Effects of herbicides on streamAufwuchs productivity and nutrient uptake

The effects of atrazine and a combination of alachlor, atrazine, metolachlor, and metribuzin on the productivity and nutrient uptake rates of native streamAufwuchs communities were investigated in two separate artificial stream experiments. After an 8-day colonization period, the first experiment employed constant doses of atrazine at 0 g/L (control), 24 g/L and 134 g/L. The second experiment employed a pulsed dose having maximum concentrations of 35 g/L alachlor, 109 g/L atrazine, 90 g/L metolachlor, and 21 g/L metribuzin. Each 20-day experiment was run at both 10C and 25C. Constant exposure to 24 g/L atrazine yielded a significant reduction in both ash-free dry weight (AFDW) and chlorophylla at 25C but not at 10C. Constant exposure to 134 g/L atrazine yielded significantly less AFDW and chlorophylla at both temperatures. The pulsed exposure to four herbicides yielded significantly less AFDW at both temperatures, while chlorophylla was significantly less only at 10C. During continual exposure to 134 g/L atrazine, both NO₂ + NO₃ and silica uptake rates appeared to be reduced at both temperatures, although the differences were generally not statistically significant. At 10C uptake rates of soluble reactive phosphorus and NO₂ + NO₃ were depressed temporarily by exposure to the pulse of four herbicides, recovering to control rates within a few days, while no effect on uptake rates was discerned at 25C. The temperature difference between experimental runs had a greater effect on nutrient uptake rates than did the herbicide treatments during a run. The results indicate thatAufwuchs growth and nutrient uptake rates may be reduced temporarily by herbicide exposures in agricultural streams. However, greater effects on these processes may be exerted by other factors accompanying storm events, such as reduced temperatures.     

Stabilization of alanine aminopeptidase,gamma glutamyltranspeptidase,and N-acetyl-Β-D-glucosaminidase activity in normal urines

The question of assessing renal toxicity in studies of humans exposed to environmental toxicants is of major concern in health effects studies. The measurement of urinary enzymes is a reliable, sensitive indicator of renal tubular damage due to a variety of causes, including heavy metal and drug toxicity. However, urine is not a favorable matrix for some enzymatic activities because certain enzymes are less stabile in urine than in a matrix such as serum. This study addresses the problem of the lack of stability of alanine aminopeptidase (AAP) and gamma glutamyltranspeptidase (GGT) in the urinary matrix. Four urinary treatment methods consisting of dialysis or the addition of albumin, dimethyl sulfoxide, or glycerol have been examined and compared. The activities of AAP, GGT, andN-acetyl--D-glucosaminidase (NAGA) in six normal treated and untreated urines were followed for 28 days at 4C and for 6 months at –20C. This study indicates that of the methods tested, giycerol treatment provides the most stable AAP and GGT activity and is the most reliable method for stabilizing these enzymes in frozen urine. Even with giycerol treatment, some GGT activity is lost (mean loss of 11% over 6 months at –20C), indicating GGT should be assayed as soon as possible. NAGA activity is most stable in untreated urines but still increases by approximately 9% (mean of six samples) in 6 months at –20C. The implications of observed effects of dialyzable inhibitors are discussed for the three enzymes.     

Ergonomische Gestaltung von alphanumerischen Tastaturen

Summary Split keyboards have been developed based on laboratory and field studies. They are characterized by a large forearm/hand support, an angle between the two half keyboards of 25, a frontal-, lateral inclination of 10 and a hand-conforme key arrangement. These split keyboards reduce constrained postures in arms and hands. The keyboard can be operated with supported forearms. Work on a split keyboard is more comfortable and it was preferred by a large majority of the users.

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Forme ergonomique de claviers alphanumériques

Résumé Sur la base d'expériences en laboratoire et sur le terrain on a développé des demi-claviers ergonomiques. Ceux-ci sont caractérisés par un grand support pour les avant-bras et les mains. Les deux demi-claviers présentent un angle d'ouverture de 25, une inclinaison frontale et latérale de 10, et une adaptation des touches à la forme des mains. Les demi-claviers réduisent la posture de contrainte des bras et des mains, du fait que les touches peuvent Être utilisées avec les avant-bras appuyés. Le travail sur ces nouveaux demi-claviers diminue les douleurs et est plus facilement accepté par les employés.

