In the previous part of this book review, we presented the CABI publication A Handbook of Environmental Toxicology: Human Disorders and Ecotoxicology edited by Felix J. P. D’Mello. Among selected topics from the compilation in the handbook, we listed examples of environmental pollutants of toxicological significance arranged by their origin. The previous part discussed compounds of natural and agricultural origin. That list continues in this part with other groups of toxic substances we consider particularly relevant from the aspect of environmental health.

Compounds of industrial origin

Polychlorinated biphenyls (PCB)

Polychlorinated biphenyls are listed as very common pollutants. They are chemical partially or fully chlorine-substituted derivatives of biphenyl (two benzene moieties connected by a single covalent bond between carbon atoms in each aromatic ring). PCBs have been detected in animal fat, butter, as well as fish (e.g., fish liver, fish oil). PCBs accumulate in humans in the adipose tissue and fat-rich organs (e.g., breast, testicles, ovaries, brain). In breast milk, especially PCB congeners containing several chlorine atoms accumulate in substantial concentrations. Most of their congeners are mutagenic, carcinogenic and reprotoxic and their hormone-modulating effects are also known. Their regulation strictened in the late 1970s due to concerns about their environmental persistence and human health risks. Despite the tightening, the environmental level of PCBs has not declined significantly over the past two decades, and more recently, in industrial mixtures, today’s PCBs have been identified as by-products of modern pigment production processes. Developmental neurotoxicity symptoms attributed to PCBs include disruption of thyroid hormone signaling, altered neurotransmitter signaling, calcium homeostasis disorder, and induction of oxidative stress. Of these, the calcium problem is the most sensitive. Experimental data suggested a causal relationship between the effect of PCB on calcium signals and the disruption of critical neurodevelopmental processes, especially dendritic arborization and apoptosis.

Microplastics

The apparently vast emergence of disintegrated debris of plastic materials is certainly the latest environmental problem of our time. We have not foreseen and certainly not considered the ability of most man-made plastic materials to decompose and fragment to micro- and nanodispersion levels. The amount of this novel type of environmental pollutant is enormous, and its effects are significant not only in marine but also in freshwater environments. Among these contaminants, nanoplastics can reach physiological sites where their effects triggered are still not completely elucidated. In addition to the problem with the plastic content, leaching of the plasticizers used during manufacturing also results in separate physiological effects, which in the case of older types of plastics is identified in the field of endocrine disruption. Perhaps the most shocking one of this type of pollutants is the case of plastic-bottled mineral waters and soft drinks, in which microplastic content is an order of magnitude higher than that in tap water. Food packaging without the use of plastics is one of the most serious and unresolved issues in the food industry today.

Compounds of industrial and agricultural origin

Nitrogen dioxide

Nitrogen oxides are emitted into the atmosphere from numerous sources. Nitrogen dioxide (NO₂) is produced in large quantities, for example, during manufacturing nitrogen fertilizers. It is also ubiquitous in motor vehicle exhaust gases and as such, it is one of the causes of the acid rain. The so-called silo filler’s disease is caused by NO₂ released during fermentation processes during the preparation of corn silage. Thus, this type of environmental pollution is directly related to agriculture. NO₂ causes acute lung damage and possibly death when inhaled. Acute exposure to a lower concentration of NO₂ (0.5-15 ppm) may increase respiratory sensitivity, especially in patients with obstructive pulmonary diseases. The effects of chronic exposure to environmental NO₂ (<0.5 ppm) are much more difficult to quantify, partly due to low concentrations and the existence of other co-pollutants. Since NO₂ is a reactive gas, it is still possible that prolonged exposure to the ambient concentration of NO₂ can result in cellular and biochemical changes that ultimately cause lung dysfunction.

Polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons or PAHs contain condensed aromatic rings and therefore are quite lipophilic substances. Their best-known representative is perhaps benzo-a-pyrene (BaP) that IARC has found to be carcinogenic in humans (category ‘1’). It has been linked to skin and lung cancer. It was found to be a testosterone antagonist in rat males, reducing testicular weight and testosterone production. PAH compounds cause significant exposure in several professions (coal gas extraction, coking, coal tar distillation, chimney sweeping – see chimney sweeps’ carcinoma – asphalt plating, aluminum production, etc.), where occupational harm is highly likely to lead to malignant lung disease. Many are emitted by the transport sector, especially by diesel vehicles. PAH compounds other than BaP are likely or possible carcinogens. Mixtures of PAH compounds can be found in smoked or overcooked dishes, margarines, roasted coffee, cooking oil used several times. Their frequently mentioned representatives: phenanthrene, anthracene, naphthalene, BaP, and due to their severe health concerns, several of them have been specified as priority pollutants (e.g., the list of the 16 priority PAHs specified by the US Environmental Protection Agency or priority pollutants specified in the EU Water Framework Directive). Their presence is observable everywhere: in water, air, and soil. PAHs have adverse effects on aquatic organisms at all stages of life, and these effects include growth reduction, DNA damage, cytotoxicity, hormone modulation, and immunosuppression.

