HEAVY METAL FORAMS: TEST ANALYSIS REDUX

Living benthic foraminifera in shallow Texas bays are subject to a host of environmental stressors including swings in salinity, temperature, and dissolved oxygen, as well as metal pollution in the sediment. Though population numbers are healthy in most bays sampled, signs of stress include shell dissolution and framboidal pyrite formation inside tests and in the substrate.

To better understand the role of heavy metal contamination on foraminifera, major and minor elements (including Mn, Fe, Zn, Cd, Ba, Pb, Ni, and Cu) in living Ammonia parkinsoniana shells from Copano, Mesquite, Mission, and Nueces Bays were first analyzed with ICP-MS in 2018. The preliminary results showed that A. parkinsoniana is incorporating these elements into its tests approximately proportionally to the amounts found in sediment. However, small sample sizes may have rendered some data unreliable, and specimens from Mesquite Bay, the least impacted site, disintegrated during cleaning, making re-analysis desirable.

For the current research, a larger number of “living” (stained with rose Bengal at the time of collection) A. parkinsoniana tests from the same bays were again run with ICP-MS. Both Pb and Ba compare well with the first run, and along with Zn and Cu are elevated orders of magnitude higher than in predicted pristine shell values. It is likely that the presence of excess metals contributes to the dissolution and pyritization observed in most bays. Many studies have dealt with the effects of heavy metal pollution on foraminiferal abundance and shell deformation, but this is one of the few that focuses on test analysis.