offices.

The expansion of health insurance coverage through health care reform, along with the aging of the population, are expected to strain the capacity for providing health care. Projections of the future physician workforce predict declines in the supply of physicians and decreasing physician work hours for primary care. An expansion of care delivered by nurse practitioners (NPs), certified nurse midwives (CNMs), and physician assistants (PAs) is often cited as a solution to the predicted surge in demand for health care services and calls for an examination of current reliance on these providers. Using a nationally based physician survey, we have described the employment of NPs, CNMs, and PAs among office-based physicians by selected physician and practice characteristics.

National Ambulatory Medical Care Survey: 2007 summary.

OBJECTIVES: This report describes ambulatory care visits made to physician offices in the United States. Statistics are presented on selected characteristics of the physician's practice, the patient, and the visit. METHODS: The data presented in this report were collected in the 2007 National Ambulatory Medical Care Survey (NAMCS), a national probability sample survey of visits to nonfederal office-based physicians in the United States. Sample data are weighted to produce annual national estimates of physician visits. RESULTS: During 2007, an estimated 994.3 million visits were made to physician offices in the United States, an overall rate of 335.6 visits per 100 persons. About one-third of office visits, 34.9 percent, were made to practices with all or partial electronic medical records systems, while 85.1 percent of the visits were made to practices with all or partial electronic submission of claims. From 1997 to 2007, the percentage of visits to physicians who were solo practitioners decreased 21 percent. During the same period, visits to physicians who were part of a group practice with 6-10 physicians increased 46 percent. There were an estimated 106.5 million injury- or poisoning-related office visits in 2007, representing 10.7 percent of all visits. Medications were ordered, supplied, or administered at 727.7 million office visits, accounting for 73.2 percent of all office visits. In 2007, about 2.3 billion drugs were ordered, supplied, or administered, resulting in an average of 226.3 drug mentions per 100 visits.

Population aging and the use of office-based physician services.

KEY FINDINGS: From 1998 to 2008, the proportion of physician office-based visits in the United States became increasingly concentrated on those aged 45 and over. The intensity of physician office visits, as measured by medications prescribed or continued, imaging tests ordered or provided, and time spent with physicians, also became increasingly concentrated on those aged 45 and over. Although most physicians accept Medicare patients, acceptance of Medicare was higher among ophthalmologists and general surgeons than among general or family practitioners, internists, and psychiatrists. Over the past 30 years, the specialty concentration of visits has shifted significantly. In 1978, 62 percent of visits by patients aged 65 and over were to primary care physicians compared with 45 percent in 2008. The percentage of visits to physicians with a medical or surgical specialty increased from 37 percent to 55 percent.

Preliminary results of laboratory toxicity tests with the mayfly, Isonychia bicolor (Ephemeroptera: Isonychiidae) for development as a standard test organism for evaluating streams in the Appalachian coalfields of Virginia and West Virginia.

Selecting the most appropriate test species for sediment and water column assays has been a primary goal for ecotoxicologists. Standard test organisms and established test guidelines exist, but the USEPA-recommended species may not be the most sensitive organisms to anthropogenic inputs. This paper describes preliminary results of toxicity tests with the mayfly, Isonychia bicolor (Ephemeroptera). Results suggested that Isonychia were moderately sensitive to NaCl after 96 h with an average LC(50) value of 3.10 g NaCl per liter. This value decreased after 7 days of exposure, resulting in a mean LC(50) value of 1.73 g NaCl per liter. When exposed to a coal-mine-processed effluent, Isonychia generated LC(50) values that ranged from 13% to 39% effluent. I. bicolor were more sensitive to the coal processing effluent than Ceriodaphnia dubia with conductivity lowest observable effects concentration (LOEC) values for mayfly survivorship that ranged from 1,508 to 4,101 microS/cm, while LOEC values for C. dubia reproduction ranged from 2,132 to 4,240 microS/cm.

Racial differences in visit duration of outpatient psychiatric visits.

