Agriculture Reference
In-Depth Information
concentrations and at the same time retain the chemical and physical state are
needed.
Based on the available information, most uptake and accumulation studies
reported in the literature were conducted in hydroponic systems with young seed-
lings. However, it is clear from a few limited studies that the uptake and accumu-
lation of ENMs by plants is directly affected by the properties of growing media
such as the nature and quantity of natural organic matter, moisture, and pH; the
plant species (e.g., monocot vs. dicot); and, most importantly, the physicochemical
properties of ENMs. The unique correlation of these parameters with the uptake and
accumulation of ENMs by agricultural crops has not been established, yet it is
critically important to predict the potential accumulation of ENMs by food crops.
One important aspect which is not covered in this chapter is the bioaccessibility of
ENMs in plant tissues. It should be understood that the consumption of food crops
containing ENMs will not necessarily result in similar bioavailability of ENMs as
the consumption of food crops containing equivalent amount of ions or other
chemical forms of the same material. The extent of absorption of ENMs by the
membranes in digestive systems and their bioavailability and health risks following
consumption of ENM-containing crops need further investigation.
As has been shown, the impact of ENMs is not limited to their direct effect on
crop growth and their potential accumulation and bioaugmentation in the food
chain. ENMs interact closely with environmental pollutants and alter their plant
uptake and accumulation in agricultural systems. Limited study has demonstrated
that ENMs with different properties displayed different effects on the accumulation
of coexisting environmental pollutants by plants, but studies have not been
performed to evaluate the role of the physicochemical properties of coexisting
contaminants in this process. In addition, all of the previous studies limited to
evaluating the alteration of fate and transport of organic compounds by ENMs and
the impact of ENMs on the uptake and transport of heavy metals have not been
assessed. In addition to the modification on the uptake and accumulation of
co-present environmental chemicals, ENMs are able to affect the accumulation of
some macro- and micronutrients which directly affect the nutritional values of
agricultural products. The extent of effect, however, is not known. The issues raised
above all hold some importance to the applications and implications of ENMs in
agricultural industry and warrant further investigation in the future.
14.7 Conclusion
In closing, we reviewed the available literature concerning the interactions of
several agriculturally important ENMs with crops and presented our assessment
on this important issue. Based on the available information, it is clear that ENMs
interfere with crop development at both physiological and molecular levels. The
interface could be both enhancive and inhibitive for the same ENMs, and the
exposure concentration appeared to be critically important. The safe threshold
