Biogeochemical Cycles - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 149

These compounds are diesters of phthalic acid. The annual world
production of phthalates exceeds more than 1 million metric tons. The phthalates
are mainly used as plasticizers, particularly to make polyvinylchloride (PVC) flex-
ible, and they are ubiquitous in the environment. In aqueous solution, like all
carboxylic acid esters, phthalates can hydrolyze to form the corresponding acid (i.e.,
phthalic acid) and alcohol(s) (i.e., ROH, R I OH).
Surfactants: Commercially available surfactants are not uniform substances but
mixtures of compounds of different carbon chain lengths. They have an amphiphilic
(partly hydrophilic and partly hydrophobic) characteristic and special properties that
render them unique among environmental chemicals. In aqueous solutions, they
distribute in such a manner that their concentration at the interfaces of water with
gas or solids is higher than it is in the inner regions of the solution. This results in
a change of system properties, e.g., a lowering of the interfacial tension between
water and an adjacent nonaqueous phase, and in a change of wetting properties.
Surfactants are also widely used as wetting agents, dispersing agents, and emulsifiers
in all kinds of consumer products and industrial applications. 107 Because of direct
use in water, a large portion of over 3 million metric tons of surfactants is annually
discharged into domestic and industrial wastewater. Since these compounds often
constitute a significant part of the organic carbon loading of wastewater, their
biological degradation is of particular interest. Giger et al. 108 found that during
biological treatment, toxic products were formed from nonionic surfactants of the
alkylphenol polyethyleneglycol ether type. Some of the toxic products were detected
in very high concentrations in sewage sludge. Examples of commercially important
surfactants include anionic surfactants (soaps, linear alkylbenzene sulfonates, sec-
ondary alkyl sulfonates, fatty alcohol sulfates), cationic surfactants (quaternary
ammonium chloride), and nonionic surfactants (alkylphenol polyethyleneglycol
ethers, fatty alcohol polyethyleneglycol ethers).
Pesticides (herbicides, insecticides, fungicides). In general, pesticides are syn-
thesized so as to have a specific detrimental biological effect on one or several target
organisms (e.g., plants, insects, and fungi), but (ideally) they should have little impact
on the rest of the living environment in which they are applied. In order to achieve
this goal, compounds with very special structures, often exhibiting several functional
groups, have to be employed. World pesticide consumption was estimated to be
around 5 million tons in 2000. 109 Because several functional groups are frequently
present in a pesticide molecule, the prediction of the distribution, mobility, and
reactivity of such compounds in the environment is often more difficult than that
for less complex chemicals. Pesticides, because they are toxic, are of utmost impor-
tance when they reach water resources by means of percolation or surface run-off.
Although certain characteristics of pesticides are well known, their exhibited char-
acteristics upon reaching a waterbody are extremely difficult to estimate. 110 WHO
and the U.S. EPA classify pesticides according to their toxicological effects. The
classifications are based on increasing acute LD 50 values in male mice (lethal dose
in 50% of the test animals). 111
The time lapse between pesticide application and the first rainfall event and the
rainfall intensity are the most important factors affecting the loss of pesticides from
agricultural land. A considerable part of total pesticide loss occurs during the first

Phthalates .