CONTEXT: Substantial racial disparities exist in the delivery of some health care services. Whether racial disparities exist in the duration of office visits to psychiatrists is not known. OBJECTIVE: To compare the duration of visits to office-based psychiatrists by white and African American patients. DESIGN, SETTING, AND PARTICIPANTS: Analysis of a nationally representative sample of visits to office-based psychiatrists between 2001 and 2006. Visits were grouped by patient race as non-Hispanic African American (n = 504) or non-Hispanic white (n = 7094). Main Outcome Measure Duration of face-to-face contact between patient and psychiatrist. RESULTS: Unadjusted mean duration of psychiatric outpatient visits by African Americans (mean duration, 28.3 minutes) were 4.4 minutes shorter than visits by whites (32.7 minutes) (P = .02), although the difference narrowed (3.5 minutes; P = .07) following adjustment for potentially confounding patient, psychiatrist, and practice characteristics. A gap was evident in 2001-2003 (7.4 minutes; P <.001) but negligible in 2004-2006 (0.1 minute; P = .94). In stratified regressions that combined time periods and controlled for several relevant characteristics, significant racial differences in visit duration were observed among visits with the following characteristics: adjustment disorder diagnosis (10.0 minutes; P <.001), female patient sex (5.4 minutes; P = .008), depressive disorder diagnosis (5.2 minutes; P = .04), solo practice (5.2 minutes; P = .04), psychotherapy provision (5.1 minutes; P = .01), practices with high patient volume (5.0 minutes; P = .03), Medicare payment (3.5 minutes; P = .02), and absence of psychiatric comorbidity (3.3 minutes; P = .04). CONCLUSIONS: In recent years, progress has been made in closing a racial gap in the length of psychiatric office-based outpatient visits by African American vs white patients. Against a backdrop of persisting racial disparities in other areas of mental health care, ongoing attention to reducing disparities will be necessary to sustain and extend these gains.

National Ambulatory Medical Care Survey: 2006 summary.

OBJECTIVES: This report describes ambulatory care visits made to physician offices in the United States. Statistics are presented on selected characteristics of the physician's practice, the patient, and the visit. METHODS: The data presented in this report were collected in the 2006 National Ambulatory Medical Care Survey (NAMCS), a national probability sample survey of visits to nonfederal office-based physicians in the United States. Sample data are weighted to produce annual national estimates of physician visits. RESULTS: During 2006, an estimated 902 million visits were made to physician offices in the United States, an overall rate of 306.6 visits per 100 persons. In over one-quarter of office visits, electronic medical records were utilized by physicians, while at 85.5 percent of visits, claims were submitted electronically. Since 1996, the percentage of visits by adults 18 years and over with chronic diabetes increased 40%, and during the same time period, visits increased for chronic hypertension (28%), and depression (27%). Among visits by females, a Pap test was ordered or provided more frequently than a human papilloma virus DNA test (5.6 versus 0.6 percent). Private insurance visits were more likely to include liquid-based Pap tests (6.3 percent) compared with visits using conventional or unspecified tests (3.7 percent), whereas visits utilizing Medicaid and other sources of payment were equally likely to provide conventional or unspecified, and liquid-based Pap tests. Medication therapy was reported at 636.7 million office visits, accounting for 70.6 percent of all office visits. In 2006, there were about 1.9 billion drugs mentioned, resulting in an overall 210.3 drug mentions per 100 visits. Visits to primary care physicians at community health centers were more likely to document health education compared with office-based practices, whereas diagnostic or screening services, drug mentions, and any nonmedication treatment occurred at approximately the same proportion of visits for primary care providers in both type of settings.

National Ambulatory Medical Care Survey: 2005 summary.

OBJECTIVES: This report describes ambulatory care visits made to physician offices in the United States. Statistics are presented on selected characteristics of the physician's practice, the patient, and the visit. METHODS: The data presented in this report were collected in the 2005 National Ambulatory Medical Care Survey (NAMCS), a national probability sample survey of visits to nonfederal office-based physicians in the United States. Sample data are weighted to produce annual national estimates of doctor visits. RESULTS: During 2005, an estimated 963.6 million visits were made to physician offices in the United States, an overall rate of 331.0 visits per 100 persons. In one-quarter of office visits, electronic medical records were utilized by physicians, while at 83.9 percent of visits, claims were submitted electronically. As the baby boomer generation aged, there was a shift in utilization, as the majority of visits in 1995 were by patients 25-44 years of age compared with 2005, when most visits were by patients 45-64 years of age. In 2005, 52.7 percent of office visits were made by patients with at least one chronic condition. Hypertension was the most frequent condition (22.8 percent), followed by arthritis (14.3 percent), hyperlipidemia (13.5 percent), and diabetes (9.8 percent). Medication therapy was reported at 679.2 million office visits, accounting for 70.5 percent of all office visits. In 2005, there were about 2.0 billion drugs prescribed, resulting in an overall rate of 210.7 drugs per 100 visits. Drugs with amoxicillin were more likely to be new prescriptions (85.4 percent), while ibuprofen and acetaminophen were just as likely to be a new or continued drug. The overall mean time spent with a physician, excluding psychiatrists, has not changed since 1995; however, visits with a duration of 6-10 minutes decreased by 28% from 1995, while visits lasting 16-30 minutes increased by 20%.

