By: Bonnie L. Grant, Certified Urban Agriculturist
Phytotoxicity in plants can rise from a number of factors. What is phytotoxicity? It is anything chemical which causes an adverse reaction. As such, it can stem from pesticides, herbicides, fungicides and other chemical formulations. The plant’s response varies from discolored leaves all the way to death. The sensitivity can go both ways, however, since some plants are phototoxic to humans and can cause injury.
Phytotoxicity in plants usually occurs in those that are overly sensitive to chemicals. It can also occur when tank mixed chemicals are applied in hot weather or when an adjuvant or solvent is added to the tank mixture. Stressed plants are also more prone to sensitivity than those that are well watered and healthy.
Phytotoxicity can exist as a response to an external condition or as a defense to an external condition.
This dual effect is not found in all plants but some are more sensitive to chemicals than others. For instance, ferns, palms, English ivy, and poinsettias are all extremely sensitive to chemicals. Still other plants are sensitive to only certain chemicals.
Plants that are phytotoxic in the sense that they are sensitive to chemicals often have specific formulas to which they are vulnerable.
Stone fruits have a problem with copper, which is a component of Bordeaux mix, often applied to combat fungal diseases. It causes russeting in apples and can stunt the leaves. Copper also causes issues in cucurbit crops.
Zinc sulfate has the potential to defoliate fruit trees. Sulfur causes burns on roses, some ornamental plants and cucurbit crops.
Insecticides and herbicides that are mixed improperly, applied at the incorrect rate or have been mixed in a contaminated container can do a range of damage to many different plants.
Plants may release chemicals of their own as defense. These chemicals can harm humans. Usually, the phototoxicity symptoms will be topical.
Wild parsnip looks very much like its cultivated cousin but has phototoxicity which can cause burns. Contact with the plant and then subsequent exposure to the sun will cause a fiery sting in the contact area.
Mayapples have a similar defense mechanism and should not be touched. All parts of this plant are poisonous.
Even common garden plants can have mild phototoxicity and should be handled carefully. Wash your hands after handling or harvesting any of the following (wearing gloves is helpful too):
If you come in contact with a phototoxic plant, wash the area and apply a topical cream such as cortisone or a paste of baking soda and water.
Plants that experience phytotoxic symptoms should be rinsed off but usually the damage has already been done. To minimize the risk, always follow directions and apply chemicals on a cool, cloudy day. Use less toxic options like baking soda, phosphate salts, horticultural oils and soaps, and beneficial bacteria or insects.
Treatment for phytotoxicity in a small area of a plant may involve simply lopping off the stem to prevent the damage from interfering with the rest of the plant. Providing adequate water and good general care will usually rally the plant over time and reduce the chance of permanent injury.
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Poisonous plants are plants that produce toxins that deter herbivores from consuming them. Plants cannot move to escape their predators, so they must have other means of protecting themselves from herbivorous animals. Some plants have physical defenses such as thorns, spines and prickles, but by far the most common type of protection is chemical. 
Over millennia, through the process of natural selection, plants have evolved the means to produce a vast and complicated array of chemical compounds to deter herbivores. Tannin, for example, is a defensive compound that emerged relatively early in the evolutionary history of plants, while more complex molecules such as polyacetylenes are found in younger groups of plants such as the Asterales. Many of the known plant defense compounds primarily defend against consumption by insects, though other animals, including humans, that consume such plants may also experience negative effects, ranging from mild discomfort to death.
Many of these poisonous compounds also have important medicinal benefits.  The varieties of phytochemical defenses in plants are so numerous that many questions about them remain unanswered, including:
These questions and others constitute an active area of research in modern botany, with important implications for understanding plant evolution and medical science.
Below is an extensive, if incomplete, list of plants containing one or more poisonous parts that pose a serious risk of illness, injury, or death to humans or domestic animals. There is significant overlap between plants considered poisonous and those with psychotropic properties, some of which are toxic enough to present serious health risks at recreational doses. There is a distinction between plants that are poisonous because they naturally produce dangerous phytochemicals, and those that may become dangerous for other reasons, including but not limited to infection by bacterial, viral, or fungal parasites the uptake of toxic compounds through contaminated soil or groundwater and/or the ordinary processes of decay after the plant has died this list deals exclusively with plants that produce phytochemicals. Many plants, such as peanuts, produce compounds that are only dangerous to people who have developed an allergic reaction to them, and with a few exceptions, those plants are not included here (see list of allergens instead). Despite the wide variety of plants considered poisonous, human fatalities caused by poisonous plants – especially resulting from accidental ingestion – are rare in the developed world. 
Phytophotodermatitis happens when certain plant chemicals cause the skin to become inflamed following exposure to sunlight.
Phytophotodermatitis gets its name from the terms ‘phyto’ meaning plant, ‘photo’ meaning light, and ‘dermatitis’ meaning skin inflammation.
