Noise is one of the common environmental pollutants that can cause damage to various systems of the body, including specific auditory system damage and non-specific auditory damage. The degree of noise damage is usually related to the intensity of the noise, the duration of noise exposure and the mode of exposure. Although low-intensity noise does not generally cause health effects, high-intensity noise can cause headaches, dizziness, memory loss, developmental physical abnormalities, emotional and behavioral abnormalities, sleep disturbances, hearing loss, and other problems.
1.Noise
1.1 Definition of noise
In terms of physical properties, noise is the sound emitted when the occurring body does irregular vibration. Such as the sound of the engine and horn of the traffic vehicles on the street; the sound of various machines and equipment in large mechanized factories and construction sites; the sound of firecrackers, footsteps, etc. In terms of human physiology and psychology, any sound that prevents people from resting, studying and working normally, as well as the sound that interferes with the sound people want to listen to, in this sense, there are many sources of noise, the sound of cars on the street, the sound of talking in a quiet library, the sound of machines on construction sites, and the sound of neighbors’ TV sets that are too loud, are all noise. Noise is a sound that we do not need. Noise is expressed in several physical parameters such as intensity, frequency, period, and duration, and its intensity is expressed in decibels (dB).
1.2 Classification of noise.
0 – 2 0 db is very quiet, almost imperceptible; 2 0 – 4 0 db is quiet, like a whisper; 4 0 – 6 0 db is general, ordinary indoor conversation; 6 0 – 7 0 db is noisy, nerve damage; 7 0 – 9 0 db is very noisy, nerve cells are damaged; 9 0 – 1 0 0 db noise increased, hearing damage; 1 0 0 – 1 2 0 db is unbearable, stay a minute that is temporarily deaf; In 2009, the World Health Organization (WHO) statistics on the impact of the decibel level of external sound on the human body at night are as follows: less than 30 db will have no clear impact on the human body; 30-40 db will have an impact on a part of the sensitive population in the initial stage of sleep; 40-55 db will have an increase in the number of people affected, and the sensitive People will have a serious impact; greater than 55db is easy to produce adverse effects on people, and a high percentage of people will be angry as a result.
2. Environmental noise affects growth and development and behavior
2.1 Noise affects growth and development
The impact of noise in growth and development is mainly damage to the auditory system. A study by foreign scholars showed that 1/2 of the children of female textile workers who worked in a noisy environment with sound intensity of 100 db and above during pregnancy had hearing loss in the high frequency band of 20-55 db [4]. Another study investigated 131 mothers whose mothers were exposed to noise intensities of 85-95 db during pregnancy and showed that 24.1% of these children had a hearing loss of 10 db or more in the high frequency band (at 4000 Hz). These studies suggest that noise has a direct effect on the auditory system during fetal development. The cochlea of the fetal inner ear begins to grow and develop from the 20th week of gestation and continues to do so until the baby is more than 30 days old. Because the cochlea of the fetal inner ear is in its growth and developmental phase, it is highly susceptible to damage from high-intensity noise.
Some scholars have studied the effects of airport noise on fetal development. A study by Japanese scholars showed that the birth rate of premature babies increased in the area around Osaka Airport, and the weight of full-term newborns in the noise-polluted area was mostly below 2,000g (normal full-term newborns weigh more than 2,500g), which is equivalent to the weight of premature babies, indicating that the strong noise probably affected the normal physical development of the fetus.
American scholars have studied more than 10,000 infants and confirmed that the malformation rate of infants born near airports increased from 0.8% to 1.2% compared with the normal environment, mainly including spinal malformation, abdominal malformation and brain malformation, indicating that strong noise may directly affect the expression and regulation of fetal genes, causing mutations that cause malformations. It has also been found that infants born in noisy environments have weaker body resistance, and the average number of illnesses per year before the age of 3 is 2 to 4 times more than those born in ordinary environments.
Not much research has been done on the effects of noise on animal growth and development. Noise disturbance can cause a decrease in appetite and abnormal stool traits, indicating that noise, as a harmful physical stimulus, affects the growth and development of mice, and the functions of their digestive system and nervous system, etc., have been affected. In addition, noise can cause a decrease in saliva and gastric juice secretion, decrease in acidity of digestive juice, decrease in frequency and amplitude of gastrointestinal peristalsis, and slow down the digestive process, thus affecting the growth and development of animals.
2.2 Noise affects learning memory and mechanism
Research on noise has focused on its effects and mechanisms on the nervous system, especially on learning and memory interference. Learning and memory are one of the most characteristic physiological features of higher animals and humans, and it belongs to higher neural activities or higher functions of the brain. Psychological studies have concluded that learning is the process by which a person acquires new patterns of behavior or experience, mainly through the nervous system in combination with changes in the external environment. Memory, on the other hand, is the process of storing and reinforcing the acquired behavior or experience under essentially unchanged environmental conditions. Learning and memory are always closely linked, and the learning process requires memory, otherwise it would not be able to influence people’s behavior through learning. Recent studies have shown that noise exposure can inhibit learning and memory functions in humans and animals, and the process is related to a variety of neurotransmitters.
For example, increased excitability of norepinephrine (NE) neurons can improve learning memory, and its decreased excitability can diminish learning memory function. 5-hydroxytryptamine (5-HT) has a predominantly excitatory role in the learning memory process and can trigger the ease of learning memory ability. Dopamine (DA) indirectly affects memory capacity by regulating mental activity, emotion, recognition, thinking and reasoning processes.