Coal-mine hollow fill and settling pond influences on headwater streams in southern West Virginia, USA.

The influences of coal-mine hollow fills and associated settling ponds in three headwater streams were assessed in southern West Virginia, USA. Fill drainage waters had elevated conductivities and metal concentrations, compared to a regional reference. Benthic macroinvertebrate richness was not affected consistently by the hollow fill drainages, relative to a regional reference, although a more tolerant community, lacking in Ephemeroptera taxa at most locations, was evident. Collector-filterer populations were elevated at monitoring stations directly below the settling ponds, indicating that the ponds' presence influenced macroinvertebrate community structure by means of organic enrichment. Corbicula fluminea growth was enhanced in monitoring locations directly below the settling ponds, also an apparent result of organic enrichment. Results of acute water column toxicity testing with Ceriodaphnia dubia, sediment chronic toxicity testing with Daphnia magna, and in-situ ecotoxicological assessments with C. fluminea demonstrated no mortality or toxic influence at most of the sites tested below the ponds. The settling ponds appear to serve as sinks in collecting some, but not all, trace metals.

Chlorine toxicity to early life stages of freshwater mussels (Bivalvia: Unionidae).

Chlorine (Cl) is a highly toxic, widely used halogen disinfectant that is present in point-source pollution discharges from wastewater treatment plants and industrial facilities. The U.S. Environmental Protection Agency freshwater criteria for Cl are 19 microg total residual Cl (TRC)/L as a maximum 1-h average concentration and 11 microg TRC/L as a maximum 4-d average; however, toxicological data for unionids were not used in these calculations. To address this void in the data, we conducted acute tests with glochidia from several species and 21-d bioassays with three-month-old Epioblasma capsaeformis and three-, six-, and 12-month-old Villosa iris juveniles. The 24-h lethal concentration 50 values for glochidia were between 70 and 220 [Lg TRC/L, which are 2.5 to 37 times higher than those reported in other studies for cladocerans. Significant declines in growth and survivorship were observed in the 21-d test with E. capsaeformis at 20 microg TRC/L. Lowest-observed-adverse-effects concentrations in bioassays with juvenile V. iris were higher (30-60 microg TRC/L) but showed a significant trend of declining toxicity with increased age. Although endpoints were above water quality criteria, the long life spans of unionids and potential implications of chronic exposure to endangered juvenile mussels still warrant concern.

National Ambulatory Medical Care Survey: 2004 summary.

OBJECTIVES: This report describes ambulatory care visits made to physician offices in the United States. Statistics are presented on selected characteristics of the physician's practice, the patient, and the visit. Selected trends in office visits are also presented. METHODS: The data presented in this report were collected in the 2004 National Ambulatory Medical Care Survey (NAMCS), a national probability sample survey of visits to office-based physicians in the United States. Sample data are weighted to produce annual national estimates using an estimator that uses a revised nonresponse adjustment. RESULTS: During 2004, an estimated 910.9 million visits were made to physician offices in the United States, an overall rate of 315.9 visits per 100 persons. Overall, 58.9 percent of visits were to physicians in the specialties of general and family practice, internal medicine, pediatrics, and obstetrics and gynecology. In 2004, primary care specialists provided 87.2 percent of all preventive care visits. The percentage of visits relying on Medicaid or the State Children's Health Insurance Program increased by 36% between 2001 and 2004. Essential hypertension, malignant neoplasms, acute upper respiratory infection, and diabetes mellitus were the leading illness-related primary diagnoses. There were an estimated 105.3 million injury-related visits in 2004, or 36.5 visits per 100 persons. Diagnostic or screening services were ordered or provided at 85.9 percent of visits, and counseling, education, therapeutic, or preventative services were ordered or provided at 42.0 percent of visits. Medications were prescribed or provided at 64.2 percent of visits.

The ecotoxicological recovery of Ely Creek and tributaries (Lee County, VA) after remediation of acid mine drainage.

The Ely Creek watershed (Lee County, VA) was determined in 1995 to be the most negatively affected by acid mine drainage (AMD) within the Virginia coalfield. This determination led the US Army Corps of Engineers to design and build passive wetland remediation systems at two major AMD seeps affecting Ely Creek. This study was undertaken to determine if ecological recovery had occurred in Ely Creek. The results indicate that remediation had a positive effect on all monitoring sites downstream of the remediated AMD seeps. At the site most impacted by AMD, mean pH was 2.93 prior to remediation and improved to 7.14 in 2004. Benthic macroinvertebrate surveys revealed that one AMD influenced site had increased taxa richness from zero taxa in 1997 to 24 in 2004. While in situ testing of Asian clams resulted in zero survival at five of seven AMD influenced sites prior to remediation, some clams survived at all sites after. Clam survival was found to be significantly less than upstream references at only two sites, both downstream of un-mitigated AMD seeps in 2004. An ecotoxicological rating (ETR) system that combined ten biotic and abiotic parameters was developed as an indicator of the ecological status for each study site. A comparison of ETRs from before and after remediation demonstrated that all sites downstream of the remediation had experienced some level of recovery. Although the remediation has improved the ecological health of Ely Creek, un-mitigated AMD discharges are still negatively impacting the watershed.