     

Thermal effects on the accumulation of arsenic in green sunfish,Lepomis Cyanellus

The pattern of arsenic concentration in several tissues ofLepomis cyanellus was measured (by neutron activation analysis) as a function of exposure time at 10, 20, and 30C and 0, 30, 60 ppm of arsenic as sodium arsenate. Individual variability of arsenic uptake did not override trends of greater uptake with increasing exposure time, temperature, and arsenic concentration. The mean temperature coefficient of 4.5 for arsenic uptake in livers was higher than O'Hara's (1968) metabolic figures of 1.6 to 3.0 forLepomis species. The biological half-life of arsenic in liver and gut of live specimens exposed to 30 and 60 ppm of arsenic at 10C was about one week. Percentage survival decreased and mean arsenic uptake increased slightly as temperature and arsenic concentration increased.     

Recherche et Dosage de l'Aminocarb dans les Eaux Naturelles et le Feuillage du Sapin Baumier par Chromatographie en Phase Gazeuse

Summary Aminocarb (4-dimethylamino-m-tolyl methylcarbamate), a carbamate insecticide, is now widely used for the control of spruce budworm (Choristoneura fumiferana) in Quebec forest spray programs. This paper describes a method for the determination of residues of this insecticide in natural waters and balsam fir foliage.The insecticide was extracted from water with chloroform and from foliage with ethyl acetate. The extracts were purified by coagulation with an aqueous solution of ammonium chloride and phosphoric acid. The acidified aqueous solution containing the insecticide was partitioned with methylene chloride, neutralized with sodium carbonate and then extracted with chloroform. The organic extract was concentrated to an appropriate volume and injected directly into a gas Chromatograph (GLC) equipped with dual nitrogen phosphorous detector (NPD). Oven and injector temperatures were reduced, and maintained respectively at 130C and 150C. Glass Columns, 60 cm × 2 mm (I.D.), in GLC were packed with a mixture of 4% OV-101 + 6% OV-210 on Gas Chrom Q (80–100 mesh), and 3% OV-17 on the same support for confirmatory analysis.Under the conditions used, aminocarb were successfully chromatographed on both columns without decomposition. Average aminocarb recoveries of more than 90% from foliage and nearly 100% from water were obtained at fortification levels of 1 g/g and 1 g/l respectively. Clean up efficiency made possible a detection limit ranging from 0.002 to 0.005 g/g for foliage. The detection limit for water was 0.01 g/l.     

Toxicity of natural pyrethrins and five pyrethroids to fish

The toxicity of natural pyrethrins and five pyrethroids was determined with coho salmon (Oncorhynchus kisutch), steelhead trout (Salmo gairdneri), fathead minnow (Pimephales promelas), channel catfish (Ictalurus punctatus), bluegill (Lepomis macrochirus), and yellow perch (Perca flavescens). The 96-hour LC₅₀'s in static tests at 12C ranged from 24.6 to 114g/1 of natural pyrethrins and from 0.110 to 1,140g/1 of pyrethroids. Two pyrethroids, RU-11679 and SBP-1382^(R), were over 10 times more toxic than pyrethrum extract in the flow-through tests. Coldwater species of fish were more sensitive than warmwater species to all the compounds. Temperature (12–22C) influences the toxicity of natural pyrethrin and the pyrethroids. The natural pyrethrin was more toxic to fish in pH 6.5 than in pH 9.5 water, but the toxicity of pyrethroids was not influenced in that pH range. The two most toxic pyrethroids, RU-11679 and SBP-1382, were deactivated more rapidly in water solutions than natural pyrethrins, S-bioallethrin, dimethrin, andd-trans allethrin.     

Aufbau und Funktion einer Klimaanlage für klinische Untersuchungen zur Prüfung klimatischer Einflüsse auf die Atmung

Zusammenfassung Aufbau und Funktion einer Klimaanlage zur Prüfung der Wirkung klimatischer Einflüsse auf Atmung und Kreislauf werden beschrieben. Es handelt sich um eine 4-Zimmeranlage, in der insgesamt 8 Patienten bzw. Probanden auch für Langzeitversuche untergebracht werden können. Die erreichbaren Temperaturen liegen zwischen 5 und 35 C, bei relativen Feuchten zwischen 5 und 98% r. F. Die Gesamtanlage wird im Frischluft-Umluftbetrieb nach einem modernen Prinzip der indirekten Soletemperierung mit Verdunstungsbefeuchtung klimatisiert. Die Anlage gibt außerdem die Möglichkeit, im reinen Frischluftbetrieb Patienten bzw. Probanden einer mit Staub oder Sohadgas beladenen Luft in den angegebenen Temperatur- und Feuchtebereichen auszusetzen. Es wird über erste Erfahrungen und Ergebnisse nach einjährigem Betrieb der Anlage berichtet.