Also known as lime disease (which is not the same as Lyme disease), phytophotodermatitis symptoms include skin inflammation, itching, and blistering.
Share on Pinterest Phytophotodermatitis may be caused by exposure to both plant chemicals and sunlight together. Meadow grass is one plant that may cause this skin reaction.
The symptoms of phytophotodermatitis usually begin 24 hours after exposure and peak between 48-72 hours. Symptoms can be mild or severe and include:
The patches of blisters are usually irregularly shaped. The patterns represent the areas of the skin that were exposed to the chemical. For example, blisters in the pattern of drips may result from exposure to fruit juice. Streaks may indicate that a person brushed their skin against a plant.
When the initial symptoms subside, usually after 7-14 days , the skin may show signs of darkening, which is known as hyperpigmentation. This stage of phytophotodermatitis, known as post-inflammatory pigmentation, may last for many weeks or months.
Some people who experience only a very mild inflammatory reaction following sun exposure may not even be aware that they have had a reaction. The hyperpigmentation may be the first clue that they have developed phytophotodermatitis.
Wet skin, sweat, and heat can exacerbate the initial symptoms, while sun exposure can darken skin pigmentation.
Phytophotodermatitis occurs when someone is exposed to plant chemicals and subsequently exposed to sunlight.
Symptoms typically arise after direct contact with the plant, such as by touching.
Many plants and vegetables contain chemical compounds that cause sensitivity to sunlight. Such chemicals are known as photosensitizers. An example of a photosensitizer is psoralen.
Some common plants that contain psoralen include:
Also, it may be present in:
When exposed to UVA light, psoralen causes photochemical reactions in the skin. These responses damage skin cells and cause cell death, leading to the symptoms described above.
Anybody can be affected by phytophotodermatitis, regardless of gender, age, or race. However, several factors may increase the risk of experiencing phytophotodermatitis.
Activities that can trigger it include:
Certain professions can increase the risk, such as:
Doctors usually diagnose phytophotodermatitis by taking a person’s medical history and carrying out a physical examination. The doctor will ask about recent activities, exposure to plants, sun exposure, and current and previous symptoms. They will also examine the affected skin.
If the doctor is unsure or wishes to rule out other conditions, they may carry out further tests, such as a patch test or skin biopsy. Mild cases of phytophotodermatitis do not always necessitate medical care. However, if symptoms are severe or persist, a person should consult their doctor.
It should be noted that phytophotodermatitis is often misdiagnosed. It may be mistaken for :
Most cases of phytophotodermatitis clear up with minimal intervention. Treatment aims to reduce pain and shorten the duration of symptoms. Treatment options include:
Severe cases of phytophotodermatitis, or those involving more than 30 percent of the skin, may require hospital treatment that includes corticosteroid treatment and intravenous (IV) fluids.
Photochemotherapy is a type of UV treatment that is used for certain skin diseases, such as psoriasis. However, it is not recommended for phytophotodermatitis because it can make hyperpigmentation even darker.
Skin whitening should also be avoided in cases of phytophotodermatitis because this procedure has not been proven to help the condition.
In some cases, phytophotodermatitis can lead to the following complications:
The inflammatory skin reaction associated with phytophotodermatitis may be prevented by:
See a doctor if symptoms are:
Phytophotodermatitis is usually not serious and resolves quickly. Complications are uncommon. Recurrent cases of phytophotodermatitis suggest that the offending plant has not been identified.
Investigating herbicide drift cases should start when a grower observes unusual symptoms on their crops or observes nearby spraying during weather conditions that may cause drift. The following information should be collected to document herbicide drift incidents.
Here's a kicker – there are wide range of plants that can cause this condition that you might never suspect.
Plants that may cause phytophotodermatitis include (but are not limited to):
Those who are into botany will notice that the top six plants on the list are all related to each other (they are members of the Apiaceae family). Some of you may have also heard about getting blisters from wild parsnip or poison parsnip, but may not have realized the garden parsnips can also cause burns. Garden parsnip and wild parsnip are both different varieties of the same species – Pastinaca sativa. The veggies typically cause burns on agricultural workers and grocers, who handle large quantities of plant material.
The Medscape site shows a rather nasty blister that covers about 1/3 of the forearm of a flight attendant who spilled lime juice on her skin. The phytophotodermatitis from limes is also referred to as “margarita dermatitis” because of all those poor folks who have sucked on their limes in the summer sun.
The wild parsnip burns (and those from other wild plants like hogweed or queen Anne's lace) can be some of the worst, because people do terrible things like running weed whackers with shorts on and get their legs all covered with little bits of parsnip (and sap), like the poor guy featured in the article “Burned by Wild Parsnip” in Wisconsin Natural Resources magazine. The photo below is as example of how large the blisters can get.
