Seasonal changes in whole-cell metal levels in protozoa of activated sludge

In this study the authors quantify, and correlate, whole-cell elemental levels of vorticellids in activated sludge, over a 1-year period, and Aspidisca cicada and Opercularia coarctata on one sampling date. The aim was to determine the extent, and seasonal variation, of metal uptake and/or accumulation, to give new information regarding the fate and dynamics of the cellular elements, and to determine how they are related to each other over time and between species, in an environment exposed to high levels of heavy metals. Samples of activated sludge were collected monthly, and whole-cell elemental levels of vorticellids determined by scanning electron microscopy electron probe X-ray microanalysis (XRMA). Positive intersample correlations were found between phosphorus and three elements, sulfur, potassium, and iron. Potassium and calcium levels correlated positively with sulfur levels. Iron levels were positively correlated with potassium levels. Levels in A. cicada sampled from activated sludge were also compared with the same species grown in vitro, previously isolated from the same sewage treatment works. The level of cellular elements varies considerably with time, and between species from the same environment. Vorticellids could tolerate varying levels of aluminum, copper, iron, and zinc. Decreased iron levels were associated with decreased phosphorus and potassium levels.