Domestic scholars have tested the children of female workers who were frequently exposed to strong noise (95 db) during pregnancy and compared them with other children in similar conditions, and found that the IQ of children born to pregnant women who were frequently exposed to noise environment was lower than that of the latter, and some of the fetuses had abnormal personality development and were withdrawn and irritable after birth. It is assumed that the reason for this is that the long-term exposure of pregnant women to strong noise may cause uterine contraction, which affects the blood supply of the fetus and thus the development of the fetal nervous system.
Some studies have shown that long-term aircraft noise exposure was associated with impaired reading ability, decreased long-term memory capacity and the emergence of boredom in children through a survey of children near airports; Lercher et al. found through a survey of a large number of elementary school students aged 8-11 years that environmental noise generated by railroads, roads and highways could cause a decrease in children’s mental health index as well as poor classroom performance, and This correlation was more pronounced in preterm and low birth weight infants. Tsaneva’s study showed that the effect of masking noise on the organism was mainly on memory-related psychophysiological task performance.
Recently, it has been suggested that the effect of noise on neurological learning memory may be related to oxytocin. Studies have shown that noise can increase plasma levels of oxytocin in women. Oxytocin is secreted by neurosecretory cells in the paraventricular nucleus and the external region of the median eminence into the pituitary portal circulation, and has been shown to impair neurological integration and reproduction of memory.
Ravindran et al. found that exposure to white noise affected the levels of central neurotransmitters, including NE, epinephrine, DA, and 5-HT, in the brain of rats. Mcdonald et al. found that 5-HT2A receptors are involved in the regulation of chronic stress effects and that the use of 5-HT2A receptor antagonists can antagonize the adverse effects of noise on cognitive function. Prior suggested that noise affects learning ability by first affecting memory formation and remodeling.
In addition to neurotransmitters, the effects of noise on learning and memory are closely related to neuronal electrical activity. One study reported that repeated exposure to 105 dB white noise had a significant inhibitory effect on the electrical activity of neurons in the cA3 region of the rat hippocampus and could cause detrimental changes in synaptic ultrastructure such as the lack of concentration of vesicles in the presynaptic membrane and increased vacuolization of mitochondria; Ouyang Wei et al. showed that noise could reduce the activity of hippocampal denervation neurons, decrease the synthesis of nitric oxide synthase (Nos), affect The study by Ouyang Wei et al. showed that noise could reduce hippocampal denervation activity, decrease nitric oxide synthase (Nos) synthesis, affect memory acquisition and retention, and delay the conversion of short-term to long-term memory. In addition, noise also blocked the acquired long-term enhancement of synaptic effects in the CA3 region of the hippocampus in rats.
Comprehensive related studies suggest that noise interference leads to decreased learning ability by the following two possible mechanisms: first, temporary brain ischemia and hypoxic changes caused by noise exposure inhibit the normal activity of nerve cells in animals, thus possibly blocking the conversion process of short-term memory to long-term memory, and therefore manifesting as diminished learning ability. Secondly, some scholars found that noise affects learning memory related to the hippocampus in the brain part of animals, which is known to have an important role in learning memory, while noise mainly inhibits the electrical activity of neurons in the CA3 area of the hippocampus.
3.Strategies for coping with adverse noise environment
Individual protection against noise is traditionally based on protection against auditory system damage. Among them, wearing ear protectors is an economical and effective measure for individual noise protection. According to their working principle, ear protectors can be divided into two categories: active and passive; according to their structure, they can be divided into four categories: ear plugs, earmuffs, helmets and communication headsets, among which ear plugs are most commonly used and convenient. Preventive treatment measures after entering a noisy environment mainly include the following modalities.
(1) Improving microcirculation with drugs such as carbogen, corticosteroids, adenosine triphosphate, sodium nitroprusside (SNP), low molecular dextran, ginkgo biloba preparations, chuanxiong, salvia and geranoside;
(2) Drugs that promote neurotrophic metabolism, including neurotrophic factor, vitamin B1, vitamin B12, etc;
(3) Oxygen radical scavenging drugs, including antioxidants SOD, vitamin C, vitamin E, R-PIA, etc;
(4) others, such as nitric oxide synthase inhibitors, Glu receptor antagonists (D-AP-5, MK-801) and lipid peroxidation inhibitors U74389F.
Some recent studies have shown that taking certain measures can reduce the adverse effects of noise on the learning memory function of the nervous system. Gu Zhengyu et al. found that short- and long-term memory was not significantly impaired in mice exposed to both 93 dB steady-state white noise and inhalation of (8-10)x106/cm3 negative air ions, while both short- and long-term memory was significantly impaired in mice that did not inhale negative air ions. This suggests that negative air ions have a protective effect on the reduction of learning memory function of the nervous system induced by noise effects.
In addition, tranquilizers can block the reticulo-upper agonist system pathway, thus avoiding the CNS effects caused by noise acting on a wide area of the cerebral cortex, so that noise can only pass through the specific projection system. The results of Liu Yanghong et al. also suggest that calcium antagonists have a protective effect against psychological stress induced by noise stimulation. In addition, Wang Bin [31] et al. used anti-free radical drugs to prevent the decrease in learning memory capacity caused by infrasound effects, which proved to be effective, but further studies are needed.
In summary: The effects of noise on neuropsychological and growth and development have been of great concern, especially the effects of noise on learning and memory functions, causing a decrease in work and learning efficiency, health and quality of life in exposed populations. However, the specific neurophysiological mechanisms of this effect are not well understood, and its effects on children’s growth and development in particular need further study in order to establish a comprehensive set of protective measures that can improve the overall health and ergonomics of the population.