Paul Westerhoff

Titanium dioxide nanoparticles in food and personal care products.

Titanium dioxide is a common additive in many food, personal care, and other consumer products used by people, which after use can enter the sewage system and, subsequently, enter the environment as treated effluent discharged to surface waters or biosolids applied to agricultural land, incinerated wastes, or landfill solids. This study quantifies the amount of titanium in common food products, derives estimates of human exposure to dietary (nano-) TiO(2), and discusses the impact of the nanoscale fraction of TiO(2) entering the environment. The foods with the highest content of TiO(2) included candies, sweets, and chewing gums. Among personal care products, toothpastes and select sunscreens contained 1% to >10% titanium by weight. While some other crèmes contained titanium, despite being colored white, most shampoos, deodorants, and shaving creams contained the lowest levels of titanium (<0.01 μg/mg). For several high-consumption pharmaceuticals, the titanium content ranged from below the instrument detection limit (0.0001 μg Ti/mg) to a high of 0.014 μg Ti/mg. Electron microscopy and stability testing of food-grade TiO(2) (E171) suggests that approximately 36% of the particles are less than 100 nm in at least one dimension and that it readily disperses in water as fairly stable colloids. However, filtration of water solubilized consumer products and personal care products indicated that less than 5% of the titanium was able to pass through 0.45 or 0.7 μm pores. Two white paints contained 110 μg Ti/mg while three sealants (i.e., prime coat paint) contained less titanium (25 to 40 μg Ti/mg). This research showed that, while many white-colored products contained titanium, it was not a prerequisite. Although several of these product classes contained low amounts of titanium, their widespread use and disposal down the drain and eventually to wastewater treatment plants (WWTPs) deserves attention. A Monte Carlo human exposure analysis to TiO(2) through foods identified children as having the highest exposures because TiO(2) content of sweets is higher than other food products and that a typical exposure for a US adult may be on the order of 1 mg Ti per kilogram body weight per day. Thus, because of the millions of tons of titanium-based white pigment used annually, testing should focus on food-grade TiO(2) (E171) rather than that adopted in many environmental health and safety tests (i.e., P25), which is used in much lower amounts in products less likely to enter the environment (e.g., catalyst supports, photocatalytic coatings).

Pharmaceuticals, Personal Care Products, and Endocrine Disruptors in Water: Implications for the Water Industry

For over 70 years, scientists have reported that certain synthetic and natural compounds could mimic natural hormones in the endocrine systems of animals. These substances are now collectively known as endocrine-disrupting compounds (EDCs), and have been linked to a variety of adverse effects in both humans and wildlife. More recently, pharmaceuticals and personal care products (PPCPs) have been discovered in various surface and ground waters, some of which have been linked to ecological impacts at trace concentrations. The majority of EDCs and PPCPs are more polar than traditional contaminants and several have acidic or basic functional groups. These properties, coupled with occurrence at trace levels (i.e., <1 μg/L), create unique challenges for both removal processes and analytical detection. Reports of EDCs and PPCPs in water have raised substantial concern among the public and regulatory agencies; however, very little is known about the fate of these compounds during drinking and wastewater treatment...

Stability of commercial metal oxide nanoparticles in water

The fate of commercial nanoparticles in water is of significant interest to health and regulatory authorities. This research investigated the dispersion and stability of metal oxide nanoparticles in water as well as their removal by potable water treatment processes. Commercial nanoparticles were received as powder aggregates, and in water neither ultrasound nor chemical dispersants could break them up into primary nanoparticles. Lab-synthesized hematite was prepared as a primary nanoparticle (85 nm) suspension; upon drying and 1-month storage, however, hematite formed aggregates that could not be dispersed completely as primary nanoparticles in water. This observation may explain why it is difficult to disperse dry commercial nanoparticles. Except for silica, other nanoparticles rapidly aggregated in tap water due to electric double layer (EDL) compression. The stability of silica in tap water is related to its low Hamaker constant. For all these nanoparticles, at an alum dosage of 60 mg/L, coagulation followed by sedimentation could remove 20-60% of the total nanoparticle mass. Filtration using a 0.45 microm filter was required to remove more than 90% of the nanoparticle mass.

Impact of natural organic matter and divalent cations on the stability of aqueous nanoparticles.

