Freshwater mussels in an impacted watershed: Influences of pollution from point and non-point sources

The Grand River watershed in a densely populated region of Ontario supports one of the richest assemblages of freshwater mussels in Canada. However, water quality in this watershed is influenced by urban development, agriculture, and industry. Mussel populations and water chemistry in the lower Grand River and the Boston Creek tributary were evaluated to determine whether point sources of pollution such as discharges of domestic wastewater and industrial effluent, and non-point sources of pollution are affecting mussel distribution and population structure. Semi-quantitative population surveys conducted at 9 study sites identified 20 mussel species, including 3 Species at Risk. Mussel abundance (34-160 mussels/search hour) and species richness indicated that mussel populations in the lower Grand River watershed are continuing to recover from historical lows reported in the 1970s. However, changes in populations at some sites were consistent with altered water chemistry. Most notable was that the three most abundant mussel species in the Boston Creek tributary downstream of a gypsum plant discharge were significantly smaller in length than those upstream of this site. The water chemistry in this habitat was characterized by elevated conductivity (∼2000 μS/cm) and calcium (∼500 mg/L), as well as concentrations of sulfate (∼1000 mg/L) that can be toxic to freshwater mussels. In the Grand River downstream of the confluence with Boston Creek, there tended to be (p > 0.05) fewer mussels (mean 34 ± 20/search h) compared to upstream (mean 67 ± 15/search h) and this corresponded to altered water chemistry, including elevated sulfate (239 mg/L) downstream of the confluence relative to upstream (58 mg/L). These data indicate that chronic exposures to high levels of major ions is likely driving changes to mussel population structure. In addition, the discharges of wash water from a gypsum plant may be impacting sensitive biota in the main stem Grand River well beyond the immediate tributary receiving environment.

Toxic Thyroid Nodule: To FNA or Not?

Background: ATA guidelines recommend evaluation of hyperthyroidism with radioiodine scan and consideration of FNA for non-toxic nodules with suspicious sonographic features. However, there is no standard evidence-based approach to performing ultrasound in patients with toxic nodules. Recent studies have shown increased rates of thyroid cancer in patients with hyperthyroidism and has been shown to demonstrate aggressive histologic features. Clinical Case: A 41-year-old female presented to primary care provider for annual physical exam, found to have intermittent bigeminy and enlarged thyroid on exam. EKG notable for multiple premature ventricular complexes. Evaluation revealed suppressed TSH <0.01 µIU/mL (0.27-4.20), normal free T4 1.27 ng/dL (0.80-1.80), slightly elevated free T3 4.84 pg/mL (2.57-4.43) and elevated TSI 238% (<122). Methimazole was started for treatment of hyperthyroidism. Thyroid sonogram was ordered for abnormal exam, that showed 2.7 cm TIRADS 4 left thyroid nodule with microcalcifications. I-131 uptake values were 20% and 49% at 4-hours and 24-hours, respectively. Technetium-99M scan showed toxic autonomous nodule in the left thyroid lobe corresponding to the one seen on sonogram. The remainder of the thyroid gland showed heterogeneously suppressed uptake. FNA of the thyroid nodule was done due to the presence of microcalcifications and the cytopathology was suspicious for papillary carcinoma. She underwent total thyroidectomy with central neck dissection involving pre-tracheal and paratracheal lymph nodes (level VI). Pathology showed 1.4 cm papillary carcinoma with lymphovascular space invasion and multifocal papillary microcarcinomas in the left thyroid lobe, 0.2 cm papillary microcarcinoma in right thyroid lobe, metastatic papillary carcinoma in 2 out of 5 lymph nodes, largest metastatic deposit 0.1 cm in the largest dimension with no extra nodal extension. There was also follicular hyperplasia noted consistent with Graves’ disease. Post-operatively, she had thyrogen-stimulated adjuvant RAI treatment, dose 107.4 mCi. Post therapy scan did not show evidence of distant metastases. Conclusion: This case demonstrates the identification of a metastatic papillary thyroid carcinoma based on suspicious ultrasound features requiring total thyroidectomy, central neck dissection and adjunct radioactive iodine in a patient with hyperthyroidism from co-existent toxic thyroid nodule and Graves’ disease.