Pesticide leaching
Pesticide leaching occurs when pesticides mix with water and move through the soil,
ultimately contaminating groundwater. The amount of leaching is correlated with
particular soil and pesticide characteristics and the degree of rainfall and irrigation.
Leaching is most likely to happen if using a water-soluble pesticide, when the soil tends
to be sandy in texture, if excessive watering occurs just after pesticide application, if
the adsorption ability of the pesticide to the soil is low. Leaching may not only originate
from treated fields, but also from pesticide mixing areas, pesticide application
machinery washing sites, or disposal areas.
Fertilizers
Only a fraction of the nitrogen-based fertilizers is converted to produce and other plant
matter. The remainder accumulates in the soil or lost as runoff. High application rates
of nitrogen-containing fertilizers combined with the high water-solubility of nitrate leads
to increased runof] into surface water as well as leaching into groundwater, thereby
causing groundwater pollution. The excessive use of nitrogen-containing fertilizers (be
they synthetic or natural) is particularly damaging, as much of the nitrogen that is not
taken up by plants is transformed into nitrate which is easily leached. Nitrate levels
above 10 mg/L (10 ppm) in groundwater can cause "blue baby syndrome" (acquired
methemoglobinemia). The nutrients, especially nitrates, in fertilizers can cause
problems for natural habitats and for human health if they are washed off soil into
watercourses or leached through soil into groundwater.
Cadmium
The concentration of cadmium in phosphorus-containing fertilizers varies considerably
and can be problematic Continuous use of high-cadmium fertilizer can contaminate soil
and plants. Limits to the cadmium content of phosphate fertilizers has been considered
by the European Commission. Producers of phosphorus-containing fertilizers now select
phosphate rock based on the cadmium content.
Fluoride
Phosphate rocks contain high levels of fluoride. Consequently, the widespread use of
phosphate fertilizers has increased soil fluoride concentrations. It has been found that
food contamination from fertilizer is of little concern as plants accumulate little fluoride
from the soil; of greater concern is the possibility of fluoride toxicity to livestock that
ingest contaminated soils. Also of possible concern are the effects of fluoride on soil
microorganisms.
Radioactive elements
The radioactive content of the fertilizers varies considerably and depends both on their
concentrations in the parent min. Where high annual rates of phosphorus fertilizer are
used, this can result in uranium-238 concentrations in soils and drainage waters that
are several times greater than are normally present eral and on the fertilizer production
process
Other metals
Steel industry wastes, which are recycled into fertilizers for their high levels of zinc can
include the following toxic metals: lead, arsenic, cadmium, chromium, and nickel. The
most common toxic elements in this type of fertilizer are mercury, lead, and arsenic.
These potentially harmful impurities can be removed; however, this significantly
increases cost. Highly pure fertilizers are widely available and perhaps best known as
the highly water-soluble fertilizers containing blue dyes used around households, such
as Miracle-Gro. These highly water-soluble fertilizers are used in the plant nursery
business and are available in larger packages at significantly less cost than retail
quantities. There are also some inexpensive retail granular garden fertilizers made with
high purity ingredients.
Organic contaminants
Manures and biosolids contain many nutrients consumed by animals and humans in the
form of food. The practice of returning such waste products to agricultural land
presents an opportunity to recycle soil nutrients. The challenge is that manures and
biosolids contain not only nutrients such as carbon, nitrogen, and phosphorus, but they
may also contain contaminants, including pharmaceuticals and personal care products
(PPCPs). There is a wide variety and vast quantity of PPCPs consumed by both humans
and animals, and each has unique chemistry in terrestrial and aquatic environments. As
such, not all have been assessed for their effects on soil, water, and air quality. The US
Environmental Protection Agency (EPA) has surveyed sewage sludge from wastewater
treatment plants across the US to assess levels of various PPCPs present.
Heavy metals
The major inputs of heavy metals (e.g. lead, cadmium, arsenic, mercury) into
agricultural systems are fertilizers, organic wastes such as manures, and industrial
byproduct wastes. Some farming techniques, such as irrigation, can lead to
accumulation of selenium (Se) that occurs naturally in the soil. This can result in
downstream water reservoirs containing concentrations of selenium that are toxic to
wildlife, livestock, and humans. This process is known as the “Kesterson Effect,”
eponymously named after a reservoir in the San Joaquin Valley (California, USA), which
was declared a toxic waste dump in 1987 (see: Kesterson Reservoir).
Soil erosion and sedimentation
Agriculture contributes greatly to soil erosion and sediment deposition through intensive
management or inefficient land cover. It is estimated that agricultural land
degradation is leading to an irreversible decline in fertility on about 6 million ha of
fertile land each year. The accumulation of sediments (i.e. sedimentation) in runoff
water affects water quality in various ways. Sedimentation can decrease the transport
capacity of ditches, streams, rivers, and navigation channels. It can also limit the
amount of light penetrating the water, which affects aquatic biota. The resulting
turbidity from sedimentation can interfere with feeding habits of fishes, affecting
population dynamics. Sedimentation also affects the transport and accumulation of
pollutants, including phosphorus and various pesticides.
NatalieR answered the question on May 24, 2022 at 07:17