The stability of nanoparticles in aquatic environment plays an important role in determining their environmental implication and potential risk to human health. This research studied the impact of natural organic matter (NOM) and divalent cations (Ca(2+)) on the stability of engineered metal oxide nanoparticles (e.g. ZnO, NiO, TiO(2), Fe(2)O(3) and SiO(2)). When nanoparticles were present in neutral water, a relatively weak electrolyte concentration (0.01 M KCl) could result in their aggregation; however, with the addition of 1 mg/L NOM, the negative surface charge of nanoparticles increased significantly and therefore their propensity to aggregate is reduced. 4 mg/L NOM stabilized most nanoparticles by producing -30 mV or higher zeta potentials. On the other hand, the negative charge that NOM imparted to nanoparticles could be neutralized by divalent cations (calcium ions). 0.04 M-0.06 M Ca(2+) induced the aggregation of NOM-coated nanoparticles. It should be noted that among all the studied nanoparticles, SiO(2) exhibited the unique stability due to its low NOM adsorption capacity and small Hamaker constant. SiO(2) remained stable no matter whether the solution contained NOM or Ca(2+).

Occurrence and removal of titanium at full scale wastewater treatment plants: implications for TiO2 nanomaterials

Titanium dioxide nanoparticles increasingly will be used in commercial products and have a high likelihood of entering municipal sewage that flows to centralized wastewater treatment plants (WWTPs). Treated water (effluent) from WWTPs flows into rivers and lakes where nanoparticles may pose an ecological risk. To provide exposure data for risk assessment, titanium concentrations in raw sewage and treated effluent were determined for 10 representative WWTPs that use a range of unit processes. Raw sewage titanium concentrations ranged from 181 to 1233 µg L(-1) (median of 26 samples was 321 µg L(-1)). The WWTPs removed more than 96% of the influent titanium, and all WWTPs had effluent titanium concentrations of less than 25 µg L(-1). To characterize the morphology and presence of titanium oxide nanoparticles in the effluent, colloidal materials were isolated via rota-evaporation, dialysis and lyophilization. High resolution transmission electron microscopy and energy dispersive X-ray analysis indicated the presence of spherical titanium oxide nanoparticles (crystalline and amorphous) on the order of 4 to 30 nm in diameter in WWTP effluents. This research provides clear evidence that some nanoscale particles will pass through WWTPs and enter aquatic systems and offers a methodological framework for collecting and analyzing titanium-based nanomaterials in complex wastewater matrices.

HPLC-fluorescence detection and adsorption of bisphenol A, 17β-estradiol, and 17α-ethynyl estradiol on powdered activated carbon

The adsorption of three estrogenic compounds (bisphenol A (BPA), 17beta-estradiol (E2), and 17alpha-ethynyl estradiol (EE2)) on several powdered activated carbons (PAC) was investigated. Without preconcentration, method detection limits (MDL) using high-performance liquid chromatography (HPLC) with fluorescence detection at an excitation wavelength of 280 nm and an emission wavelength of 310 nm were 0.88, 1.15, and 0.96 nM for BPA, E2, and EE2, respectively. Compound recoveries were >90% in raw drinking water matrices. PAC screening studies (six PAC brands) indicated all three compounds were removed by PAC, but the percentage removal ranged from 31% to >99% based upon PAC type/dosage and presence/absence of natural organic matter. The order of removal (E2>EE2>BPA) corresponded with logK(ow) values for the compounds (3.1-4.0, 3.7-3.9, 3.3, respectively). Kinetic and PAC dose-response experiments were conducted with the two best performing PACs. Increasing contact time and PAC dose improved compound removal. Freundlich isotherm parameters were fit to the experimental data. This study confirms that PAC treatment is feasible for >99% removal of three estrogenic compounds from raw drinking waters that may be at risk for containing such compounds, at least at initial concentration of 500 ng/l and higher.

Nitrate removal in zero-valent iron packed columns

Nitrate removal by laboratory and field continuous-flow zero-valent iron (Fe(0)) packed bed columns was evaluated for different influent water qualities (pH, dissolved oxygen (DO), nitrate concentration) and several months of operation (600-1500 bed volumes (BVs)). In contrast to previous batch experiments with Fe(0) where nitrate was stoichiometrically converted to ammonium, only 70% of the applied nitrogen was recovered as nitrate, ammonium, or nitrite (<0.1mg/L) during shorter-term column tests (2-20 BVs) and less than 25% of the applied nitrogen was recovered during longer-term field testing (500-1000 BVs) at elevated nitrate levels (approximately 25mg N/L). Nitrate removal was accompanied by a pH increase, DO decrease, and soluble iron increase. During longer-term operation (500-1500 BVs) iron and calcium precipitates were observed, by SEM and EDX analyses, to form in the packed columns. Precipitation led to cementation and reduction in permeability for the Fe(0)/sand media in the packed column. Different abiotic and microbial-mediated mechanisms may be involved during shorter- and longer-term operation of Fe(0) systems and the role of iron precipitates should be further evaluated.