Endocrine disruptors (EDCs)

Quite a number among pesticide active ingredients have been found to exert hormone modulating activity. Awareness and withdrawal of given pesticides due to their effects on the endocrine system started in the nineties, and the European Food Safety Authority (EFSA) commenced its review program on possible endocrine disruption of regulated products over a decade ago. Exposure to estrogen agonist compounds (e.g., atrazine) can lead to reverse mating and egg-laying neo-female from a ZZ male of frogs, while testosterone agonists can also be used to produce a reverse neo-male from a Zw female of fish (see AquAdvantage salmon). Among common environmental pollutants, main suspects for worsening our male (low sperm count) and female fertility (endometriosis) statistics, as well as causing hormone-dependent tumors (testicular, prostate, breast, endometrial and thyroid cancers) are pesticide residues (especially chlorinated hydrocarbons) and plastic softeners (e.g., phthalates used for plasticizing PVC, PET, HDPE, and other plastics). The hormone-modulating effect of bisphenol has been known for almost 80 years, but its market is steadily upwards: in 2016, its annual turnover was about 8 million tons. Among fungicides azole compounds (along with related derivatives used as pharmaceuticals); among herbicides triazine and sulfuron type compounds and glyphosate; while among insecticides chlorinated hydrocarbons, chlorpyrifos and pyrethroids are those that particularly fall in the range of the EDC reassessment program of the European Union. As of today, EDC chemicals include pesticides, industrial chemicals such as PCBs, combustion products (polychlorinated dibenzodioxins and -furans), plasticizers (bisphenol A, phthalates), surfactants (alkylphenols), flame retardants (polybrominated diphenyl ethers), various coatings (perfluorinated compounds) and a number of antimicrobials (parabens, triclosan) in personal care products, ingredients used in antiperspirants (aluminum salts), conditioning (cyclic volatile methylsiloxanes), UV filters (benzophenones) and fragrances (butylphenylmethylproprianol, polycyclic and nitro musks).

Heavy metals

According to the analysis of the monitoring results in the EU Rapid Alert System for Food and Feed (RASFF), the most common hazardous contamination of marine predatory fish (swordfish, tuna, and sharks) is mercury (causing e.g., Minamata disease). Fish shipments from Thailand, Vietnam and Spain are often rejected due to heavy metal contamination. In 2000, the Romanian mining company Aurul contaminated river Tisza with several heavy metals but mainly mercury, decimating its wildlife and polluting its sediments. A review of the meat of fish that feed on sedimentary animals would be timely in our days. Currently, the pollution of river Sajó in Slovakia is the concern of domestic environmental protection, which is the responsibility of the Siderit mining company (Nižná Slaná, Gabriela shaft).

In our country, lead pipes were used in connection with plumbing, and in rechargeable lead-acid batteries of the old type. In the premises of former battery dismantling factories lead contamination on the soil may be significant due to dusting lead particles. A substantial amount of lead has also entered the environment in the oil sludge of the Cséry plant. Food contamination by heavy metals is also considerable: in the RASFF database 10% of the detected contamination cases corresponded to heavy metals. Alerts regarding carrots of Turkish and Polish origin have also been issued (carrots tend to accumulate and store heavy metals).

Phosphate fertilizers from Eastern export became known in Hungary to have high levels of cadmium contamination, and thus, consumers may suffer exposures from crops and produce. Cadmium exposure risk via marine fish (e.g., tuna), squid, octopus and shellfish can also be measureable. The IARC classified several cadmiums salts as category ‘1’, certainly human carcinogens. Since the 1970s, the effect of cadmium intake on systolic blood pressure and atrioventricular conduction of the heart has been observed in rats, and growing evidence emerged that cadmium exposure may be associated with cardiovascular diseases.

Summary

Felix D’Mello’s handbook is an excellent summary of contemporary knowledge of environmental toxicology. It contains 40 chapters on diverging topics, some written by Felix D’Mello himself or by esteemed experts of the field. It covers environmental problems ranging from abiotic stress and natural or man-made toxins to airborne particulate matter, soil contamination and remediation, or nuclear radiation. It strongly attempts to establish and report causal relationships, if exist, among contamination cases and human and environmental health conditions, and claim unequivocal evidence associating environmental contaminants with human morbidity and ecological degradation. Nonetheless, it contains certain shortcomings, debatable statements and even chapters that have been discussed in this book review. A particular shortcoming is that there are embarrassingly few illustrations and images in the book, while the topic would make or even require the placement of many visual demonstrations possible. Altogether, however, it is a highly recommended textbook for those interested in current causes of human and environmental health problems.

The authors: Béla Darvas PhD, DSc of the Hungarian Academy of Sciences (biology), founding president of the Hungarian Society of Ecotoxicology, e-mail: [email protected]; András Székács PhD, DSc of the Hungarian Academy of Sciences (chemistry), one of the board members of the Hungarian Society of Ecotoxicology, e-mail: [email protected].

The text is the reviewer's non-edited original English version.