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Construction and functioning of an air-conditioning plant to study the effect of climatic influences on respiration

Summary Construction and functioning of an air-conditioning plant installed to study the effect of climatic influences on respiration and circulation are described. The design consists of 4 rooms, where 8 patients can be hospitalized, also for long-term experiments. The attainable temperatures are between 5 C and 35 C at relative humidities between 5 and 98 per cent. The whole plant is air-conditioned by means of a partly system which circulates fresh air and partly recirculates used air, designed according to modern principles of indirect rated temperatures with evaporative moistening. It is also possible to expose patients, while living in pure fresh-air, to air contaminated with dust or a noxious gas within the temperature and humidity ranges given above. The experiences and results of the first year of operation are reported.

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Die Anlage wurde mit Hilfe des Verein zur Untersuchung von Einwirkungen der Luftverschmutzung auf die Volksgesundheit e.V. Bochum erstellt. Ausführung der Gesamtanlage: Firma Karl Weiss, 6301 Lindenstruth (Krs. Gießen).     

Histopathological progression of hemic neoplasms in the tropical crab Paratelphusa hydrodromous (Herbst) treated with sublethal cadmium chloride

Tropical crab Paratelphusa hydrodromous were exposed in the laboratory to five sublethal cadmium chloride concentrations (0.02, 0.05, 0.25 and 0.50M/L) for 30 days to evaluate the cellular inflammatory and chronic pathologic responses. The most frequent pathologic responses of hepatopancreas exposed to 0.25–0.50 M CdCl₂/L were atrophy of R-cells and the development of granulomatous reaction consisting of granulocytes and monomorphic basophilic cells. Coagulative necrosis was evident in the young oocytes at 0.05 M CdCl₂/L which was accompanied by the increased vitellophagia of follicle cells. Thirty-day exposure to 0.25–0.50 M CdCl₂/L shortened the reproductive life span of the crabs by inducing spontaneous atresia and granulocytosis. Eosinophilic granulocytes, the most numerous cell type found in the necrotic centers, phagocytosed the masses of cellular debris and yolk from cadmium-induced atretic oocytes. The widespread proliferation of basophilic cells related to hyalinocyte with high nucleocytoplasmic ratio would suggest the development of hemic neoplasia. Heavy granulocytic infiltration was the typical cellular inflammatory response during chronic pathological conditions.     

Identification of PCB's in the presence of DDT-type compounds using low temperature luminescence

Low temperature (77K) luminescence spectra of polychlorinated biphenyls (PCB's), DDT-type compounds and mixtures suggest a simplified method for identification and quantitation of aromatic pesticides with minimal prior sample treatment. Spectral differences allow identification of PCB's in the presence of DDT and the converse. Approximate detection limits, possible interferences and suggestions for further work are discussed.Presented at the Third International Congress of Pesticide Chemistry (IUPAC), Helsinki, Finland, 1974.     

Bromacil and diuron herbicides: Toxicity,uptake, and elimination in freshwater fish

Fathead minnows, 30 days old, were exposed to technical grade bromacil and diuron in flow-through tests to determine acute toxicity. LC₅₀ values for bromacil were 185, 183, 182 and 167 mg/L at 24, 48, 96, and 168 hr, respectively; and for diuron, 23.3, 19.9, 14.2, and 7.7 mg/L at 24, 48, 96, and 192 hr, respectively. Eggs, newly hatched fry, and juvenile fish were continuously exposed to lower concentrations of the herbicides for 64 days. Growth was significantly reduced (p 0.01) at the lowest bromacil exposure of 1.0 mg/L. Therefore, it was not possible to determine a no effect concentration. The no effect concentration for diuron was 33.4 g/L, while the lowest concentration which resulted in adverse effects was 78.0 g/L. Adverse effects at 78.0 g/L were an increased incidence of abnormal or dead fry immediately after hatch (p 0.01) and decreased survival throughout the exposure period (p 0.05). Neither herbicide accumulated significantly in fish tissue, as bioconcentration factors were <3.2 and 2.0 for bromacil and diuron, respectively. Rainbow trout (Salmo gairdneri) injected with radiolabeled bromacil or diuron eliminated over 90% of the radioactivity within 24 hr. Parent compound and metabolites were detected in the aquarium water in both cases. Metabolites of diuron recovered from the water included 3,4-dichloroaniline and several demethylated products.     