Occurrence of disinfection byproducts in United States wastewater treatment plant effluents

Effluents from wastewater treatment plants (WWTPs) contain disinfection byproducts (DBPs) of health concern when the water is utilized downstream as a potable water supply. The pattern of DBP formation was strongly affected by whether or not the WWTP achieved good nitrification. Chlorine addition to poorly nitrified effluents formed low levels of halogenated DBPs, except for (in some cases) dihalogenated acetic acids, but often substantial amounts of N-nitrosodimethyamine (NDMA). Chlorination of well-nitrified effluent typically resulted in substantial formation of halogenated DBPs but much less NDMA. For example, on a median basis after chlorine addition, the well-nitrified effluents had 57 microg/L of trihalomethanes [THMs] and 3 ng/L of NDMA, while the poorly nitrified effluents had 2 microg/L of THMs and 11 ng/L of NDMA. DBPs with amino acid precursors (haloacetonitriles, haloacetaldehydes) formed at substantial levels after chlorination of well-nitrified effluent. The formation of halogenated DBPs but not that of NDMA correlated with the formation of THMs in WWTP effluents disinfected with free chlorine. However, THM formation did not correlate with the formation of other DBPs in effluents disinfected with chloramines. Because of the relatively high levels of bromide in treated wastewater, bromine incorporation was observed in various classes of DBPs.

Biosorption of nanoparticles to heterotrophic wastewater biomass

Sorption to activated sludge is a major removal mechanism for pollutants, including manufactured nanoparticles (NPs), in conventional activated sludge wastewater treatment plants. The objectives of this work were to (1) image sorption of fluorescent NPs to wastewater biomass; (2) quantify and compare biosorption of different types of NPs exposed to wastewater biomass; (3) quantify the effects of natural organic matter (NOM), extracellular polymeric substances (EPS), surfactants, and salt on NP biosorption; and (4) explore how different surface functionalities for fullerenes affect biosorption. Batch sorption isotherm experiments were conducted with activated sludge as sorbent and a total of eight types of NPs as sorbates. Epifluorescence images clearly show the biosorption of fluorescent silica NPs; the greater the concentration of NPs exposed to biomass, the greater the quantity of NPs that biosorb. Furthermore, biosorption removes different types of NPs from water to different extents. Upon exposure to 400 mg/L total suspended solids (TSS) of wastewater biomass, 97% of silver nanoparticles were removed, probably in part by aggregation and sedimentation, whereas biosorption was predominantly responsible for the removal of 88% of aqueous fullerenes, 39% of functionalized silver NPs, 23% of nanoscale titanium dioxide, and 13% of fullerol NPs. Of the NP types investigated, only aq-nC(60) showed a change in the degree of removal when the NP suspension was equilibrated with NOM or when EPS was extracted from the biomass. Further study of carbonaceous NPs showed that different surface functionalities affect biosorption. Thus, the production and transformations in NP surface properties will be key factors in determining their fate in the environment.

Formation, precursors, control, and occurrence of nitrosamines in drinking water: A review

This review summarizes major findings over the last decade related to nitrosamines in drinking water, with a particular focus on N-nitrosodimethylamine (NDMA), because it is among the most widely detected nitrosamines in drinking waters. The reaction of inorganic dichloramine with amine precursors is likely the dominant mechanism responsible for NDMA formation in drinking waters. Even when occurrence surveys found NDMA formation in chlorinated drinking waters, it is unclear whether chloramination resulted from ammonia in the source waters. NDMA formation has been associated with the use of quaternary amine-based coagulants and anion exchange resins, and wastewater-impaired source waters. Specific NDMA precursors in wastewater-impacted source waters may include tertiary amine-containing pharmaceuticals or other quaternary amine-containing constituents of personal care products. Options for nitrosamine control include physical removal of precursors by activated carbon or precursor deactivation by application of oxidants, particularly ozone or chlorine, upstream of chloramination. Although NDMA has been the most prevalent nitrosamine detected in worldwide occurrence surveys, it may account for only ≈ 5% of all nitrosamines in chloraminated drinking waters. Other significant contributors to total nitrosamines are poorly characterized. However, high levels of certain low molecular weight nitrosamines have been detected in certain Chinese waters suspected to be impaired by industrial effluents. The review concludes by identifying research needs that should be addressed over the next decade.