Wood nettle is an herbaceous plant typically found in moist areas of woodlands. It tends to grow in large, dense patches, which can provide cover for wildlife. It is also a host plant for a number of insects and butterflies. It stands about 2 to 4 feet tall and has light- to medium-green stems covered with stiff, white hairs that sting when they’re rubbed against.
The leaves of the wood nettle plant are medium- to dark green, roughly oval-shaped, and serrated. Young leaves are densely covered with stinging hairs, while older leaves tend to have fewer of them, often located on the underside of the leaf. In summer the wood nettle blooms, with lacy strands of white flowers.
The sting from wood nettle usually subsides within an hour. You may also be able to reduce the irritation by pouring water over the irritated area when you notice the stinging, then washing the area with soap and water.
Some people collect wood nettle for food and sauté or steam it like a green vegetable.
The transition elements platinum, palladium, and rhodium are
widely used in the automobile industry. Production of catalytic
converters is the principal application field of the so called
Platinum Group Elements (PGE). Since the introduction of
autocatalysts to reduce the emission of the greenhouse gases
CO, NOX, and HC, the concentration of PGE in environmental
samples such as road dusts, soils, and plants is steadily
increasing. The uptake pathways, accumulation, and transport of
PGE emitted from autocatalysts in crop plants are poorly
understood. However, the present study deals with these subjects
in addition to the phytotoxicity of these metals on crop plants.
Field experiments with lettuce (Lactuca sativa L.) were
conducted at two sites. The first site lies close to the German
Highway A5 and the second site is within the botanical garden of
the University of Karlsruhe/Germany. The expected emissions of
PGE at the highway site were higher than those at the botanical
garden site. In addition to an expected atmospheric uptake by
aerial organs, PGE uptake via plant roots was enabled by
separate addition of two catalysts powders containing the three
. mehr noble metals, platinum, palladium and rhodium. Furthermore,
greenhouse experiments using PGE soluble chloride salts that
were added to the hydroponic medium, were conducted with potato
(Solanum tuberosum L.), barley (Hordeum Vulgare L.), and lettuce
(Lactuca sativa L.) under controlled conditions, whereby the
uptake was exclusively made via the plant roots. The crop
plants were divided into their organs and the PGE concentrations
were determined using HRICP-MS. The phytotoxicity of PGE on the
crop plants was visibly manifested and some physiological
parameters were determined. Lettuce (Lactuca sativa L.) plants
that were treated with the catalysts powders showed higher PGE
concentrations than the control ones, implying the uptake of the
precious metals via the plant roots. PGE concentrations
determined in the field grown lettuce (Lactuca sativa L.)
demonstrate, not only the solubility of platinum, palladium, and
rhodium in the soil, but also the higher bioavailability of
palladium, rather than platinum and rhodium. Platinum and
palladium are mainly retained in the roots of the crop plants
grown in the growth chamber. The noble metals are translocated
from roots to shoots showing high mobility within the plants and
phototoxic symptoms were more severe in potatoes (Solanum
tuberosum L.) than in lettuce (Lactuca sativa L.) and barley
(Hordeum Vulgare L.). Palladium, to a higher extent than
platinum, is mainly retained in plant roots, whilst platinum to
a higher extent, is taken up into aerial organs. The
Monocotyledonous (barley) plant showed an overall higher total
concentration, but lower shoot platinum and palladium
concentrations than the dicotyledonous one (potato). Potato
(Solanum tuberosum L.) accumulated more platinum and palladium
than lettuce (Lactuca sativa L.). Palladium is not only more
mobile within the potato and lettuce than platinum, but was also
severely toxic on the potato (Solanum tuberosum L.) when
compared to platinum. There were no severe phytotoxic effects
from the PGE on barley (Hordeum Vulgare L.) and lettuce (Lactuca
sativa L.). Visible phytotoxic symptoms observed in the crop
plants are stunted growth, chlorosis, blackening of the root
system, small leaves, and brown patches on leaves. It has
clearly been established that the differences in platinum and
palladium concentrations in potato (Solanum tuberosum L.) organs
were due to the differences in phytotoxic effects of both
elements on plants rather differences in amount of platinum or
palladium applied for the uptake. The principal difference
between platinum and palladium was seen in the portion taken up
into either the aerial parts or retained in the roots of the
three plant species.