Toxicity of mercury,copper, nickel,lead, and cobalt to embryos and larvae of zebrafish,Brachydanio rerio

The toxicity of mercury (HgCl₂), copper (CuCl₂: 5 H₂O), nickel (NiSO₄: 6 H₂O), lead (Pb(CH₃COO)₂: 3 H₂O) and cobalt (CoCl₂: 6 H₂O) was studied under standardized conditions in embryos and larvae of the zebrafish,Brachydanio rerio. Exposures were started at the blastula stage (2–4 h after spawning) and the effects on hatching and survival were monitored daily for 16 days. Copper and nickel were more specific inhibitors of hatching than cobalt, lead, and mercury. Nominal no effect concentrations determined from the dose-response relationships (ZEPs, Zero Equivalent Points) for effect on hatching time were 0.05 g Cu/L, 10 g Hg/L, 20 g Pb/L, 40 g Ni/L and 3,840 g Co/L, and those for effect on survival time were 0.25 g Cu/L, 1.2 g Hg/L, 30 g Pb/L, 80 g Ni/L, and 60 g Co/L. The no effect concentrations for Ni, Hg and Pb are consistent with previously reported MATC values for sensitive species of fish. The no effect concentrations for copper are 1–2 orders of magnitude lower than previously reported values. The major reason for the latter discrepancy was considered to be the absence of organics that can complex copper ions in the reconstituted water that we used, which had a hardness of 100 mg/L (as CaCO₃) and a pH of 7.5–7.7. Unexposed controls were started with embryos from different parental zebrafishes and the parental-caused variability in early embryo mortality, median hatching time and median survival time were estimated.     

The influence of season and exercise on the lethal toxicity of cyanide to rainbow trout (Salmo gairdneri)

The lethal toxicity (96-hr LC₅₀) of cyanide (HCN) to juvenile rainbow trout (Salmo gairdneri) varied seasonally and with exercise (swimming at one body length/sec). The trout were acclimated to the 12C test temperature for 3–4 weeks, under a 12 hr photoperiod before being tested at different times of the year. In summer, there was no significant difference of sensitivity between exercised and non-exercised trout. From summer to winter, the 96-hr LC₅₀ for exercised trout remained unchanged at 0.052 mg/L HCN while the LC₅₀ of the non-exercised trout dropped significantly to 0.043 mg/L HCN. The median survival times of the two groups of trout were the same in the summer, but in winter the exercised fish survived twice as long as the non-exercised fish. A longer acclimation period of the non-exercised trout from 4 weeks to 10 weeks during the winter increased resistance to cyanide.     

Chronic toxicity and bioaccumulation of 2,5,2′,5′- and 3,4,3′,4′-tetrachlorobiphenyl and Aroclor® 1242 in the amphipodHyalella azteca

The addition of 100 (g/L of Aroclor^® 1242 (A1242) or 2,5,2,5-tetrachlorobiphenyl (TeCB) during 10 week chronic toxicity tests withHyalella azteca resulted in complete mortality. There were no effects on survival, growth, or reproduction after addition of 30 g/L. Toxic effects were observed at tissue levels of between 30 and 180 g/g on a wet weight basis, and tissue levels appear to be a better indicator of toxicity than levels in water. No toxic effects were observed after additions of up to 2,700 g/L of the coplanar congener 3,4,3,4-TeCB.H. azteca has the ability to avoid accumulating in excess of 140 g/g 3,4,3,4-TeCB. The amount taken up was proportional to the amount added in water up to 100 g/L, but was constant at higher additions, possibly accounting for its relatively low toxicity. The low toxicity of the coplanar congener, as compared to the non-coplanar 2,5,2,5-TeCB, is in direct contrast to the high toxicity of coplanar PCB congeners to mammals and may be associated with slower rates of aromatic hydrocarbon metabolism in amphipods. Polychlorinated biphenyl levels measured in amphipods from Lake Ontario are approximately 100-fold below levels associated with toxicity inH. azteca, but are above levels which, through biomagnification up the food chain, lead to salmonid residues in excess of 2 g/g, a tolerance limit for human consumption.     