Bioassessment of an Appalachian headwater stream influenced by an abandoned arsenic mine.

Recent debate concerning the modification of safe drinking water standards for arsenic (As) has led to increased awareness of the risks As poses to both humans and the environment. However, few studies have examined the effects of As on the diversity and composition of aquatic assemblages in streams. Benthic macroinvertebrate surveys, chemical analysis of water column and sediment, and laboratory toxicity tests were conducted to assess effects of an abandoned As mine on a headwater stream, and to determine the primary component of toxicity. The average 48-hr LC50 value for Daphnia magna was 4316 microg As/L, and the average 96-hr LC50 value for Lepidostoma spp. was 2138 microg As/L. Reproduction was significantly reduced for D. magna at concentrations > or =312 microg As/L in water column laboratory bioassays, and for treatments in bioassays with sediments containing elevated As (> or =2630 mg/kg). These results support the findings of the in-stream benthic macroinvertebrate survey as the density and percent Ephemeroptera + Plecoptera, + Trichoptera (EPT) were substantially lower at sites downstream of the mine compared to upstream reference sites. Results of bioassays comparing the toxicity of As-contaminated site water and upstream reference water spiked with As salts suggest that As is the primary component of toxicity impacting the stream. Measured As concentrations at downstream sites were above the recommended Criterion Maximum Concentration of 340 microg As/L and Criterion Continuous Concentration of 150 microg As/L for protection of aquatic life published by the United States Environmental Protection Agency. At the study site, elevated As concentrations likely prevent recruitment of benthic macroinvertebrates and recovery of the perturbed headwater stream.

Acute and chronic toxicity of mercury to early life stages of the rainbow mussel, Villosa iris (Bivalvia: Unionidae).

Mercury (Hg) contamination is receiving increased attention globally because of human health and environmental concerns. Few laboratory studies have examined the toxicity of Hg on early life stages of freshwater mussels, despite evidence that glochidia and juvenile life stages are more sensitive to contaminants than adults. Three bioassays (72-h acute glochidia, 96-h acute juvenile, and 21-d chronic juvenile toxicity tests) were conducted by exposing Villosa iris to mercuric chloride salt (HgCl2). Glochidia were more sensitive to acute exposure than were juvenile mussels, as 24-, 48-, and 72-h median lethal concentration values (LC50) for glochidia were >107, 39, and 14 microg Hg/L, respectively. The 24-, 48-, 72-, and 96-h values for juveniles were 162, 135, 114, and 99 microg Hg/L, respectively. In the chronic test, juveniles exposed to Hg treatments > or = 8 microg/L grew significantly less than did control organisms. The substantial difference in juvenile test endpoints emphasizes the importance of assessing chronic exposure and sublethal effects. Overall, our study supports the use of glochidia as a surrogate life stage for juveniles in acute toxicity tests. However, as glochidia may be used only in short-term tests, it is imperative that an integrated approach be taken when assessing risk to freshwater mussels, as their unique life history is atypical of standard test organisms. Therefore, we strongly advocate the use of both glochidia and juvenile life stages for risk assessment.

Freshwater mussel shells as environmental chronicles: geochemical and taphonomic signatures of mercury-related extirpations in the North Fork Holston River, Virginia.