Die Übergangsmetalle, Platin, Palladium und Rhodium werden
weltweit in der Automobilindustrie verwendet. Die Herstellung
der Autoabgaskatalysatoren zählt zu den Hauptanwendungen der
sogenannten Platingruppenelemente (PGE). Seit der Einführung der
Autoabgaskatalysatoren, um die Emissionen der Treibhausgase CO,
NOx und HC zu reduzieren, nimmt die Konzentration der PGE in den
Umweltproben wie Strassensedimenten, Böden und Pflanzen ständig
zu. Die Aufnahmepfade, Akkumulation und der Transport der
aus den Abgaskataysatoren emittierten PGE in den Nutzpflanzen
sind wenig bekannt. Die vorliegende Arbeit befasst sich
zusätzlich zu der Phytotoxizität dieser Metalle auf
Nutzpflanzen mit diesen Themen. Es wurden an zwei Standorten
Feldversuche mit Salat (Lactuca sativa L.) durchgeführt. Der
erste Standort liegt direkt an der A5 und der zweite
innerhalb des Botanischen Gartens der Universität Karlsruhe. Die
erwarteten Emissionen der PGE an dem Autobahn-Standort waren
höher als die am Standort Botanischen Garten.
Zusätzlich zu einer atmosphärischen Aufnahme über die
oberirdischen Pflanzenorganen wurde die Aufnahme über die
Pflanzenwurzel ermöglicht. Dies geschah durch getrennten
Zusatz von zwei Katalysatorenpulver, die die Edelmetalle Platin,
Palladium und Rhodium in unterschiedlichen Konzentrationen
Überdies wurden Gewächshausversuche mit Kartoffeln (Solanum
tuberosum L.), Gerste (Hordeum Vulgare L.) und Salat (Lactuca
sativa L.) unter kontrollierten Bedingungen durchgeführt, um die
Aufnahme ausschließlich über die Wurzel zu ermöglichen. Als
Kontaminationsquelle wurden lösliche PGE-Chloridsalze verwendet.
Die Nutzpflanzen wurden in einzelne Pflanzenorgane unterteilt
und deren Gehalte an PGE mittels HR-ICP-MS bestimmt. Die
phytotoxischen Auswirkungen der PGE auf die Nutzpflanzen wurden
visuell manifestiert und die pflanzenphysiologischen Parameter
ermittelt. Die Salatpflanzen, die mit Katalysatorpulver
behandelt waren, zeigten einen höheren PGE-Gehalt als die
Kontrollpflanzen, was die Aufnahme der Edelmetalle über die
Die ermittelten PGE Konzentrationen im feldgewachsenen Salat
(Lactuca sativa L.) sehen nicht nur die Löslichkeit von Platin,
Palladium und Rhodium im Boden vorraus, sondern auch die höhere
Bioverfügbarkeit von Palladium eher als die von Platin und
Rhodium. Platin und Palladium wurden hauptsächlich in den
Wurzeln der Nutzpflanzen, die im Gewächshaus angepflanzt waren,
retentiert. Die Edelmetalle wurden von der Wurzel in den Spross
transportiert, was die hohe Mobilität innerhalb der Pflanzen
zeigt. Die phytotoxischen Symptome waren schwerwiegender bei den
Kartoffeln (Solanum tuberosum L.) als bei der Geste (Hordeum
Vulgare L.) und dem Salat (Lactuca sativa L.), die im
Gewächshaus angezogen waren. Palladium wurde, in größerem Umfang
als Platin, hauptsächlichen in den Wurzeln der
Gewächshauspflanzen retentiert während Platium in größerem
Umfang als Palladium in den Spross aufgenommen wurde. Die
monocotyle Pflanze (Gerste) zeigte insgesamt höhere
Konzentrationen, aber niedrigere Platin- und
Palladiumkonzentrationen im Spross als die dicotyle Pflanze
(Kartoffel). Die Kartoffel (Solanum tuberosum L.) akkumulierte
mehr Platin und Palladium als Salat (Lactuca sativa L.). Das
Palladium war innerhalb von Kartoffel und Salat nicht nur
mobiler als Platin, sondern hatte im Vergleich zu Platin auch
sehr toxische Auswirkungen auf die Kartoffelpflanzen, die im
Gewächshaus angezogen waren. Hingegen waren keine schweren
toxischen Auswirkungen der PGE auf Gerste (Hordeum Vulgare L.)
und Salat (Lactuca sativa L.) zu beobachten. Die sichtbaren
phytotoxischen Symptome, die bei den Gewächshauspflanzen
beobachtet wurden, waren verkümmertes Wachstum, Chlorosis,
Schwärzung des Wurzelwerkes, kleine Blätter sowie braune Flecken
auf den Blättern. Es wurde deutlich gezeigt, dass die
Unterschiede im Platin und Palladiumgehalt in den
Kartoffelorganen auf die unterschiedlichen phytotoxischen
Auswirkungen der beiden Metalle auf die Pflanzen zurückzuführen
sind. Diese Unterschiede waren unabhängig von den Mengen an
Platin und Palladium, die für die Aufnahme eingesetzt waren. Der
Hauptunterschied zwischen Platin und Palladium waren die Mengen,
die entweder in den oberirdischen Organen aufgenommen oder in
den Wurzeln der drei Pflanzen retentiert wurde.