Wildfire burn severity and stream chemistry influence aquatic invertebrate and riparian avian mercury exposure in forested ecosystems

Terrestrial soils in forested landscapes represent some of the largest mercury (Hg) reserves globally. Wildfire can alter the storage and distribution of terrestrial-bound Hg via reemission to the atmosphere or mobilization in watersheds where it may become available for methylation and uptake into food webs. Using data associated with the 2007 Moonlight and Antelope Fires in California, we examined the long-term direct effects of wildfire burn severity on the distribution and magnitude of Hg concentrations in riparian food webs. Additionally, we quantified the cross-ecosystem transfer of Hg from aquatic invertebrate to riparian bird communities; and assessed the influence of biogeochemical, landscape variables, and ecological factors on Hg concentrations in aquatic and terrestrial food webs. Benthic macroinvertebrate methylmercury (MeHg) and riparian bird blood total mercury (THg) concentrations varied by 710- and 760-fold, respectively, and Hg concentrations were highest in predators. We found inconsistent relationships between Hg concentrations across and within taxa and guilds in response to stream chemical parameters and burn severity. Macroinvertebrate scraper MeHg concentrations were influenced by dissolved organic carbon (DOC); however, that relationship was moderated by burn severity (as burn severity increased the effect of DOC declined). Omnivorous bird Hg concentrations declined with increasing burn severity. Overall, taxa more linked to in situ energetic pathways may be more responsive to the biogeochemical processes that influence MeHg cycling. Remarkably, 8 years post-fire, we still observed evidence of burn severity influencing Hg concentrations within riparian food webs, illustrating its overarching role in altering the storage and redistribution of Hg and influencing biogeochemical processes.

Gene Expression Profiling of Di-n-Butyl Phthalate in Normal Human Mammary Epithelial Cells

Studies show that female workers in the personal-care industry have an increased risk of developing cancer believed to be the result of increased exposure to toxic and/or carcinogenic chemicals found in cosmetics, hair dyes, and nail polish. One chemical found in multiple personal-care products, di-n-butyl phthalate (DBP), is a known endocrine disruptor and has been found in increased levels in women of childbearing age. The goal of this study was to elucidate mechanisms of phthalate toxicity in normal human cells to provide information concerning interindividual variation and gene-environment interactions. Normal human mammary epithelial cell strains were obtained from discarded tissues following reduction mammoplasty [Cooperative Human Tissue Network (sponsors: NCI/NDRI)]. Gene transcription in each cell strain was analyzed using high-density oligonucleotide DNA microarrays (U133A, Affymetrix) and changes in the expression of selected genes were verified by real-time polymerase chain reaction (PCR) (ABI). DNA microarrays were hybridized with total RNA that was collected after DBP treatment for 5 hr and 10 hr. RNA was harvested from the vehicle control (acetone) at 10 hr. Data Mining Tool software (Affymetrix) was used to separate genes in clusters based on their expression patterns over time. Only 57 genes were found to be altered in all four cell strains following exposure to DBP. These included genes involved in fertility (inhibin, placental growth factor), immune response (tumor necrosis factor induced protein), and antioxidant status (glutathione peroxidase). Data from this study will help clarify the role of DBP in reproductive toxicity, and yield biomarkers of exposure for future epidemiology studies.

Differential gene expression in normal human mammary epithelial cells treated with malathion monitored by DNA microarrays

Organophosphate pesticides are a major source of occupational exposure in the United States. Moreover, malathion has been sprayed over major urban populations in an effort to control mosquitoes carrying West Nile virus. Previous research, reviewed by the U.S. Environmental Protection Agency, on the genotoxicity and carcinogenicity of malathion has been inconclusive, although malathion is a known endocrine disruptor. Here, interindividual variations and commonality of gene expression signatures have been studied in normal human mammary epithelial cells from four women undergoing reduction mammoplasty. The cell strains were obtained from the discarded tissues through the Cooperative Human Tissue Network (sponsors: National Cancer Institute and National Disease Research Interchange). Interindividual variation of gene expression patterns in response to malathion was observed in various clustering patterns for the four cell strains. Further clustering identified three genes with increased expression after treatment in all four cell strains. These genes were two aldo-keto reductases (AKR1C1 and AKR1C2) and an estrogen-responsive gene (EBBP). Decreased expression of six RNA species was seen at various time points in all cell strains analyzed: plasminogen activator (PLAT), centromere protein F (CPF), replication factor C (RFC3), thymidylate synthetase (TYMS), a putative mitotic checkpoint kinase (BUB1), and a gene of unknown function (GenBank accession no. AI859865). Expression changes in all these genes, detected by DNA microarrays, have been verified by real-time polymerase chain reaction. Differential changes in expression of these genes may yield biomarkers that provide insight into interindividual variation in malathion toxicity.

Paralysis of the preterm rabbit fetus inhibits the pulmonary uptake of intraamniotic iron dextran

OBJECTIVE

Whether fetal breathing movements or gasping result in the movement of amniotic fluid substances into the distal airways remains controversial. We evaluated the effect of paralysis of the preterm rabbit fetus on the pulmonary distribution of iron dextran.

STUDY DESIGN

Laparotomy was performed on 10 New Zealand White rabbits of 25 days' gestation (term 31 days) under general anesthesia. Fetuses in one uterine horn were given an intramuscular injection of pancuronium (1.5 mg/kg) and fetuses in the other horn were given an equal volume of normal saline solution as controls. A 1 ml volume of iron dextran (100 mg/ml) was injected into the amniotic sac of all fetuses. The laparotomy was closed, and 20 to 24 hours later the fetuses were removed by hysterotomy and assessed for paralysis. Necropsy was performed. Lungs were stained with prussian blue and evaluated histologically for the presence of iron.

RESULTS

A total of 92 pups were delivered (49 given pancuronium, 43 given normal saline solution), of which 64 were born alive. There were no differences between groups for live births (31 pancuronium, 33 normal saline solution), pup body weight, or lung weight. Pups given normal saline solution demonstrated more breathing motions, spontaneous movement, and brown (color of iron dextran) stomach contents than did the pups given pancuronium (p < 0.001). At necropsy a greater number of control pups (31/33) had brown lungs grossly compared with pups given pancuronium (2/31, p < 0.001). Lung histologic examination showed that more control pups (29/29) had iron in the trachea and main bronchi compared with pancuronium pups (0/27, p < 0.001), and more control pups (29/29) had iron in the distal lung airways compared with pancuronium pups (0/27, p < 0.001). With use of the Optimas Image Analysis System, iron in the lungs of control pups was found to be equally distributed between right versus left lungs, upper half versus lower half lungs, and anterior versus posterior lung sections. More iron was identified in the central airways than in the periphery (p < 0.001).

CONCLUSION

We conclude that paralysis prevents the uptake of iron dextran into the main and distal airways of the rabbit fetus. Although lung fluid production results in a net efflux of fluid, we speculate that fetal breathing movements can result in the movement of fluid into distal airways and potentially provide fetal therapy.