I gave up taking psyllium husk because it tends to be contaminated with lead.
Blood lead levels can vary with season due to seasonal changes in bone resorption rates.
Season modifies the relationship between bone and blood lead levels: the Normative Aging Study
https://pubmed.ncbi.nlm.nih.gov/12641191/
Makes me wonder if people who move to lower latitudes when they retire are on to something.