A re-assessment of the safety of silver in household water treatment: rapid systematic review of mammalian in vivo genotoxicity studies.

BACKGROUND: Despite poor evidence of their effectiveness, colloidal silver and silver nanoparticles are increasingly being promoted for treating potentially contaminated drinking water in low income countries. Recently, however, concerns have been raised about the possible genotoxicity of particulate silver. OBJECTIVES: The goal of this paper was to review the published mammalian in vivo genotoxicity studies using silver micro and nanoparticles. METHODS: SCOPUS and Medline were searched using the following search string: ("DNA damage" OR genotox* OR Cytotox* OR Embryotox*) AND (silver OR AgNP). Included papers were any mammalian in vivo experimental studies investigating genotoxicity of silver particles. Studies were quality assessed using the ToxRTool. RESULTS: 16 relevant papers were identified. There were substantial variations in study design including the size of silver particles, animal species, target organs, silver dose, route of administration and the method used to detect genotoxicity. Thus, it was not possible to produce a definitive pooled result. Nevertheless, most studies showed evidence of genotoxicity unless using very low doses. We also identified one human study reporting evidence of "severe DNA damage" in silver jewellery workers occupationally exposed to silver particles. CONCLUSIONS: With the available evidence it is not possible to be definitive about risks to human health from oral exposure to silver particulates. However, the balance of evidence suggests that there should be concerns especially when considering the evidence from jewellery workers. There is an urgent need to determine whether people exposed to particulate silver as part of drinking water treatment have evidence of DNA damage.

Burden of disease from inadequate water, sanitation and hygiene in low- and middle-income settings: a retrospective analysis of data from 145 countries.

OBJECTIVE: To estimate the burden of diarrhoeal diseases from exposure to inadequate water, sanitation and hand hygiene in low- and middle-income settings and provide an overview of the impact on other diseases. METHODS: For estimating the impact of water, sanitation and hygiene on diarrhoea, we selected exposure levels with both sufficient global exposure data and a matching exposure-risk relationship. Global exposure data were estimated for the year 2012, and risk estimates were taken from the most recent systematic analyses. We estimated attributable deaths and disability-adjusted life years (DALYs) by country, age and sex for inadequate water, sanitation and hand hygiene separately, and as a cluster of risk factors. Uncertainty estimates were computed on the basis of uncertainty surrounding exposure estimates and relative risks. RESULTS: In 2012, 502,000 diarrhoea deaths were estimated to be caused by inadequate drinking water and 280,000 deaths by inadequate sanitation. The most likely estimate of disease burden from inadequate hand hygiene amounts to 297,000 deaths. In total, 842,000 diarrhoea deaths are estimated to be caused by this cluster of risk factors, which amounts to 1.5% of the total disease burden and 58% of diarrhoeal diseases. In children under 5 years old, 361,000 deaths could be prevented, representing 5.5% of deaths in that age group. CONCLUSIONS: This estimate confirms the importance of improving water and sanitation in low- and middle-income settings for the prevention of diarrhoeal disease burden. It also underscores the need for better data on exposure and risk reductions that can be achieved with provision of reliable piped water, community sewage with treatment and hand hygiene.

An estimation of the global burden of disease due to skin lesions caused by arsenic in drinking water.

The global burden of disease due to skin lesions caused by arsenic in drinking water was estimated by combining country-based exposure data with selected exposure-response relationships derived from the literature. Populations were considered to be exposed to elevated arsenic levels if their drinking water contained arsenic concentrations of 50 microg I(-1) or greater. Elevated arsenic concentrations in drinking water result in a significant global burden of disease, even when confining the health outcome to skin lesions. The burden of disease was particularly marked in the World Health Organization (WHO) comparative risk assessment (CRA) 'Sear D' region, which includes Bangladesh, India and Nepal. Unsurprisingly, Bangladesh was the worst affected country with 143 disability adjusted life years (DALYs) per 1,000 population. Although this initial estimate is subject to a large degree of uncertainty, it does represent an important first step in allowing the comparison of the problem relating to elevated arsenic in drinking water to other environmental health outcomes.

Drinking-water nitrate, methemoglobinemia, and global burden of disease: a discussion.

On behalf of the World Health Organization (WHO), I have undertaken a series of literature-based investigations examining the global burden of disease related to a number of environmental risk factors associated with drinking water. In this article I outline the investigation of drinking-water nitrate concentration and methemoglobinemia. The exposure assessment was based on levels of nitrate in drinking water greater than the WHO guideline value of 50 mg/L. No exposure-response relationship, however, could be identified that related drinking-water nitrate level to methemoglobinemia. Indeed, although it has previously been accepted that consumption of drinking water high in nitrates causes methemoglobinemia in infants, it appears now that nitrate may be one of a number of co-factors that play a sometimes complex role in causing the disease. I conclude that, given the apparently low incidence of possible water-related methemoglobinemia, the complex nature of the role of nitrates, and that of individual behavior, it is currently inappropriate to attempt to link illness rates with drinking-water nitrate levels.

Estimating the burden of disease from water, sanitation, and hygiene at a global level.

We estimated the disease burden from water, sanitation, and hygiene at the global level taking into account various disease outcomes, principally diarrheal diseases. The disability-adjusted life year (DALY) combines the burden from death and disability in a single index and permits the comparison of the burden from water, sanitation, and hygiene with the burden from other risk factors or diseases. We divided the world's population into typical exposure scenarios for 14 geographical regions. We then matched these scenarios with relative risk information obtained mainly from intervention studies. We estimated the disease burden from water, sanitation, and hygiene to be 4.0% of all deaths and 5.7% of the total disease burden (in DALYs) occurring worldwide, taking into account diarrheal diseases, schistosomiasis, trachoma, ascariasis, trichuriasis, and hookworm disease. Because we based these estimates mainly on intervention studies, this burden is largely preventable. Other water- and sanitation-related diseases remain to be evaluated. This preliminary estimation of the global disease burden caused by water, sanitation, and hygiene provides a basic model that could be further refined for national or regional assessments. This significant and avoidable burden suggests that it should be a priority for public health policy.