The effect of sublethal cyanide exposure on plasma viteliogenin levels in rainbow trout (Salmo gairdneri) during early vitellogenesis

Female rainbow troutSalmo gairdneri were exposed to 0.01 mg L^–1 hydrogen cyanide (HCN) for 12 days at 12.5 ± 0.5C at the onset of vitellogenesis (May–June). Plasma vitellogenin levels were measured, utilizing a homologous radioimrnunoassay specifically developed for this species. Exposure to HCN reduced vitellogenin levels in the plasma to levels recorded in the control non-vitellogenic group. Similarly, the gonadosomatic index declined steadily throughout the experimental period in vitellogenic females exposed to cyanide while no difference was observed in hepatosomatic indices relative to controls. The high sensitivity of the radioimmunoassay for vitellogenin utilized in this study has permitted a rapid assessment of the effects of low levels of this toxicant on yolk production. The findings indicate that exposure of naturally reproducing female rainbow trout to this low concentration of HCN during early vitellogenesis would eliminate an important source of yolk precursor synthesized in the liver and sequestered by the ovary.     

Chronic effect of copper on the bluntnose minnow,Pimephales notatus (Rafinesque)

A laboratory chronic toxicity test in which bluntnose minnows were exposed to copper in laboratory dilution water with a hardness of 200 mg/L as CaCO₃ indicated that copper adversely affected fry survival, fry growth, and reproduction. The maximum acceptable toxicant concentration (MATC) for total copper based on reproductive impairment at 18.0 g/L was between 4.3 (control concentration) and 18.0 g/L.The 96-hr LC50 values from three acute toxicity tests ranged from 0.22 to 0.27 mg/L total copper with a mean value of 0.23 mg/L. The application factor (MATC/96-hr LC50) for bluntnose minnows and total copper was estimated to lie between 0.02 and 0.08.Bluntnose minnows held in control water for nine months ceased to spawn when they were exposed to 119.4 g/L total copper. Fish exposed to 119.4 g/L total copper for the same nine-month period began to spawn 60 days after being transferred to control water.     

Effects of triphenyltin on fish early life stages

Using a static-renewal procedure, effects of triphenyltin chloride (TPT) on hatching, survival, and morphology were assessed in early life stages of European minnows Phoxinus phoxinus. Embryonic-larval exposure at 16 and 21°C, and larval exposure at 16°C were compared. In the embryoniclarval exposure at 16°C, hatching was delayed and hatching success decreased at 15.9 g/L. Mortality increased at 3.9 g/L TPT, and complete mortality occurred after 7 and 9 days at 15.9 and 5.1 g/L, respectively. Mortality was higher at 21°C that at 16°C. Triphenyltin was more toxic to fish in larval stages. The induced effects were dose related, mortality increased at 1.8 g/L after 3 days, and was total after 5 days at 10.6 g/L. In all high TPT exposures, larvae developed skeletal malformations (bent tails), showed impaired swimming behavior or paralysis, and eyes became opaque. Marked histopathological alterations were found. Degenerative hydropic vacuolation of the cytoplasm were evident in skeletal muscles, skin, kidneys, corneal epithelium, lens, pigment layer of the retina and choroid, retina, and CNS including spinal cord. In severe cases, nuclear changes including pycnosis and karyorrhexis occurred. The observed toxicity of TPT was similar to that of tributyltin, but TPT acted more selectively on the lens and CNS, whereas other tissues were less affected. The study indicates that Phoxinus phoxinus larvae are negatively affected at peak TPT concentrations found in polluted environments.     

Effects of diquat on freshwater microbial communities

A static microcosm system was used to evaluate effects of the herbicide diquat (0.3–30 mg/L) on the structure and function of naturally derived microbial communities on polyurethane foam substrates. Microbial communities were exposed to a single application of diquat and were monitored for 21 days. Effects on community structure included changes in algal cell density at diquat concentrations 0.3 mg/L (after an initial decrease in net productivity), bacterial cell density (1 mg/L diquat), and increased biomass accumulation (10 and 30 mg/L diquat). The species richness of protozoa was reduced at diquat concentrations >0.3 mg/L; protozoan species composition was progressively more dissimilar with diquat treatment. Effects on community function included inhibition of net productivity and community respiration (10 and 30 mg/L diquat), and decreased enzyme activities [alkaline phosphatase (1, 10, and 30 mg/L diquat), electron transport system (0.3 mg/L diquat), and -glucosidase (0.3 mg/L diquat)]. Both photosynthetic and nonphotosynthetic organisms were affected by diquat. Most structural and functional responses were sensitive indicators of stress. Estimated chronic toxicity values ranged from 0.3 mg/L (day 3) to 5.5 mg/L (day 21). Most microbial responses indicated that microbial community structure and function did not recover within the 21-day exposure period.     

