Phytotoxicity describes any adverse effects on plant growth,

physiology Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...

, or metabolism caused by a

chemical substance A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be com ...

, such as high levels of fertilizers, herbicides, heavy metals, or

nanoparticle A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At ...

s. General phytotoxic effects include altered plant metabolism, growth inhibition, or plant death. Changes to plant metabolism and growth are the result of disrupted physiological functioning, including inhibition of

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

, water and nutrient uptake,

cell division Cell division is the process by which a parent cell (biology), cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukar ...

, or seed germination.

Fertilizers

High concentrations of mineral salts in solution within the plant growing medium can result in phytotoxicity, commonly caused by excessive application of

fertilizer A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Man ...

s. For example,

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

is used in agriculture as a nitrogenous fertilizer. However, if too much is applied, phytotoxic effects can result from urea toxicity directly or ammonia production from

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of urea. Organic fertilizers, such as

compost Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by Decomposition, decomposing plant and food waste, recycling organic materials, and man ...

, also have the potential to be phytotoxic if not sufficiently humified, as intermediate products of this process are harmful to plant growth.

Herbicides

Herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

s are designed and used to control unwanted plants such as agricultural weeds. However, the use of herbicides can cause phytotoxic effects on non-targeted plants through wind-blown spray drift or from the use of herbicide-contaminated material (such as straw or manure) being applied to the soil. Herbicides can also cause phytotoxicity in crops if applied incorrectly, in the wrong stage of crop growth, or in excess. The phytotoxic effects of herbicides are an important subject of study in the field of

ecotoxicology Ecotoxicology is the study of the effects of toxic chemicals on biological organisms, especially at the population biology, population, biological community, community, ecosystem, and biosphere levels. Ecotoxicology is a multidisciplinary field, ...

Heavy Metals

Heavy metals are high-density metallic compounds which are poisonous to plants at low concentrations, although toxicity depends on plant species, specific metal and its chemical form, and soil properties. The most relevant heavy metals contributing to phytotoxicity in crops are

silver Silver is a chemical element; it has Symbol (chemistry), symbol Ag () and atomic number 47. A soft, whitish-gray, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. ...

(Ag),

arsenic Arsenic is a chemical element; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...

(As),

cadmium Cadmium is a chemical element; it has chemical symbol, symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12 element, group 12, zinc and mercury (element), mercury. Like z ...

(Cd),

cobalt Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...

(Co),

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

(Cr),

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

(Fe),

nickel Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

(Ni),

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

(Pb), and

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...

(Zn). Of these, Co, Cu, Fe, Ni, and Zn are trace elements required in small amounts for enzyme and

redox reactions Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

essential in plant development. However, past a certain threshold they become toxic. The other heavy metals listed are considered toxic at any concentration and can

bioaccumulate Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance faster than it can be lost or eliminated by catabolism and excretion. Th ...

, posing a health hazard to humans if consumed. Heavy metal contamination occurs from both natural and anthropogenic sources. The most notable natural source of heavy metals is rock outcroppings, although volcanic eruptions can release large amounts of toxic material. Significant anthropogenic sources include

mining Mining is the Resource extraction, extraction of valuable geological materials and minerals from the surface of the Earth. Mining is required to obtain most materials that cannot be grown through agriculture, agricultural processes, or feasib ...

and

smelting Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron-making, iron, copper extraction, copper ...

operations and organic and inorganic fertilizer application.

Nanoparticles

Nanotechnology Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing propertie ...

is a rapidly growing industry with many applications, including

drug delivery Drug delivery involves various methods and technologies designed to transport pharmaceutical compounds to their target sites helping therapeutic effect. It involves principles related to drug preparation, route of administration, site-specif ...

biomedicine Biomedicine (also referred to as Western medicine, mainstream medicine or conventional medicine)

s, and electronics. As a result, manufactured nanoparticles, with sizes less than 100 nm, are released into the environment. Plant uptake and bioaccumulation of these nanoparticles can cause plant growth enhancement or phytotoxic effects, depending on plant species and nanoparticle concentration.

References

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