This study utilized freshwater mussel shells to assess mercury (Hg) contamination in the North Fork Holston River that extirpated (caused local extinctions of) a diverse mussel fauna. Shells (n = 366) were collected from five sites situated upstream (two sites), just below (one site), and downstream (two sites) of the town of Saltville, Virginia, where Hg was used to produce chlorine and caustic soda from 1950 to 1972. Shell samples were used to test the (1) utility of geochemical signatures of shells for assessing the spatial variation in Hg levels in the river relative to the contamination source and (2) value of taphonomy (post-mortem shell alteration) for distinguishing sites that differ in extirpation histories. Geochemical signatures of 40 shells, analyzed using atomic absorption spectroscopy, indicated a strong longitudinal pattern. All shells from the two upstream sites had low Hg concentrations (<5-31 microg/kg), shells directly below Saltville had variable, but dramatically higher concentrations (23-4637 microg/kg), and shells from the two downstream sites displayed intermediate Hg levels (<5-115 microg/kg) that declined with distance from Saltville. Two pre-industrial shells, collected at Saltville in 1917, yielded very low Hg estimates (5-6 microg/kg). Hg signatures were consistent among mussel species, suggesting that Hg concentrations were invariant to species type; most likely, highly variable Hg levels, both across sites and through time, overwhelmed any interspecific differences in Hg acquisition. Also, a notable postmortem incorporation of Hg in mussel shells seemed unlikely, as the Hg content was not correlated with shell taphonomy (r= 0.18; p = 0.28). The taphonomic analysis (n = 366) showed that the degree of shell alteration reliably distinguished sites with different extirpation histories. At Saltville, where live mussels have been absent for at least 30 years, shells were most heavily altered and fragmented. Conversely, fresh-looking shells abounded upstream, where reproducing mussel populations are still present. In summary, relic shells offered valuable spatio-temporal data on Hg concentrations in a polluted ecosystem, and shell taphonomic signatures discriminated sites with different extirpation histories. The shell-based strategies exemplified here do not require sampling live specimens and may augment more standard strategies applied to environmental monitoring. The approach should prove especially useful in areas with unknown extirpation and pollution histories.

National Ambulatory Medical Care Survey: 2002 summary.

OBJECTIVE: This report describes ambulatory care visits made to physician offices in the United States. Statistics are presented on selected characteristics of the physician's practice, the patient, and the visit. This report also highlights visits to primary care specialties. METHODS: The data presented in this report were collected from the 2002 National Ambulatory Medical Care Survey (NAMCS). NAMCS is a part of the ambulatory care component of the National Health Care Survey that measures health care utilization across various types of providers. NAMCS is a national probability sample survey of visits to office-based physicians in the United States. Sample data are weighted to produce annual national estimates. Selected trends from 1992, 1993, 1995, and 1997 are also presented. RESULTS: During 2002, an estimated 890 million visits were made to physician offices in the United States, an overall rate of 314.4 visits per 100 persons. From 1992 through 2002, the visit rate for persons 45 years of age and over increased by 14%, from 407.3 to 465.8 visits per 100 persons. The visit rate to physician offices in metropolitan statistical areas (MSAs) (337.3 visits per 100 persons) was significantly larger than the rate in non-MSAs (221.9 visits per 100 persons). For one-half of all office visits, regardless of specialty, physicians indicated they were the patient's primary care physician (PCP). Of the visits to physicians other than the patient's PCP, about one-third (31.1 percent) were referrals. New patients, representing 12.1 percent of the visits in 2002, are down 18% since 1992. Primary care specialists provided 90 percent of all preventive care visits. Essential hypertension, acute upper respiratory infection, diabetes mellitus, and arthropathies were the leading illness-related primary diagnoses. There were an estimated 104.0 million injury-related visits in 2002, or 36.7 visits per 100 persons. On average, 2.3 medications were ordered or provided at each office visit with any mention of a medication. The leading therapeutic class for drugs mentioned at office visits included nonsteroidal anti-inflammatory drugs (NSAIDs) (4.9 mentions per 100 visits) and antidepressants (4.5 mentions per 100 visits). Of primary care specialists, 25.8 percent reported not accepting new patients who are Medicaid enrollees.

Effect of cage design on growth of transplanted Asian clams: implications for assessing bivalve responses in streams.

This study was designed to determine whether survivorship and growth of Asian clams (Corbicula fluminea [Müller]) differed significantly between two types of field enclosures. Enclosures were either flexible mesh bags or rigid cages (hereto after referred as bioboxes) designed to homogenize substrate among study sites and accommodate Asian clam feeding mechanisms. For 96d, cages remained at 12 Clinch River (CR), Hurricane Fork (HF), and Dump's Creek (DC) sites upstream and downstream of a coal-fired power plant discharge, coal mining effluent, and coal combustion-related disposal facilities in Carbo, Virginia. Although survivorship was not significantly different between cage types, mean growth of clams in bioboxes was significantly greater overall (p = 0.0157). Despite the difference in growth between the two cage types, both confirmed significant reductions of survivorship and growth directly below the power plant discharge. Additionally, coefficient of variance values for biobox growth data were reduced at most study sites (averages of 16% for bioboxes versus 19% for mesh bags). Our results have implications toward strengthening weight-of-evidence approaches used to link impairment of transplanted bivalves to environmental contaminants. More importantly, these results suggest that ecotoxicological impairment of bivalves transplanted downstream of the coal-fired power plant discharge functioned independently of site-specific substrate provisions.