Use of lanthanum for water treatment A matter of concern?

Among several other eutrophication management tools, Phoslock®, a lanthanum modified bentonite (LMB) clay, is now frequently used. Concerns have been raised as to whether exposure to Phoslock®-treated water may lead to lanthanum accumulation/toxicity in both animals and humans. In the present experimental study, rats were administered lanthanum orally as either lanthanum carbonate, lanthanum chloride or Phoslock® at doses of either 0.5 or 17 mg/L during 10 weeks. Controls received vehicle. The gastrointestinal absorption and tissue distribution of lanthanum was investigated. Extremely strict measures were implemented to avoid cross-contamination between different tissues or animals. Results showed no differences in gastrointestinal absorption between the different compounds under study as reflected by the serum lanthanum levels and concentrations found in the brain, bone, heart, spleen, lung, kidney and testes. At sacrifice, significant but equally increased lanthanum concentrations versus vehicle were observed in the liver for the highest dose of each compound which however, remained several orders of magnitude below the liver lanthanum concentration previously measured after long-term therapeutic administration of lanthanum carbonate and for which no hepatotoxicity was noticed in humans. In conclusion, (i) the use of LMB does not pose a toxicity risk (ii) gastrointestinal absorption of lanthanum is minimal and independent on the type of the compound, (iii) with exception of the liver, no significant increase in lanthanum levels is observed in the various organs under study, (iv) based on previous studies, the slightly increased liver lanthanum levels observed in a worst case scenario do not hold any risk of hepatotoxicity.

Human inflammatory response of endotoxin affected by particulate matter-bound transition metals.

Bacterial endotoxins are a component of particulate matter (PM) with anticipated health implications, yet we know little about how host reception of endotoxin through toll-like receptor 4 (TLR4) is affected by its association with other PM components. Subsequently, we investigated the relationship between endotoxin concentration (recombinant Factor C (rFC) assay) and host recognition (HEK Blue-TLR4 NF-kB reporter cell line based assay) in various compositions of urban PM, including road traffic, industrial and urban green land use classes. While the assays did not correlate strongly between each other, the TLR4 reporter cell line was found to be better correlated to the IL-8 response of PM. Furthermore, the ability of the quantified endotoxin (rFC assay) to stimulate the TLR4/MD-2 complex was significantly affected by the urban land use class, where traffic locations were found to be significantly higher in bioactive endotoxin than the industrial and green locations. We subsequently turned our attention to PM composition and characterized the samples based on transition metal content (through ICP-MS). The effect of nickel and cobalt - previously reported to activate the hTLR4/MD-2 complex - was found to be negligible in comparison to that of iron. Here, the addition of iron as a factor significantly improved the regression model between the two endotoxin assays, explaining 77% of the variation of the TLR4 stimulation and excluding the significant effect of land use class. Moreover, the effect of iron proved to be more than a correlation, since dosing LPS with Fe2+ led to an increase up to 64% in TLR4 stimulation, while Fe2+ without LPS was unable to stimulate a response. This study shows that endotoxin quantification assays (such as the rFC assay) may not always correspond to human biological recognition of endotoxin in urban PM, while its toxicity can be synergistically influenced by the associated PM composition.