Sublethal Effects of Trace Metals (Cd,Cr, Cu,Hg) on Embryogenesis and Larval Settlement of the Ascidian <Emphasis Type="Italic">Ciona intestinalis</Emphasis>

Toxicity of Cadmium (Cd), Chromium (Cr), Copper (Cu), and Mercury (Hg) on the early developmental stages of Ciona intestinalis was investigated. Developmental defects of larvae after exposure of gametes throughout their development to the larval stage were assessed. Gamete exposure to increasing metal concentrations resulted in a significant decrease of the percentage of normally hatched larvae, showing median effective concentrations (EC₅₀) of 721 g/L (6.42 M) for Cd, 12772 g/L (226 M) for Cr, 36.6 g/L (0.576 M) for Cu, and 44.7 g/L (0.223 M) for Hg. Larval attachment was significantly affected when gametes were exposed to the metals throughout development. The EC₅₀ reducing larval attachment by 50% were 752 g/L (6.7 M) for Cd, 15026 g/L (289 M) for Cr, 67.8 g/L (1.607 M) for Cu, and 78.1 g/L (0.389 M) for Hg. Therefore, on a molar basis Hg is three times more toxic than Cu, 20–30 times more than Cd, and 700–1000 times more toxic than Cr, for both responses.     

Toxicity of microencapsulated permethrin to selected nontarget aquatic invertebrates

Microencapsulated permethrin (penncapthrin) was evaluated under laboratory conditions for its toxicity toward several nontarget aquatic invertebrates. Average LC50 estimates for selected lotic invertebrates, based on a one hour dosing regime, were: 2.71 mg/L forSimulium vittatum, 4.59 mg/L forHydropsyche spp., and 13.41 mg/L forIsonychia bicolor. In acute static tests withDaphnia magna, there was no significant difference (p0.05) between the toxicity of penncapthrin at 96 h (LC50 range: 6.80–22.5 g/L) and the EC formulation at 72 h (LC50 range: 0.6–21 g/L). Comparatively, the toxicity of microencapsulated methyl parathion (penncap-m) was not significantly different from that of penncapthrin towardD. magna, the former having LC50 estimates ranging form 0.3–12.25 g/L. LC50 estimates associated withDaphnia pulex ranged from 19 to 131 g/L. The toxicity of penncapthrin and penncap-m towardD. pulex was difficult to determine because of frequent control mortality due to food deprivation resulting from the need to run tests for longer than 48 h. In successful tests, LC50 estimates ranged from 19 to 28 g/L for penncapthrin and 0.08 to 25 g/L for penncap-m after 72 h exposure. In long term toxicity tests, 95% of D. magna at 1 g/L, 44% at 10 g/L, and 20% at 15 g/L survived after 39 days exposure. Less than 15% ofD. pulex survived over the same concentration range following 32 days exposure. Despite some drawbacks, long-term toxicity tests were more appropriate than short-term tests for evaluating microencapsulated sticides because of reduced variability in LC50 estimates and lower control mortality.     

Indoor air mercury concentrations following application of interior latex paint

Mercury vapors are released from paint containing mercury compounds used to prolong the shelf-life of interior latex paint. To determine whether homes recently painted with paint containing mercury had elevated indoor-air mercury concentrations, we studied 37 Ohio homes. Twenty-one homes painted with mercury-containing paint a median of 86 days earlier were compared with 16 homes not recently painted with mercury-containing paint. Paint samples from the exposed homes contained a median of 210 mg Hg/L (range 120–610 mg/L). The median air mercury concentration was higher in the exposed homes (0.3 g/m³; range nondetectable-1.5 g/m³) than in the unexposed homes (nondetectable; range nondetectable-0.3 g/m³, P < 0.0001). Among the exposed homes there were seven in which paint containing <200 mg/L had been applied. In these homes, the median air mercury concentration was 0.2 g/m³ (range nondetectable-1 g/m³). Six (33%) exposed homes had air mercury concentrations >0.5 g/m³, the acceptable indoor concentration recommended by the Agency for Toxic Substances and Disease Registry. Elemental mercury was the form of mercury released into the air. These data demonstrate that potentially hazardous mercury exposure may occur in homes recently painted with paint that contains mercury concentrations <200 mg/L.