Nanoparticles in the environment: assessment using the causal diagram approach

Abstract

Nanoparticles (NPs) cause concern for health and safety as their impact on the environment and humans is not known. Relatively few studies have investigated the toxicological and environmental effects of exposure to naturally occurring NPs (NNPs) and man-made or engineered NPs (ENPs) that are known to have a wide variety of effects once taken up into an organism. A review of recent knowledge (between 2000-2010) on NP sources, and their behaviour, exposure and effects on the environment and humans was performed. An integrated approach was used to comprise available scientific information within an interdisciplinary logical framework, to identify knowledge gaps and to describe environment and health linkages for NNPs and ENPs. The causal diagram has been developed as a method to handle the complexity of issues on NP safety, from their exposure to the effects on the environment and health. It gives an overview of available scientific information starting with common sources of NPs and their interactions with various environmental processes that may pose threats to both human health and the environment. Effects of NNPs on dust cloud formation and decrease in sunlight intensity were found to be important environmental changes with direct and indirect implication in various human health problems. NNPs and ENPs exposure and their accumulation in biological matrices such as microbiota, plants and humans may result in various adverse effects. The impact of some NPs on human health by ROS generation was found to be one of the major causes to develop various diseases. A proposed cause-effects diagram for NPs is designed considering both NNPs and ENPs. It represents a valuable information package and user-friendly tool for various stakeholders including students, researchers and policy makers, to better understand and communicate on issues related to NPs.

Figure 1

Proposed cause-effect diagram of NPs on environment and human health

Figure 2

Common sources of NPs in the environment.

Figure 3

Impact of NPs on dust cloud formation and decrease in sunlight intensity and relation with various human health problems

Figure 4

Schematic diagram how NPs are affecting the hydroxyl radical concentration, resulting in ozone depletion and human health problems

Figure 5

Effect of NPs on the increase in water vapour in stratosphere and decrease in stratospheric temperature resulting in various allergic diseases

Figure 6

Exposure of NPs to plants, microbes and lower organisms resulting in adverse impact

Figure 7

Effect of NPs on plants NPs may enter into the plants via (A) stomatal cells. NPs entered through stomata may deposit into the cellular system and can affect transpiration, plants respiration, photosynthesis. (B) NPs can deposit on sieve cells and interfere with the translocation of food material and block xylem cells. (C) NPs in soils may enter through the active or passive absorption by root hairs.

Figure 8

NPs exposure causes target organs toxicity by ROS formation and apoptosis resulting in adverse impact on human health